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H2O

49 CVEs product

Monthly

CVE-2026-54340 Jul 17, 00:16 HIGH This Week

Remote denial of service in the h2o HTTP server (all versions prior to commit 9265bdd) allows unauthenticated attackers to exhaust server memory by combining HPACK header-decompression amplification with Slowloris-style HTTP/2 stream stalling. By opening many streams that stall mid-request, an attacker forces the server to retain large volumes of amplified decoded header state, degrading or crashing the service. There is no public exploit identified at time of analysis, and the CVSS 7.5 (A:H only) reflects an availability-only impact with no confidentiality or integrity effect.

Denial Of Service H2O
NVD GitHub VulDB
CVSS 3.1
7.5
EPSS
0.3%
CVE-2026-44453 Jul 16, 23:16 HIGH This Week

Denial of service in the h2o HTTP server (all versions prior to commit 6b5370d) allows remote unauthenticated attackers to crash the server by requesting static files whose on-stack path construction via alloca can reach ~600KB, exceeding musl libc's default 128KB pthread stack and triggering a guard-page segmentation fault. The flaw is a CWE-770 uncontrolled resource allocation issue affecting availability only (CVSS 7.5, A:H). There is no public exploit identified at time of analysis and it is not listed in CISA KEV, but exploitation is trivial where h2o is built against musl libc.

Denial Of Service H2O
NVD GitHub VulDB
CVSS 3.1
7.5
EPSS
0.3%
CVE-2026-44436 Jul 16, 22:44 HIGH This Week

Denial of service in Quicly, the QUIC protocol library embedded in the H2O HTTP server, allows remote attackers to corrupt connection state and crash the process prior to commit 8b178e6. Quicly's packet decoder accepts Connection IDs up to 255 bytes (permitted for unknown QUIC versions) but its version-1 CID buffers are only 20 bytes, and the library - unlike its bundled CLI - never rejected over-length CIDs, letting an oversized CID overrun the buffer within its allocated chunk and trigger assertion failures. No public exploit is identified at time of analysis, and the flaw is not listed in CISA KEV.

Buffer Overflow Denial Of Service Quicly H2O
NVD GitHub
CVSS 3.1
7.5
EPSS
0.3%
CVE-2026-44435 Jul 16, 22:39 HIGH This Week

Remote denial of service in quicly, the IETF QUIC implementation used by the H2O HTTP server, allows unauthenticated attackers to crash the process by sending more than 32KB of valid handshake messages over the CRYPTO stream within a single packet number space, tripping a reachable assertion (CWE-617). Affects all builds prior to commit 937d0e9. No public exploit identified at time of analysis and the flaw is not in CISA KEV, but the network-reachable, no-privilege nature makes it trivially triggerable once understood.

Denial Of Service Quicly H2O
NVD GitHub VulDB
CVSS 3.1
7.5
EPSS
0.3%
CVE-2026-44433 Jul 16, 22:23 HIGH This Week

Memory exhaustion in Quicly's QUIC flow control handling allows an unauthenticated remote peer to force disproportionate receive buffer allocation in the H2O HTTP server by sending STREAM frames containing a single byte placed at the maximum permitted stream offset. The library pre-allocates buffers up to the largest received offset to accommodate out-of-order delivery, so a handful of crafted packets can cause the server to allocate memory far exceeding what the transferred data warrants. Under H2O's default stream concurrency settings, this attack multiplies per-connection memory usage by roughly 4x, making memory exhaustion achievable at low bandwidth cost. No public exploit identified at time of analysis; EPSS is 0.25% (16th percentile) and CISA SSVC lists exploitation as 'none', suggesting no observed real-world abuse.

Denial Of Service Quicly H2O
NVD GitHub VulDB
CVSS 3.1
7.5
EPSS
0.2%
CVE-2026-55213 Jul 10, 20:49 HIGH This Week

Remote unauthenticated denial of service in the h2o HTTP server (all versions prior to commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1) allows an attacker to crash the server by sending a crafted QPACK instruction over HTTP/3. The flaw causes lib/http3/qpack.c to allocate an ~800 KB on-stack buffer via alloca, overflowing the default musl libc pthread stack and segfaulting on the guard page. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV; impact is limited to availability with no data exposure.

