CVE-2026-55200: libssh2 libssh2

libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c

CVSS 9.2 CriticalCriticalEPSS 0.039 · 90th percentile

Critical, because:

CVSS score 9.2: 9.0 or more.

Published by the CVE Program (CNA: VulnCheck) at 17 Jun 2026, 19:03 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 semver affected 1c3f1b7da588f2652260285529ec3c1f1125eb4e to before 97acf3dfda80c91c3a8c9f2372546301d4a1a7a8 git Other versions: unaffected

Identifiers

CVE-2026-55200

CNA

VulnCheck

Weakness (CWE)

CWE-680

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
9.2	Critical	4.0	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N	CNA (VulnCheck)Used for this record
8.1	High	3.1	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H	CNA (VulnCheck)

CISA KEV Not listed.
EPSS 0.039, the 90th 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 17 Jun 2026. New records show when each source confirmed them.

Sources

References from the CNA

github.com/libssh2/libssh2/pull/2052 issue-tracking
github.com/libssh2/libssh2/commit/97acf3dfda80c91c3a8c9f2372546301d4a1a7a8 patch
www.vulncheck.com/advisories/libssh2-out-of-bounds-write-via-unchecked-packet-length-in-transport-c 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.