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CVE-2026-66033

CVE-2026-66033 · libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation

This page contains facts from public vulnerability sources. Check the original advisory before updating.

libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.

CVSS 8.7 · High · EPSS 0.6% · Fix available

Published
Updated

Stack: system

Affected products and versions

  • libssh2

    Versions
    • ≥ 0, ≤ 1.11.1: Affected (semver)
    • a2ed82d40964bbc0d64cd717aa0a5a892117d2e6: Not affected (git)

    No fix published

  • libssh2 Debian:13

    Versions
    • 1.11.1-1
    • 1.11.1-1+deb13u1
    Affected ranges
    • ECOSYSTEM: < 1.11.1-1+deb13u2

    Update to 1.11.1-1+deb13u2

  • libssh2 Debian:14

    Versions
    • 1.11.1-1
    • 1.11.1-2
    • 1.11.1-3
    • 1.11.1-4
    Affected ranges
    • ECOSYSTEM: < 1.11.1-5

    Update to 1.11.1-5

  • libssh2 Ubuntu:24.04:LTS

    Versions
    • 1.11.0-2
    • 1.11.0-3
    • 1.11.0-4
    • 1.11.0-4.1build1
    • 1.11.0-4.1build2
    • 1.11.0-4.1ubuntu0.24.04.1
    • 1.11.0-4.1ubuntu0.24.04.2
    • 1.11.0-4.1ubuntu0.24.04.3
    Affected ranges
    • ECOSYSTEM: < 1.11.0-4.1ubuntu0.24.04.4

    Update to 1.11.0-4.1ubuntu0.24.04.4

  • libssh2 Ubuntu:26.04:LTS

    Versions
    • 1.11.1-1build1
    • 1.11.1-1build2
    • 1.11.1-1ubuntu0.26.04.1
    • 1.11.1-1ubuntu0.26.04.2
    • 1.11.1-1ubuntu0.26.04.3
    Affected ranges
    • ECOSYSTEM: < 1.11.1-1ubuntu0.26.04.4

    Update to 1.11.1-1ubuntu0.26.04.4

Original sources

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