# CVE-2026-66046

## Summary

- **CVE ID:** CVE-2026-66046
- **Severity:** HIGH
- **CVSS Score:** 8.7 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N)
- **CWE:** CWE-407
- **Published:** Aug 18, 2026
- **Last Modified:** Aug 21, 2026

## Description

Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.

## Affected Products

- libexpat project — libexpat (0)

## References

- [CNA](https://github.com/libexpat/libexpat/pull/1321)
- [CNA](https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.59%
- **EPSS Percentile:** 46.1

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._