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CVE-2026-66035

CVE-2026-66035 · libssh2 Heap Buffer Overflow via ETM Cipher Negotiation

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

libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.

CVSS 7.7 · High · EPSS 0.5% · Fix available

Published
Updated

Stack: system

Affected products and versions

  • libssh2

    Versions
    • ≥ 0, ≤ 1.11.1: Affected (semver)
    • 42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4: 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:Pro:14.04:LTS

    Versions
    • 1.4.3-1
    • 1.4.3-2
    • 1.4.3-2ubuntu0.1
    • 1.4.3-2ubuntu0.2
    • 1.4.3-2ubuntu0.2+esm1
    • 1.4.3-2ubuntu0.2+esm2
    • 1.4.3-2ubuntu0.2+esm3
    • 1.4.3-2ubuntu0.2+esm4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • libssh2 Ubuntu:Pro:16.04:LTS

    Versions
    • 1.5.0-2
    • 1.5.0-2ubuntu0.1
    • 1.5.0-2ubuntu0.1+esm1
    • 1.5.0-2ubuntu0.1+esm2
    • 1.5.0-2ubuntu0.1+esm3
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • libssh2 Ubuntu:Pro:18.04:LTS

    Versions
    • 1.8.0-1
    • 1.8.0-1ubuntu0.1
    • 1.8.0-1ubuntu0.1+esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • libssh2 Ubuntu:Pro:20.04:LTS

    Versions
    • 1.8.0-2.1build1
    • 1.8.0-2.1ubuntu0.1
    • 1.8.0-2.1ubuntu0.1+esm1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • libssh2 Ubuntu:22.04:LTS

    Versions
    • 1.9.0-3
    • 1.10.0-2
    • 1.10.0-2build1
    • 1.10.0-3
    • 1.10.0-3ubuntu0.1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • 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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