Denial Of Service H2O
NVD GitHub VulDB
CVSS 3.1
7.5
EPSS
0.3%
CVE-2023-44487 Oct 10, 14:15 LIB HIGH POC KEV PATCH THREAT Act Now

Denial of service against HTTP/2 server implementations allows remote unauthenticated attackers to exhaust server resources by rapidly opening and immediately canceling (RST_STREAM) large numbers of streams over a single connection, a technique dubbed the 'Rapid Reset' attack. The flaw is confirmed actively exploited (CISA KEV) following large-scale weaponization observed August through October 2023, with publicly available exploit code and an EPSS score of 94.45% placing it in the 100th percentile for likelihood of exploitation. Virtually every major HTTP/2 stack - including nghttp2, Netty, Envoy, and Eclipse Jetty - is affected.

Denial Of Service Apache Node.js Golang Apple +176
NVD GitHub Exploit-DB VulDB
CVSS 3.1
7.5
EPSS
94.4%
Threat
7.3
CVE-2026-45271 Aug 21, 21:00 MEDIUM This Month

Stack exhaustion in the Picotls minicrypto backend's custom ASN.1 validator allows an attacker who can supply crafted private-key material to crash any application that calls ptls_minicrypto_load_private_key() or the public ptls_asn1_validation() API on untrusted DER input. All Picotls versions prior to upstream commit c14231d80 are affected when the minicrypto backend is in use; applications using the libcrypto (OpenSSL) backend are immune because OpenSSL performs its own bounded DER parsing. No public exploit has been identified and no CISA KEV listing exists; CVSS 5.5 reflects a local, user-interaction-dependent denial-of-service with no code execution potential.

Denial Of Service OpenSSL H2O Picotls
NVD GitHub
CVSS 3.1
5.5
EPSS
0.1%
CVE-2026-44452 Jul 16, 23:16 MEDIUM This Month

Denial-of-service via malformed TLS/QUIC ClientHello in h2o HTTP server allows remote unauthenticated attackers to crash the server process by sending a zero-length SNI extension. The hostname-copy routine assumes NULL-termination on the empty SNI buffer (CWE-125 out-of-bounds read), reading beyond the allocation boundary and triggering a segmentation fault. No public exploit or active exploitation (CISA KEV) has been identified; the fix is available as an upstream commit but no confirmed tagged release exists at time of analysis.

Buffer Overflow Information Disclosure H2O
NVD GitHub VulDB
CVSS 3.1
5.9
EPSS
0.2%
CVE-2026-44434 Jul 16, 22:34 MEDIUM This Month

Stateless reset injection in Quicly, the IETF QUIC implementation embedded in the H2O HTTP server, allows an on-path network attacker to abruptly terminate any active QUIC connection by sending an all-zero packet. The root cause is that Quicly zero-initializes its four stateless reset token slots but never validates which slots hold legitimate peer-advertised tokens, causing the all-zero default to be accepted as a valid reset signal whenever the peer has advertised fewer than four tokens. No public exploit code or active exploitation has been identified at time of analysis; however, the attack is mechanically straightforward for any adversary already positioned on the network path.

Code Injection Quicly H2O
NVD GitHub VulDB
CVSS 3.1
5.3
EPSS
0.1%
CVE-2025-61684 Jan 19, 16:15 HIGH PATCH This Week

Quicly, an IETF QUIC protocol implementation, is susceptible to a denial-of-service attack prior to commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e. A remote attacker can exploit these bugs to trigger an assertion failure that crashes process using Quicly. [CVSS 7.5 HIGH]

Denial Of Service Quicly H2O
NVD GitHub
CVSS 3.1
7.5
EPSS
0.2%
CVE-2025-10769 Sep 21, 10:15 LOW POC Monitor

A vulnerability has been found in h2oai h2o-3 up to 3.46.08. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD GitHub VulDB
CVSS 4.0
2.1
EPSS
0.1%
CVE-2025-10768 Sep 21, 10:15 LOW POC Monitor

A flaw has been found in h2oai h2o-3 up to 3.46.08. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD GitHub VulDB
CVSS 4.0
2.1
EPSS
0.1%
CVE-2025-6544 Sep 21, 09:15 LIB CRITICAL POC PATCH Act Now

A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, allowing attackers to read arbitrary system files and execute arbitrary code. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

RCE Deserialization H2O
NVD GitHub
CVSS 3.0
9.8
EPSS
0.4%
CVE-2024-8616 Mar 20, 10:15 LIB HIGH POC This Week

