CVE-2026-118370: libexpat libexpat

libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes

CVSS 8.2 HighEPSS 0.0039 · 33rd percentile

Published by the CVE Program (CNA: VulnCheck) at 28 Oct 2026, 02:03 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
libexpat	libexpat pkg:github/libexpat/libexpat	affected 2.9.0 and earlier semver Other versions: unaffected

Identifiers

CVE-2026-118370

CNA

VulnCheck

Weakness (CWE)

CWE-190

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

CISA KEV Not listed.
EPSS 0.0039, the 33rd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

28 Oct 2026, 02:03 UTC Confirmed by the CVE List
28 Oct 2026, 03:17 UTC Confirmed by NVD

Sources

References from the CNA

github.com/libexpat/libexpat/pull/1450 patchissue-tracking
github.com/libexpat/libexpat/commit/1bac53c4fc460a03cd9860f39501c7979f6750ae patch
github.com/libexpat/libexpat/commit/621cb2c78b253ee023a86bc91d6ddb048481c04c patch
github.com/libexpat/libexpat/blob/a76b1174c1ea52abb639a4c69d52b630a8a106a2/expat/lib/xmlparse.c#L4138-L4140 technical-description
github.com/libexpat/libexpat product
www.vulncheck.com/advisories/libexpat-through-2.9.0-integer-overflow-in-storeatts-via-attindex-and-nprefixes 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.