Skip to main content

Libssh2 CVE-2026-66035

| EUVDEUVD-2026-48722 HIGH
Heap-based Buffer Overflow (CWE-122)
2026-07-24 VulnCheck GHSA-v6rf-8q4r-r495
Buffer Overflow Heap Overflow Red Hat Suse Libssh2
7.7
CVSS 4.0 · Vendor: VulnCheck
View

Vulnerability Assessment

Weakness
CWE
CWE-122
ASVS 5.0
V15 - Secure Coding and Architecture Heap buffer bounds checking
MITRE ATT&CK

1 technique across 1 tactic: Execution

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Sign in to read
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.3% exploitation probability (EPSS)

Get an e-mail when this CVE is exploited, patched or re-scored. Free account.

Alert me

AnalysisAIv1 – Jul 26, 2026

Pre-authentication remote code execution in libssh2 1.11.1 and earlier allows a malicious SSH server to compromise any connecting client. A heap buffer overflow in the Encrypt-then-MAC (ETM) cipher negotiation path overwrites heap metadata, enabling tcache bin confusion and function pointer control before user authentication. No active exploitation is known, and EPSS is low (0.32%), but the client-side impact is severe if a victim can be lured to an attacker-controlled server.

Affected VersionsENISA

libssh2 patch: 42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4
libssh2 0 ≤1.11.1

Affected Packages

euvd libssh2 no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Sign in to check

Know when Libssh2 gets its next vulnerability

  • Watch products and get an email when something new is published
  • Check this CVE against your own stack and servers
  • Exploit and PoC references, threat intelligence from 22 sources
Continue with Google Continue with GitHub

No credit card · 7-day full trial

Severity by source

Vendor (VulnCheck) PRIMARY 7.7 HIGH
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
SUSE 7.5 HIGH
AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Red Hat 5.3 MEDIUM

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
High
Attack Requirements
None
Privileges Required
None
User Interaction
Passive
Vulnerable system: Confidentiality
High
Vulnerable system: Integrity
High
Vulnerable system: Availability
High
Subsequent system: Confidentiality
None
Subsequent system: Integrity
None
Subsequent system: Availability
None

DescriptionCVE.org

libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.

Threat Intelligence Overview

EPSS Score
0.3%
Top 76% exploitable
Social Media
1
Sightings
Data Quality
8 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment MSRC Vendor CIRCL GitHub VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.3%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact· derived
Medium
Technical Impact
Total

Priority Score

38
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +38
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Heap Overflow HIGH

A heap overflow occurs when a program writes data beyond the bounds of a buffer allocated in the heap memory region.

More in Libssh2

View all
CVE-2023-48795 MEDIUM POC
5.9 Dec 18

The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6 and other products, allows remot
CVE-2026-55200 CRITICAL POC
9.2 Jun 17

Remote code execution in libssh2 through version 1.11.1 stems from an unchecked packet_length field in ssh2_transport_re
CVE-2019-17498 HIGH POC
8.1 Oct 21

In libssh2 v1.9.0 and earlier versions, the SSH_MSG_DISCONNECT logic in packet.c has an integer overflow in a bounds che
CVE-2026-58050 HIGH POC
8.3 Jun 28

Heap buffer overflow in the libssh2 SSH client library (all versions through 1.11.1) lets a malicious or compromised SSH
CVE-2026-58051 HIGH POC
8.3 Jun 28

Free of an uninitialized, attacker-influenceable pointer in libssh2 through 1.11.1 allows a malicious SSH server to corr
CVE-2025-15661 HIGH POC
8.3 Jun 18

Out-of-bounds heap read in libssh2 through 1.11.1 enables a malicious SFTP server or man-in-the-middle attacker to leak

CVE-2019-13115 HIGH POC
8.1 Jul 16

In libssh2 before 1.9.0, kex_method_diffie_hellman_group_exchange_sha256_key_exchange in kex.c has an integer overflow t
CVE-2019-3862 CRITICAL
9.1 Mar 21

An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the way SSH_MSG_CHANNEL_REQUEST packets with an exi
CVE-2019-3855 HIGH
8.8 Mar 21

An integer overflow flaw which could lead to an out of bounds write was discovered in libssh2 before 1.8.1 in the way pa
CVE-2019-3858 CRITICAL
9.1 Mar 21

An out of bounds read flaw was discovered in libssh2 before 1.8.1 when a specially crafted SFTP packet is received from

CVE-2019-3859 CRITICAL
9.1 Mar 21

An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the _libssh2_packet_require and _libssh2_packet_req
CVE-2019-3861 CRITICAL
9.1 Mar 25

An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the way SSH packets with a padding length value gre

Same weakness CWE-122 – Heap-based Buffer Overflow

View all
CVE-2023-4911 HIGH POC
7.8
CVE-2023-27997 CRITICAL
9.8
CVE-2026-94127 CRITICAL POC
9.3
CVE-2025-25249 CRITICAL POC
9.8
CVE-2026-85880 HIGH POC
7.8
CVE-2025-24985 HIGH POC
7.8
CVE-2026-53362 HIGH POC
7.8
CVE-2025-21418 HIGH
7.8

Same technique Buffer Overflow

View all
CVE-2017-7269 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2015-3113 CRITICAL POC
9.8
CVE-2011-2462 CRITICAL POC
9.8
CVE-2020-0796 CRITICAL POC
10.0
CVE-2019-11043 CRITICAL POC
9.8
CVE-2009-0927 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8

Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected
SUSE Linux Enterprise Micro 5.3 Affected

References

Advisories & patches
PATCH https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4 ADVISORY https://access.redhat.com/errata/RHSA-2026:46955 ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-66035 ADVISORY https://ubuntu.com/security/notices/USN-8722-1 ADVISORY https://vuldb.com/vuln/382987 REF https://github.com/libssh2/libssh2/pull/2198 REF https://www.vulncheck.com/advisories/libssh2-heap-buffer-overflow-via-etm-cipher-negotiation

Search Externally

GitHub PoC Exploit-DB PacketStorm Snyk Rapid7 Nuclei Templates Trickest PoC
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy