CVE-2026-66033 | libssh2 through 1.11.1, fixed in commit a2ed82d, contains a … | CVSS 7.5 HIGH

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.

Metadata

CVE ID: CVE-2026-66033
State: PUBLISHED
Assigner: VulnCheck
Reserved: 2026-07-23 20:45 UTC
Published: 2026-07-24 16:35 UTC
Last updated: 2026-07-24 16:35 UTC
Primary CWE: CWE-191
Integer Underflow (Wrap or Wraparound)
Vendor / Product: libssh2 / libssh2
Sources: cve.org · NVD

Severity & Metrics

7.5 HIGH CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products (1)

Vendor	Product	Platform	Versions
libssh2	libssh2	—	0 ≤ 1.11.1, a2ed82d40964bbc0d64cd717aa0a5a892117d2e6

Weakness (CWE)

CWE	Source	Description
CWE-125	cna	Out-of-bounds Read
CWE-191	cna	Integer Underflow (Wrap or Wraparound)

CVSS scores (2)

Score	Severity	Version	Source	Vector
8.7	HIGH	4.0	cna	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5	HIGH	3.1	cna	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References (3)