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TI-2026-47023 Aliases CVE-2026-66034GHSA-6h6q-9mwg-r6x7

libssh2 Heap Out-of-Bounds Read via publickey subsystem

Priority LOW 36CWE-125Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Passive
Attack complexity
High
Attack requirements
None
Impact type
—
Confidentiality · integrity · availability
High · High · High
Fix status
Partial Red Hat: 2 fixed, 1 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00402 34th percentileScored 2026-11-07
Fix Partial Red Hat: 2 advisoriesRed Hat: 2 fixed, 1 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
The libssh2 Projectlibssh2up to 1.11.1—Patch availableCNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:*up to 1.11.1VulnerableThe libssh2 Project
  • cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:* Versions up to 1.11.1 Vulnerable ·The libssh2 Project

Remediation

Red Hat 2 advisories

  • RHSA-2026:61752 Released 2026-08-31 · Red Hat rating Important
    libssh2 security update
    • Red Hat Enterprise Linux Server (v. 7 ELS) libssh2-1.8.0-4.el7_9.2, libssh2-1.8.0-4.el7_9.2.ppc
    • Red Hat Enterprise Linux Server Optional (v. 7 ELS) libssh2-devel-1.8.0-4.el7_9.2, libssh2-devel-1.8.0-4.el7_9.2.ppc
  • RHSA-2026:46927 Released 2026-07-27 · Red Hat rating Important
    Red Hat Hardened Images RPMs Security Update
    • Red Hat Hardened Images libssh2-1.11.1-10.2.hum1@aarch64, libssh2-1.11.1-10.2.hum1@src, libssh2-1.11.1-10.2.hum1@x86_64 +4

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux 6AffectedNo fix planned: Out of support scope
Red Hat Enterprise Linux Server (v. 7 ELS)Fixed RHSA-2026:61752
Red Hat Hardened ImagesFixed RHSA-2026:46927
Not affected: 2 products
  • Red Hat Enterprise Linux Server (v. 7 ELS)
  • Red Hat Enterprise Linux Server Optional (v. 7 ELS)

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-66034
  2. 2026-10-03 Alias added: GHSA-6h6q-9mwg-r6x7

References

Patch 2

  • TI-2026-39880 libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c CVSS 4.0CRITICAL 9.2
  • TI-2026-06681 libssh2 userauth.c userauth_password integer overflow CVSS 4.0MEDIUM 6.9
  • TI-2023-26623 The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6… CVSS 3.1MEDIUM 5.9
  • TI-2026-41806 libssh2 - Free of Uninitialized Pointer in publickey List Cleanup CVSS 4.0HIGH 8.3
  • TI-2019-02869 Out-of-bounds read in libssh2 CVSS 3.1CRITICAL 9.1
  • TI-2019-02865 Integer overflow in libssh2 CVSS 3.1HIGH 8.8
See all 24 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences