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  4. CVE 2026 66034 libssh2 heap out of bounds read via publickey
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Back to active CVEs
High · CVSS 7.7CVE-2026-66034

libssh2 Heap Out-of-Bounds Read via publickey subsystemCVE-2026-66034

Answer in brief

CVE-2026-66034 records a High severity (CVSS 7.7) vulnerability in libssh2 Heap Out-of-Bounds Read via publickey subsystem. The current sources do not mark it as known exploited. The current feed maps libssh2/libssh2 (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jul 24, 2026Updated Nov 10, 2026Source checked Nov 10, 2026First seen by HOL Nov 8, 2026Material review Nov 10, 2026
Upstream Advisory

Record context

Vulnerability class
Buffer Overflow
EPSS
Not reported
CWE IDs
CWE-125, CWE-908
Source
CVE List V5
Source checked
Nov 10, 2026
References
4 linked sources
Open source record

Key facts

Risk
High · CVSS 7.7
Exploitation
Not marked as known exploited
Affected software
7 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 7.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps libssh2/libssh2 (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.

Affected products and reported versions
ProductAffected versionsFixed versions
cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:*Not reportedNot reported
Mapped affected packages and fixed versions
PackageAffected rangeFixed version
libssh2/libssh2generic>=0 <=1.11.1Not reported
Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)generic>=V3.1.7 <**
Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0)generic>=V3.1.7 <**
Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0)generic>=V3.1.7 <**
Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0)generic>=V3.1.7 <**
Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)generic>=V3.1.7 <**

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for libssh2/libssh2, Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0).
  2. 2Review the reported fix. Update Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) to *; Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) to *; Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) to *; Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) to *; Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) to * if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

  1. Published upstream

    Jul 24, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Nov 10, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Nov 8, 2026

Sources and claim methodology

  • Source referencecert-portal.siemens.com
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • Source referencevulncheck.com
Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.