PT-2026-64380 · Libssh2 · Libssh2

Vladimirelitokarev · CVE-2026-66033 · Published 2026-07-24 · Updated 2026-07-24

NVD

CVSS v3.1

7.5

High

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Fix

Out of bounds Read

Integer Underflow

Weakness Enumeration

CWE-125

CWE-191

Related Identifiers

CVE-2026-66033

Affected Products

Libssh2

References · 4

• https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6 · Patch
• https://nvd.nist.gov/vuln/detail/CVE-2026-66033 · Security Note
• https://vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation · Note
• https://github.com/libssh2/libssh2/pull/2401 · Note