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curl CVE-2026-9545

| EUVDEUVD-2026-41493 HIGH
Information Exposure (CWE-200)
7.5
CVSS 3.1 · Vendor
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Severity by source

Vendor (CNA) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
vuln.today AI
3.7 LOW

Active MITM plus non-default early-data opt-in raises complexity to AC:H; no client auth so PR:N; only request data leaks, giving C:H with I:N/A:N.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
SUSE
5.9 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (CNA).

CVSS VectorVendor

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Lifecycle Timeline

7
Analysis Updated
Jul 06, 2026 - 18:50 vuln.today
v5 (cvss_changed)
Analysis Updated
Jul 06, 2026 - 18:49 vuln.today
v4 (cvss_changed)
Analysis Updated
Jul 06, 2026 - 18:47 vuln.today
v3 (cvss_changed)
Analysis Updated
Jul 06, 2026 - 18:46 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Jul 06, 2026 - 18:22 vuln.today
cvss_changed
CVSS changed
Jul 06, 2026 - 18:22 NVD
7.5 (HIGH)
Analysis Generated
Jun 24, 2026 - 18:26 vuln.today

Description PRE-NVD

Disclosed via oss-security. NVD scoring and full description are pending.

AnalysisAI

Information disclosure in libcurl (curl 8.11.0 through 8.20.0) allows a network man-in-the-middle to capture sensitive request data when TLS early data (0-RTT) is combined with SSL session ID caching. If an application enables the CURLSSLOPT_EARLYDATA bit and leaves the session cache active, libcurl can transmit a resumed request's bytes on a reconnection before it enforces a certificate verification failure, so an attacker who impersonates the original host without a valid certificate may receive the leaked data. No public exploit identified at time of analysis, and EPSS is low (0.13%), reflecting the non-default configuration and active-MITM prerequisite.

Technical ContextAI

The flaw lives in libcurl's TLS session resumption path when TLS 1.3 early data (0-RTT) is used. TLS 0-RTT lets a client send application bytes in the first flight using a pre-shared key derived from a previously cached session, before the fresh handshake completes - and thus before the server's certificate is re-validated. libcurl gates this behind two opt-ins: CURLOPT_SSL_SESSIONID_CACHE (session cache, on by default) and the CURLSSLOPT_EARLYDATA bit inside CURLOPT_SSL_OPTIONS (off by default). The bug is an ordering/error-handling defect: on the second connection to a host now controlled by an impostor lacking a valid certificate, libcurl emits the early-data payload before the certificate verification failure aborts the transfer. No CWE was assigned by NVD, but the root cause is best classed as improper certificate validation prior to data transmission (CWE-295 family), specifically a check-after-use ordering error. Affected CPEs span curl/libcurl across the 8.11.x-8.20.x line per the ENISA EUVD data.

RemediationAI

Patch available per vendor advisory - upgrade to the fixed curl/libcurl release identified at https://curl.se/docs/CVE-2026-9545.html (a released patched version tag is not independently confirmed in the input, so consult the advisory for the exact fixed version), and on Ubuntu apply the packages from USN-8487-1 (https://ubuntu.com/security/notices/USN-8487-1). If immediate patching is not possible, the most direct compensating control is to disable TLS early data by clearing the CURLSSLOPT_EARLYDATA bit in CURLOPT_SSL_OPTIONS, which fully removes the 0-RTT leak path at the cost of losing the round-trip latency savings of early data. Alternatively, disabling the session cache via CURLOPT_SSL_SESSIONID_CACHE prevents the resumption that enables 0-RTT, but increases full-handshake overhead on repeat connections. Because the attack also depends on an active MITM, hardening the network path (certificate pinning where feasible, trusted DNS/DoH to resist redirection) reduces the opportunity for host impersonation, though these do not fix the underlying ordering bug.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SLES15-SP5-CHOST-BYOS-SAP-CCloud Affected
SLES15-SP6-CHOST-BYOS Affected
SLES15-SP6-CHOST-BYOS-Aliyun Affected
SLES15-SP6-CHOST-BYOS-Azure Affected
SLES15-SP6-CHOST-BYOS-EC2 Affected

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CVE-2026-9545 vulnerability details – vuln.today

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