In h2oai/h2o-3 version 3.46.0, the `/99/Models/{name}/json` endpoint allows for arbitrary file overwrite on the target server. Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
CVSS 3.0
8.2
EPSS
0.1%
CVE-2024-8062 Mar 20, 10:15 LIB HIGH POC This Week

A vulnerability in the typeahead endpoint of h2oai/h2o-3 version 3.46.0 allows for a denial of service. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
CVSS 3.1
7.5
EPSS
0.1%
CVE-2024-7768 Mar 20, 10:15 LIB HIGH POC This Week

A vulnerability in the `/3/ImportFiles` endpoint of h2oai/h2o-3 version 3.46.1 allows an attacker to cause a denial of service. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
CVSS 3.0
7.5
EPSS
0.1%
CVE-2024-7765 Mar 20, 10:15 LIB HIGH POC This Week

In h2oai/h2o-3 version 3.46.0.2, a vulnerability exists where uploading and repeatedly parsing a large GZIP file can cause a denial of service. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
CVSS 3.1
7.5
EPSS
0.2%
CVE-2024-6863 Mar 20, 10:15 LIB MEDIUM POC This Week

In h2oai/h2o-3 version 3.46.0, an endpoint exposing a custom EncryptionTool allows an attacker to encrypt any files on the target server with a key of their choosing. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
CVSS 3.0
6.5
EPSS
0.1%
CVE-2024-6854 Mar 20, 10:15 LIB HIGH POC This Month

In h2oai/h2o-3 version 3.46.0, the endpoint for exporting models does not restrict the export location, allowing an attacker to export a model to any file in the server's file structure, thereby. Rated high severity (CVSS 7.1), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
CVSS 3.0
7.1
EPSS
0.1%
CVE-2024-10572 Mar 20, 10:15 LIB HIGH POC This Week

In h2oai/h2o-3 version 3.46.0.1, the `run_tool` command exposes classes in the `water.tools` package through the `ast` parser. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RCE Denial Of Service Code Injection H2O
NVD
CVSS 3.0
7.5
EPSS
0.1%
CVE-2024-10553 Mar 20, 10:15 LIB CRITICAL POC PATCH Act Now

A vulnerability in the h2oai/h2o-3 REST API versions 3.46.0.4 allows unauthenticated remote attackers to execute arbitrary code via deserialization of untrusted data. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

RCE PostgreSQL Deserialization H2O
NVD GitHub
CVSS 3.0
9.8
EPSS
3.7%
CVE-2024-10550 Mar 20, 10:15 LIB HIGH POC This Week

A vulnerability in the `/3/ParseSetup` endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service (DoS) attack. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
CVSS 3.0
7.5
EPSS
0.1%
CVE-2024-10549 Mar 20, 10:15 LIB HIGH POC This Week

A vulnerability in the `/3/Parse` endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service (DoS) attack. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
CVSS 3.0
7.5
EPSS
0.1%
CVE-2024-45403 Oct 11, 15:15 HIGH PATCH This Week

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Denial Of Service H2O Dena
NVD GitHub
CVSS 3.1
7.5
EPSS
0.6%
CVE-2024-45397 Oct 11, 15:15 HIGH PATCH This Week

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Authentication Bypass H2O Dena
NVD GitHub
CVSS 3.1
7.5
EPSS
0.4%
CVE-2024-25622 Oct 11, 15:15 MEDIUM POC PATCH This Month

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available.

Information Disclosure H2O Dena
NVD GitHub
CVSS 3.1
4.3
EPSS
0.4%
CVE-2024-8862 Sep 14, 20:15 PyPI MEDIUM POC PATCH This Month

A vulnerability, which was classified as critical, has been found in h2oai h2o-3 3.46.0.4. Rated medium severity (CVSS 6.9), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD VulDB
CVSS 4.0
6.9
EPSS
1.3%
CVE-2024-45758 Sep 06, 16:15 LIB CRITICAL POC Act Now

H2O.ai H2O through 3.46.0.4 allows attackers to arbitrarily set the JDBC URL, leading to deserialization attacks, file reads, and command execution. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD GitHub
CVSS 3.1
9.1
EPSS
0.9%
CVE-2024-5979 Jun 27, 19:15 PyPI HIGH POC This Week

In h2oai/h2o-3 version 3.46.0, the `run_tool` command in the `rapids` component allows the `main` function of any class under the `water.tools` namespace to be called. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RCE Denial Of Service Code Injection H2O
NVD GitHub
CVSS 3.0
7.5
EPSS
0.8%
CVE-2024-5550 Jun 06, 19:16 PyPI MEDIUM POC This Month

In h2oai/h2o-3 version 3.40.0.4, an exposure of sensitive information vulnerability exists due to an arbitrary system path lookup feature. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Path Traversal H2O
NVD
CVSS 3.1
5.3
EPSS
0.8%
CVE-2024-1456 Apr 16, 00:15 HIGH POC This Week

An S3 bucket takeover vulnerability was identified in the h2oai/h2o-3 repository. Rated high severity (CVSS 7.1), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Authentication Bypass H2O
NVD
CVSS 3.0
7.1
EPSS
0.2%
CVE-2023-6569 Dec 14, 13:15 PyPI HIGH POC PATCH This Week

External Control of File Name or Path in h2oai/h2o-3. Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
CVSS 3.1
8.2
EPSS
0.7%
CVE-2023-50247 Dec 12, 20:15 HIGH PATCH This Week

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Allocation of Resources Without Limits vulnerability could allow attackers to exhaust system resources through uncontrolled allocation.

Denial Of Service H2O Dena
NVD GitHub
CVSS 3.1
7.5
EPSS
0.9%
CVE-2023-41337 Dec 12, 20:15 MEDIUM PATCH This Month

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated medium severity (CVSS 6.7), this vulnerability is low attack complexity.

Code Injection Jwt Attack H2O Dena
NVD GitHub
CVSS 3.1
6.7
EPSS
0.2%
CVE-2023-6038 Nov 16, 17:15 Maven HIGH POC This Week

A Local File Inclusion (LFI) vulnerability exists in the h2o-3 REST API, allowing unauthenticated remote attackers to read arbitrary files on the server with the permissions of the user running the. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Authentication Bypass H2O
NVD
CVSS 3.1
7.5
EPSS
4.3%
CVE-2023-6017 Nov 16, 17:15 HIGH POC This Week

H2O included a reference to an S3 bucket that no longer existed allowing an attacker to take over the S3 bucket URL. Rated high severity (CVSS 7.1), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
CVSS 3.1
7.1
EPSS
0.9%
CVE-2023-6013 Nov 16, 17:15 MEDIUM POC This Month

H2O is vulnerable to stored XSS vulnerability which can lead to a Local File Include attack. Rated medium severity (CVSS 5.4), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

XSS H2O
NVD
CVSS 3.1
5.4
EPSS
0.7%
CVE-2023-6016 Nov 16, 16:15 CRITICAL POC THREAT Act Now

An attacker is able to gain remote code execution on a server hosting the H2O dashboard through it's POJO model import feature. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RCE Code Injection H2O
NVD
CVSS 3.1
9.8
EPSS
30.6%
CVE-2023-30847 Apr 27, 15:15 HIGH PATCH This Week

H2O is an HTTP server. Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Denial Of Service Memory Corruption H2O Dena
NVD GitHub
CVSS 3.1
8.2
EPSS
0.9%
CVE-2018-0608 Jun 26, 14:29 CRITICAL Act Now

Buffer overflow in H2O version 2.2.4 and earlier allows remote attackers to execute arbitrary code or cause a denial of service (DoS) via unspecified vectors. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

RCE Buffer Overflow Denial Of Service H2O Dena
NVD GitHub
CVSS 3.0
9.8
EPSS
3.8%
CVE-2017-10908 Dec 22, 14:29 HIGH This Week

H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via specially crafted HTTP/2 header. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

Denial Of Service H2O Dena
NVD GitHub
CVSS 3.0
7.5
EPSS
1.3%
CVE-2017-10872 Dec 22, 14:29 MEDIUM This Month

H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via unspecified vectors. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.

Denial Of Service H2O Dena
NVD GitHub
CVSS 3.0
6.5
EPSS
0.7%
CVE-2017-10869 Dec 22, 14:29 HIGH This Week

Buffer overflow in H2O version 2.2.2 and earlier allows remote attackers to cause a denial-of-service in the server via unspecified vectors. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

Buffer Overflow H2O Dena
NVD GitHub
CVSS 3.0
7.5
EPSS
1.9%
CVE-2017-10868 Dec 22, 14:29 HIGH This Week

H2O version 2.2.2 and earlier allows remote attackers to cause a denial of service in the server via specially crafted HTTP/1 header. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

Denial Of Service H2O Dena
NVD GitHub
CVSS 3.1
7.5
EPSS
1.2%
CVE-2016-7835 Jun 09, 16:29 CRITICAL PATCH Act Now

Use-after-free vulnerability in H2O allows remote attackers to cause a denial-of-service (DoS) or obtain server certificate private keys and possibly other information. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Use After Free vulnerability could allow attackers to access freed memory to execute arbitrary code or crash the application.

