libexpat is a widely used XML parsing library embedded in many apps and services; a DoS against it can disrupt multiple services and infrastructure across organizations.
CVE-2026-115506
libexpat XML parser CPU DoS via delayed 'billion laughs' detection.
Is CVE-2026-115506 being exploited?
Not confirmed. CVE-2026-115506 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.46% probability of exploitation in the next 30 days.
How severe is CVE-2026-115506?
CVE-2026-115506 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-115506?
Yes. A fix has been recorded for CVE-2026-115506. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-115506 affect?
CVE-2026-115506 affects libexpat <= 2.9.0, Any application or service using libexpat for XML parsing. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-115506?
Update libexpat to patched release; validate/block DTDs and limit entity expansion.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote attackers can supply crafted XML with nested entity expansions to cause high CPU use per parse, causing denial of service and service degradation.
Patch when possible
- affected<= 2.9.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.