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Libssh2 CVE-2026-66034

| EUVDEUVD-2026-48721 HIGH
Out-of-bounds Read (CWE-125)
2026-07-24 VulnCheck GHSA-6h6q-9mwg-r6x7
Buffer Overflow Information Disclosure Red Hat Suse Libssh2
7.7
CVSS 4.0 · Vendor: VulnCheck
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Vulnerability Assessment

Weakness
CWE
CWE-125
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, read limits
MITRE ATT&CK

1 technique across 1 tactic: Collection

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

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

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AnalysisAIv2 – Jul 26, 2026

Memory corruption in libssh2's publickey response parser allows a malicious SSH server to leak heap pointers and corrupt the heap, potentially leading to remote code execution. The issue affects libssh2 versions up to 1.11.1 and is triggered when a client connects to an attacker-controlled SSH server and fetches public keys, with no authentication required on the server side. A patch is available in commit a13bb6c, though no tagged release includes the fix yet; no active exploitation or public exploit code is currently reported.

Earlier versions of this analysis (1)
v1 Jul 26, 2026 - 12:04 CVSS 7.7

Heap out-of-bounds read and memory corruption in libssh2 up to version 1.11.1 allows a malicious SSH server to leak heap data and potentially execute arbitrary code on an unsuspecting client. The flaw resides in the publickey subsystem's response parser, which fails to validate a server-controlled length field before advancing a buffer pointer, leading to an arbitrary-length read and subsequent free of an uninitialized pointer. No active exploitation is currently documented, and the probability of widespread exploitation is relatively low based on EPSS and SSVC assessments.

Affected VersionsENISA

libssh2 patch: a13bb6c773f0d55ad1628cede57e99803cd898d9
libssh2 0 ≤1.11.1

Affected Packages

euvd libssh2 no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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  • Exploit and PoC references, threat intelligence from 22 sources
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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 5.9 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 a13bb6c, contains a missing bounds check vulnerability that allows a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1 response parser reads a server-controlled comment_len value and advances the parse pointer without verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup path frees an uninitialized pointer from a non-zeroed realloc() region.

Threat Intelligence Overview

EPSS Score
0.3%
Top 83% 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.

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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Same weakness CWE-125 – Out-of-bounds Read

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Same technique Buffer Overflow

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CVE-2015-5119 CRITICAL POC
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CVE-2015-3113 CRITICAL POC
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CVE-2011-2462 CRITICAL POC
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CVE-2020-0796 CRITICAL POC
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CVE-2019-11043 CRITICAL POC
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CVE-2009-0927 HIGH POC
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CVE-2012-1889 HIGH POC
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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/a13bb6c773f0d55ad1628cede57e99803cd898d9 ADVISORY https://access.redhat.com/errata/RHSA-2026:46927 ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-66034 ADVISORY https://ubuntu.com/security/notices/USN-8799-1 ADVISORY https://vuldb.com/vuln/382986 REF https://github.com/libssh2/libssh2/pull/2202 REF https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem

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