What is CVE-2026-66033?

CVE-2026-66033 is a high-severity vulnerability in Libssh2, classified under Out-of-bounds Read. CVSS score: 7.5/10. Published 2026-07-24.

How severe is CVE-2026-66033?

High severity. CVSS v3 base score is 7.5 out of 10.

Out-of-bounds Read in Libssh2

CVE-2026-66033

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 negoti…

Vulnerability class: Buffer Overflow

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Libssh2 — versions 0, a2ed82d40964bbc0d64cd717aa0a5a892117d2e6

Weakness classification (CWE)

CWE-125 — Out-of-bounds Read
CWE-191 — Integer Underflow

References

disclosure@vulncheck.com (issue-tracking, patch)
disclosure@vulncheck.com (patch)
disclosure@vulncheck.com (third-party-advisory)

Frequently asked questions

What is CVE-2026-66033?: CVE-2026-66033 is a high-severity vulnerability in Libssh2, classified under Out-of-bounds Read. CVSS score: 7.5/10. Published 2026-07-24.
How severe is CVE-2026-66033?: High severity. CVSS v3 base score is 7.5 out of 10.