CVE-2026-66046: Expat Denial of Service via storeAtts() Quadratic Complexity
CSIRTS triage
- What
- The storeAtts() function exhibits quadratic time complexity when parsing certain XML attributes, causing denial of service.
- Who is affected
- All Expat users processing untrusted XML input.
- Urgency
- High severity (CVSS 7.5); not yet exploited but easily triggered by malicious XML.
- Action
- Upgrade Expat to the latest patched version and validate XML input size in upstream applications.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66046
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-660460.68% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 50% of all EPSS-scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-66046 | coverage & exploitation status | NVD · CVE.org |
Same CVEs, other sources
How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.