CVE-2026-66033: libssh2 libssh2

libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation

CVSS 8.7 HighEPSS 0.0058 · 47th percentile

Published by the CVE Program (CNA: VulnCheck) at 24 Jul 2026, 16:35 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

Affected products, as the CNA wrote them
Vendor	Product	Versions
libssh2	libssh2 pkg:github/libssh2/libssh2	affected 1.11.1 and earlier semver unaffected a2ed82d40964bbc0d64cd717aa0a5a892117d2e6 git Other versions: affected

Identifiers

CVE-2026-66033

CNA

VulnCheck

Weakness (CWE)

CWE-125 · CWE-191

Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
8.7	High	4.0	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	CNA (VulnCheck)Used for this record
7.5	High	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	CNA (VulnCheck)

CISA KEV Not listed.
EPSS 0.0058, the 47th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

This record came from the full history of the CVE Program, published 24 Jul 2026. New records show when each source confirmed them.

Sources

References from the CNA

github.com/libssh2/libssh2/pull/2401 issue-trackingpatch
github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6 patch
www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation third-party-advisory

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.