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

CVE ID :CVE-2026-66033

Published : July 24, 2026, 5:17 p.m. | 32 minutes ago

Description :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.

Severity: 8.7 | HIGH

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