Information Disclosure Use After Free Memory Corruption H2O Dena
NVD GitHub
CVSS 3.0
9.1
EPSS
3.2%
CVE-2016-4864 May 12, 18:29 HIGH PATCH This Week

H2O versions 2.0.3 and earlier and 2.1.0-beta2 and earlier allows remote attackers to cause a denial-of-service (DoS) via format string specifiers in a template file via fastcgi, mruby, proxy,. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Information Disclosure H2O Dena
NVD GitHub
CVSS 3.0
7.5
EPSS
1.6%
CVE-2016-4817 Jun 19, 01:59 HIGH This Week

lib/http2/connection.c in H2O before 1.7.3 and 2.x before 2.0.0-beta5 mishandles HTTP/2 disconnection, which allows remote attackers to cause a denial of service (use-after-free and application. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

RCE Denial Of Service H2O Dena
NVD GitHub
CVSS 3.0
7.5
EPSS
8.0%
CVE-2016-1133 Jan 16, 05:59 LOW Monitor

CRLF injection vulnerability in the on_req function in lib/handler/redirect.c in H2O before 1.6.2 and 1.7.x before 1.7.0-beta3 allows remote attackers to inject arbitrary HTTP headers and conduct. Rated low severity (CVSS 3.7), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.

Code Injection H2O Dena
NVD GitHub
CVSS 3.0
3.7
EPSS
0.4%
EPSS 0% CVSS 7.5
HIGH This Week

Remote denial of service in the h2o HTTP server (all versions prior to commit 9265bdd) allows unauthenticated attackers to exhaust server memory by combining HPACK header-decompression amplification with Slowloris-style HTTP/2 stream stalling. By opening many streams that stall mid-request, an attacker forces the server to retain large volumes of amplified decoded header state, degrading or crashing the service. There is no public exploit identified at time of analysis, and the CVSS 7.5 (A:H only) reflects an availability-only impact with no confidentiality or integrity effect.

Denial Of Service H2O
NVD GitHub VulDB
EPSS 0% CVSS 7.5
HIGH This Week

Denial of service in the h2o HTTP server (all versions prior to commit 6b5370d) allows remote unauthenticated attackers to crash the server by requesting static files whose on-stack path construction via alloca can reach ~600KB, exceeding musl libc's default 128KB pthread stack and triggering a guard-page segmentation fault. The flaw is a CWE-770 uncontrolled resource allocation issue affecting availability only (CVSS 7.5, A:H). There is no public exploit identified at time of analysis and it is not listed in CISA KEV, but exploitation is trivial where h2o is built against musl libc.

Denial Of Service H2O
NVD GitHub VulDB
EPSS 0% CVSS 7.5
HIGH This Week

Denial of service in Quicly, the QUIC protocol library embedded in the H2O HTTP server, allows remote attackers to corrupt connection state and crash the process prior to commit 8b178e6. Quicly's packet decoder accepts Connection IDs up to 255 bytes (permitted for unknown QUIC versions) but its version-1 CID buffers are only 20 bytes, and the library - unlike its bundled CLI - never rejected over-length CIDs, letting an oversized CID overrun the buffer within its allocated chunk and trigger assertion failures. No public exploit is identified at time of analysis, and the flaw is not listed in CISA KEV.

Buffer Overflow Denial Of Service Quicly +1
NVD GitHub
EPSS 0% CVSS 7.5
HIGH This Week

Remote denial of service in quicly, the IETF QUIC implementation used by the H2O HTTP server, allows unauthenticated attackers to crash the process by sending more than 32KB of valid handshake messages over the CRYPTO stream within a single packet number space, tripping a reachable assertion (CWE-617). Affects all builds prior to commit 937d0e9. No public exploit identified at time of analysis and the flaw is not in CISA KEV, but the network-reachable, no-privilege nature makes it trivially triggerable once understood.

