XXE in Libexpat
CVE-2026-115506
libexpat through 2.9.0 contains a denial of service vulnerability because billion laughs protection in accountingDiffTolerated() in xmlparse.c detects entity amplification too late. Attackers can supply a moderately sized XML document with a large DTD and nested entity expansions to consume tens of seconds of CPU per parse.
Published .
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
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/libexpat/libexpat/pull/1433 (issue-tracking, patch)
- github.com/libexpat/libexpat/issues/1160 (issue-tracking)
- github.com/hannob/lololol (exploit)
- github.com/libexpat/libexpat (product)
- www.vulncheck.com/advisories/libexpat-through-2.9.0-denial-of-service-via-billi… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-115506?
- CVE-2026-115506 is a high-severity vulnerability in Libexpat, classified under Improper Restriction of Recursive Entity References in DTDs (XML Entity Expansion). CVSS score: 7.5/10. Published 2026-10-22.
- How severe is CVE-2026-115506?
- High severity. CVSS v3 base score is 7.5 out of 10.