CVE-2026-66046
Expat XML parser DoS via quadratic attribute parsing causing CPU exhaustion
Is CVE-2026-66046 being exploited?
Not confirmed. CVE-2026-66046 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 0.59% probability of exploitation in the next 30 days.
How severe is CVE-2026-66046?
CVE-2026-66046 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-2026-66046?
Yes. A fix has been recorded for CVE-2026-66046. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-66046 affect?
CVE-2026-66046 affects Expat <= 2.8.3, libexpat, C/C++ applications embedding Expat, Any app parsing untrusted XML (web services, APIs, message brokers). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-66046?
Upgrade Expat above 2.8.3 or apply vendor patch; validate/block untrusted XML and rate-limit parsers.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote unauthenticated attacker can cause CPU exhaustion/denial of service by sending crafted XML with many non-normalized attributes (O(N^2) processing).
Patch when possible
- affected<= 2.8.3
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.