Denial Of Service Quicly H2O
NVD GitHub VulDB
EPSS 0% CVSS 7.5
HIGH This Week

Memory exhaustion in Quicly's QUIC flow control handling allows an unauthenticated remote peer to force disproportionate receive buffer allocation in the H2O HTTP server by sending STREAM frames containing a single byte placed at the maximum permitted stream offset. The library pre-allocates buffers up to the largest received offset to accommodate out-of-order delivery, so a handful of crafted packets can cause the server to allocate memory far exceeding what the transferred data warrants. Under H2O's default stream concurrency settings, this attack multiplies per-connection memory usage by roughly 4x, making memory exhaustion achievable at low bandwidth cost. No public exploit identified at time of analysis; EPSS is 0.25% (16th percentile) and CISA SSVC lists exploitation as 'none', suggesting no observed real-world abuse.

Denial Of Service Quicly H2O
NVD GitHub VulDB
EPSS 0% CVSS 7.5
HIGH This Week

Remote unauthenticated denial of service in the h2o HTTP server (all versions prior to commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1) allows an attacker to crash the server by sending a crafted QPACK instruction over HTTP/3. The flaw causes lib/http3/qpack.c to allocate an ~800 KB on-stack buffer via alloca, overflowing the default musl libc pthread stack and segfaulting on the guard page. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV; impact is limited to availability with no data exposure.

Denial Of Service H2O
NVD GitHub VulDB
EPSS 94% 7.3 CVSS 7.5
HIGH POC KEV PATCH THREAT Act Now

Denial of service against HTTP/2 server implementations allows remote unauthenticated attackers to exhaust server resources by rapidly opening and immediately canceling (RST_STREAM) large numbers of streams over a single connection, a technique dubbed the 'Rapid Reset' attack. The flaw is confirmed actively exploited (CISA KEV) following large-scale weaponization observed August through October 2023, with publicly available exploit code and an EPSS score of 94.45% placing it in the 100th percentile for likelihood of exploitation. Virtually every major HTTP/2 stack - including nghttp2, Netty, Envoy, and Eclipse Jetty - is affected.

Denial Of Service Apache Node.js +178
NVD GitHub Exploit-DB VulDB
EPSS 0% CVSS 5.5
MEDIUM This Month

Stack exhaustion in the Picotls minicrypto backend's custom ASN.1 validator allows an attacker who can supply crafted private-key material to crash any application that calls ptls_minicrypto_load_private_key() or the public ptls_asn1_validation() API on untrusted DER input. All Picotls versions prior to upstream commit c14231d80 are affected when the minicrypto backend is in use; applications using the libcrypto (OpenSSL) backend are immune because OpenSSL performs its own bounded DER parsing. No public exploit has been identified and no CISA KEV listing exists; CVSS 5.5 reflects a local, user-interaction-dependent denial-of-service with no code execution potential.

Denial Of Service OpenSSL H2O +1
NVD GitHub
EPSS 0% CVSS 5.9
MEDIUM This Month

Denial-of-service via malformed TLS/QUIC ClientHello in h2o HTTP server allows remote unauthenticated attackers to crash the server process by sending a zero-length SNI extension. The hostname-copy routine assumes NULL-termination on the empty SNI buffer (CWE-125 out-of-bounds read), reading beyond the allocation boundary and triggering a segmentation fault. No public exploit or active exploitation (CISA KEV) has been identified; the fix is available as an upstream commit but no confirmed tagged release exists at time of analysis.

Buffer Overflow Information Disclosure H2O
NVD GitHub VulDB
EPSS 0% CVSS 5.3
MEDIUM This Month

Stateless reset injection in Quicly, the IETF QUIC implementation embedded in the H2O HTTP server, allows an on-path network attacker to abruptly terminate any active QUIC connection by sending an all-zero packet. The root cause is that Quicly zero-initializes its four stateless reset token slots but never validates which slots hold legitimate peer-advertised tokens, causing the all-zero default to be accepted as a valid reset signal whenever the peer has advertised fewer than four tokens. No public exploit code or active exploitation has been identified at time of analysis; however, the attack is mechanically straightforward for any adversary already positioned on the network path.

