libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation
CVE-2026-66033 is fixed in 6 products on 1 platform, first by libssh2-1t64 1.11.0-4.1ubuntu0.24.04.4, released July 24, 2026. It is not reported as exploited. Patch Radar priority: High.
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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| cargo-c · amzn 2023 | 0.10.21-1.amzn2023.0.1 | ALAS2023-2026-2064 | Aug 17, 2026 |
| cargo-c-debuginfo · amzn 2023 | 0.10.21-1.amzn2023.0.1 | ALAS2023-2026-2064 | Aug 17, 2026 |
| libssh2 · Debian 13.5 (trixie) | 1.11.1-1+deb13u2 | DEBIAN-CVE-2026-66033 | Aug 1, 2026 |
| libssh2 · Debian 14 | 1.11.1-5 | DEBIAN-CVE-2026-66033 | Aug 1, 2026 |
| libssh2-1t64 · Ubuntu 24.04.5 LTS (noble) | 1.11.0-4.1ubuntu0.24.04.4 | libssh2-1t64 1.11.0-4.1ubuntu0.24.04.4 | Jul 24, 2026 |
| libssh2-1t64 · Ubuntu 26.04.1 LTS (resolute) | 1.11.1-1ubuntu0.26.04.4 | libssh2-1t64 1.11.1-1ubuntu0.26.04.4 | Jul 24, 2026 |
| libssh2_org · opensuse-leap 16.0 | 1.11.1-160000.5.1 | OPENSUSE-SU-2026:21549-1 | Aug 10, 2026 |
| libssh2_org · sles 15.6 | 1.11.0-150600.20.6.1 | SUSE-SU-2026:3541-1 | Aug 10, 2026 |
| libssh2_org · sles 15.7 | 1.11.0-150600.20.6.1 | SUSE-SU-2026:3541-1 | Aug 10, 2026 |
| libssh2_org · sles 16.0 | 1.11.1-160000.5.1 | SUSE-SU-2026:23225-1 | Aug 10, 2026 |
| rust-cargo-c-debugsource · amzn 2023 | 0.10.21-1.amzn2023.0.1 | ALAS2023-2026-2064 | Aug 17, 2026 |
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