Out-of-bounds Read Affecting libssh2 package, versions <1.11.1-5


Severity

Recommended
0.0
high
0
10

Snyk's Security Team recommends NVD's CVSS assessment. Learn more

Threat Intelligence

EPSS
0.58% (46th percentile)

Do your applications use this vulnerable package?

In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.

Test your applications
  • Snyk IDSNYK-DEBIANUNSTABLE-LIBSSH2-18300236
  • published25 Jul 2026
  • disclosed24 Jul 2026

Introduced: 24 Jul 2026

CVE-2026-66033  (opens in a new tab)
CWE-125  (opens in a new tab)
CWE-191  (opens in a new tab)

How to fix?

Upgrade Debian:unstable libssh2 to version 1.11.1-5 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream libssh2 package and not the libssh2 package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

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 Base Scores

version 3.1