Out-of-bounds Read in Libexpat
CVE-2026-76641
Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for CVE-2026-66046.
Vulnerability class: Buffer Overflow
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.004 (26.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 26.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
Weakness classification (CWE)
References
- github.com/libexpat/libexpat/pull/1331 (issue-tracking)
- github.com/libexpat/libexpat/commit/98599f6dcc2b460410881fe420f5f55d6bec63bf (patch)
- www.vulncheck.com/advisories/expat-out-of-bounds-read-via-dtdcopy (third-party-advisory)
Frequently asked questions
- What is CVE-2026-76641?
- CVE-2026-76641 is a high-severity vulnerability in Libexpat, classified under Out-of-bounds Read. CVSS score: 7.5/10. Published 2026-08-20.
- How severe is CVE-2026-76641?
- High severity. CVSS v3 base score is 7.5 out of 10.