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NVD HIGH: CVE-2026-66033 — libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication i...

·Source: NIST NVD

Updated:

Executive Summary

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

Analysis

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 Score: 7.5. Published: 2026-07-24T17:17:35.263.

Indicators of Compromise (1)

CVE (1)
CVE-2026-66033
NVDMITRE CVE
Source Attribution

Originally published by NIST NVD on Jul 24, 2026. Verified by: NIST.

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