Code Injection Quicly H2O
NVD GitHub VulDB
EPSS 0% CVSS 7.5
HIGH PATCH This Week

Quicly, an IETF QUIC protocol implementation, is susceptible to a denial-of-service attack prior to commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e. A remote attacker can exploit these bugs to trigger an assertion failure that crashes process using Quicly. [CVSS 7.5 HIGH]

Denial Of Service Quicly H2O
NVD GitHub
EPSS 0% CVSS 2.1
LOW POC Monitor

A vulnerability has been found in h2oai h2o-3 up to 3.46.08. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD GitHub VulDB
EPSS 0% CVSS 2.1
LOW POC Monitor

A flaw has been found in h2oai h2o-3 up to 3.46.08. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD GitHub VulDB
EPSS 0% CVSS 9.8
CRITICAL POC PATCH Act Now

A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, allowing attackers to read arbitrary system files and execute arbitrary code. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

RCE Deserialization H2O
NVD GitHub
EPSS 0% CVSS 8.2
HIGH POC This Week

In h2oai/h2o-3 version 3.46.0, the `/99/Models/{name}/json` endpoint allows for arbitrary file overwrite on the target server. Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
EPSS 0% CVSS 7.5
HIGH POC This Week

A vulnerability in the typeahead endpoint of h2oai/h2o-3 version 3.46.0 allows for a denial of service. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
EPSS 0% CVSS 7.5
HIGH POC This Week

A vulnerability in the `/3/ImportFiles` endpoint of h2oai/h2o-3 version 3.46.1 allows an attacker to cause a denial of service. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
EPSS 0% CVSS 7.5
HIGH POC This Week

In h2oai/h2o-3 version 3.46.0.2, a vulnerability exists where uploading and repeatedly parsing a large GZIP file can cause a denial of service. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
EPSS 0% CVSS 6.5
MEDIUM POC This Week

In h2oai/h2o-3 version 3.46.0, an endpoint exposing a custom EncryptionTool allows an attacker to encrypt any files on the target server with a key of their choosing. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
EPSS 0% CVSS 7.1
HIGH POC This Month

In h2oai/h2o-3 version 3.46.0, the endpoint for exporting models does not restrict the export location, allowing an attacker to export a model to any file in the server's file structure, thereby. Rated high severity (CVSS 7.1), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
EPSS 0% CVSS 7.5
HIGH POC This Week

In h2oai/h2o-3 version 3.46.0.1, the `run_tool` command exposes classes in the `water.tools` package through the `ast` parser. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RCE Denial Of Service Code Injection +1
NVD
EPSS 4% CVSS 9.8
CRITICAL POC PATCH Act Now

A vulnerability in the h2oai/h2o-3 REST API versions 3.46.0.4 allows unauthenticated remote attackers to execute arbitrary code via deserialization of untrusted data. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

RCE PostgreSQL Deserialization +1
NVD GitHub
EPSS 0% CVSS 7.5
HIGH POC This Week

A vulnerability in the `/3/ParseSetup` endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service (DoS) attack. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
EPSS 0% CVSS 7.5
HIGH POC This Week

A vulnerability in the `/3/Parse` endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service (DoS) attack. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Denial Of Service H2O
NVD
EPSS 1% CVSS 7.5
HIGH PATCH This Week

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Denial Of Service H2O Dena
NVD GitHub
EPSS 0% CVSS 7.5
HIGH PATCH This Week

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Authentication Bypass H2O Dena
NVD GitHub
EPSS 0% CVSS 4.3
MEDIUM POC PATCH This Month

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated medium severity (CVSS 4.3), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available.

Information Disclosure H2O Dena
NVD GitHub
EPSS 1% CVSS 6.9
MEDIUM POC PATCH This Month

A vulnerability, which was classified as critical, has been found in h2oai h2o-3 3.46.0.4. Rated medium severity (CVSS 6.9), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD VulDB
EPSS 1% CVSS 9.1
CRITICAL POC Act Now

H2O.ai H2O through 3.46.0.4 allows attackers to arbitrarily set the JDBC URL, leading to deserialization attacks, file reads, and command execution. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Deserialization H2O
NVD GitHub
EPSS 1% CVSS 7.5
HIGH POC This Week

In h2oai/h2o-3 version 3.46.0, the `run_tool` command in the `rapids` component allows the `main` function of any class under the `water.tools` namespace to be called. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RCE Denial Of Service Code Injection +1
NVD GitHub
EPSS 1% CVSS 5.3
MEDIUM POC This Month

In h2oai/h2o-3 version 3.40.0.4, an exposure of sensitive information vulnerability exists due to an arbitrary system path lookup feature. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Path Traversal H2O
NVD
EPSS 0% CVSS 7.1
HIGH POC This Week

An S3 bucket takeover vulnerability was identified in the h2oai/h2o-3 repository. Rated high severity (CVSS 7.1), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Authentication Bypass H2O
NVD
EPSS 1% CVSS 8.2
HIGH POC PATCH This Week

External Control of File Name or Path in h2oai/h2o-3. Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
EPSS 1% CVSS 7.5
HIGH PATCH This Week

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Allocation of Resources Without Limits vulnerability could allow attackers to exhaust system resources through uncontrolled allocation.

