CVE-2026-66046

HIGHPre-NVD 7.57.5—
EchelonGraph scoreHIGH confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-08-18. a secondary CVSS source baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 7.5Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
7.5
EG Score
7.5(high)
EG Risk
49(Track)
EG Risk 49/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity75% × 45%
Exploitation1% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
50%
KEV
Not listed

Published

August 18, 2026

Last Modified

August 20, 2026

Advisory Details (2)

Auto-updated Aug 18, 2026
Upstream fix merged — awaiting tagged release. Sources: github_pr.
generic

Expat Denial of Service via storeAtts() Quadratic Complexity | Advisories | VulnCheck

https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity
github_pr

[CVE-2026-66046] lib: Migrate `.isCdata` lookup from a linear loop to a hash table lookup

Fix merged in libexpat/libexpat PR #1321 on 2026-08-18 — awaiting tagged release

https://github.com/libexpat/libexpat/pull/1321

Vendor Advisories for CVE-2026-66046(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 16× in last 7d / 16× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-08-21 04:48 UTCEG score recompute
  2. 2026-08-21 04:48 UTCGHSA enrichment
  3. 2026-08-20 22:56 UTCEPSS rescore
  4. 2026-08-20 16:38 UTCEG score recompute
  5. 2026-08-20 16:38 UTCGHSA enrichment
  6. 2026-08-20 15:46 UTCEG score recompute
  7. 2026-08-20 15:46 UTCGHSA enrichment
  8. 2026-08-20 03:50 UTCEG score recompute
  9. 2026-08-20 03:50 UTCGHSA enrichment
  10. 2026-08-19 17:04 UTCEPSS rescore
  11. 2026-08-19 15:39 UTCGHSA enrichment
  12. 2026-08-19 03:30 UTCEG score recompute
  13. 2026-08-19 03:30 UTCGHSA enrichment
  14. 2026-08-18 15:19 UTCEG score recompute
  15. 2026-08-18 14:22 UTCEG score recompute
  16. 2026-08-18 14:19 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-66046?
CVE-2026-66046 is a high vulnerability published on August 18, 2026. 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…
When was CVE-2026-66046 disclosed?
CVE-2026-66046 was first published in the National Vulnerability Database on August 18, 2026, with the most recent update on August 20, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-66046 actively exploited?
CVE-2026-66046 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 50.4% of all scored CVEs.
What is the CVSS score of CVE-2026-66046?
CVE-2026-66046 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-66046?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-66046, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-66046

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