Denial Of Service H2O Dena
NVD GitHub
EPSS 0% CVSS 6.7
MEDIUM PATCH This Month

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Rated medium severity (CVSS 6.7), this vulnerability is low attack complexity.

Code Injection Jwt Attack H2O +1
NVD GitHub
EPSS 4% CVSS 7.5
HIGH POC This Week

A Local File Inclusion (LFI) vulnerability exists in the h2o-3 REST API, allowing unauthenticated remote attackers to read arbitrary files on the server with the permissions of the user running the. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Authentication Bypass H2O
NVD
EPSS 1% CVSS 7.1
HIGH POC This Week

H2O included a reference to an S3 bucket that no longer existed allowing an attacker to take over the S3 bucket URL. Rated high severity (CVSS 7.1), this vulnerability is no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Information Disclosure H2O
NVD
EPSS 1% CVSS 5.4
MEDIUM POC This Month

H2O is vulnerable to stored XSS vulnerability which can lead to a Local File Include attack. Rated medium severity (CVSS 5.4), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available and no vendor patch available.

XSS H2O
NVD
EPSS 31% CVSS 9.8
CRITICAL POC THREAT Act Now

An attacker is able to gain remote code execution on a server hosting the H2O dashboard through it's POJO model import feature. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RCE Code Injection H2O
NVD
EPSS 1% CVSS 8.2
HIGH PATCH This Week

H2O is an HTTP server. Rated high severity (CVSS 8.2), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Denial Of Service Memory Corruption H2O +1
NVD GitHub
EPSS 4% CVSS 9.8
CRITICAL Act Now

Buffer overflow in H2O version 2.2.4 and earlier allows remote attackers to execute arbitrary code or cause a denial of service (DoS) via unspecified vectors. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

RCE Buffer Overflow Denial Of Service +2
NVD GitHub
EPSS 1% CVSS 7.5
HIGH This Week

H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via specially crafted HTTP/2 header. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

Denial Of Service H2O Dena
NVD GitHub
EPSS 1% CVSS 6.5
MEDIUM This Month

H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via unspecified vectors. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.

Denial Of Service H2O Dena
NVD GitHub
EPSS 2% CVSS 7.5
HIGH This Week

Buffer overflow in H2O version 2.2.2 and earlier allows remote attackers to cause a denial-of-service in the server via unspecified vectors. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

Buffer Overflow H2O Dena
NVD GitHub
EPSS 1% CVSS 7.5
HIGH This Week

H2O version 2.2.2 and earlier allows remote attackers to cause a denial of service in the server via specially crafted HTTP/1 header. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

Denial Of Service H2O Dena
NVD GitHub
EPSS 3% CVSS 9.1
CRITICAL PATCH Act Now

Use-after-free vulnerability in H2O allows remote attackers to cause a denial-of-service (DoS) or obtain server certificate private keys and possibly other information. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This Use After Free vulnerability could allow attackers to access freed memory to execute arbitrary code or crash the application.

Information Disclosure Use After Free Memory Corruption +2
NVD GitHub
EPSS 2% CVSS 7.5
HIGH PATCH This Week

H2O versions 2.0.3 and earlier and 2.1.0-beta2 and earlier allows remote attackers to cause a denial-of-service (DoS) via format string specifiers in a template file via fastcgi, mruby, proxy,. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

Information Disclosure H2O Dena
NVD GitHub
EPSS 8% CVSS 7.5
HIGH This Week

lib/http2/connection.c in H2O before 1.7.3 and 2.x before 2.0.0-beta5 mishandles HTTP/2 disconnection, which allows remote attackers to cause a denial of service (use-after-free and application. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

RCE Denial Of Service H2O +1
NVD GitHub
EPSS 0% CVSS 3.7
LOW Monitor

CRLF injection vulnerability in the on_req function in lib/handler/redirect.c in H2O before 1.6.2 and 1.7.x before 1.7.0-beta3 allows remote attackers to inject arbitrary HTTP headers and conduct. Rated low severity (CVSS 3.7), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.

Code Injection H2O Dena
NVD GitHub

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