CVE-2026-66046

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-08-18. The CNA's CVSS baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cna:vulncheck, epss, ghsa
Trending — Patch released 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: 0.7%CVSS: 7.5Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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
7.5HIGHmedium confidence
EG Risk
49
EG Risk 49/100CISA SSVC

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%
CISA SSVC: Track at low or medium mission impact; Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.7%
EPSS %ILE
53rd
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

August 18, 2026

Last Modified

October 1, 2026

Advisory Details (2)

Auto-updated Aug 18, 2026
Patch available. 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(5)

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

Patch Availability(5)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntulibexpat1-dev (2.1.0-4ubuntu1.4+esm13) @ trusty2026-10-04ubuntu
redhatexpat-0:2.7.3-1.el10_2.52026-09-30redhat
redhatexpat-0:2.5.0-6.el9_8.52026-09-29redhat
redhatexpat-0:2.5.0-4.el8_102026-09-28redhat
redhatexpat-main-2.8.4-0.1.hum12026-09-08redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(7 across 7 ecosystems)
Alpine:v3.21(1)
PackageVulnerable rangeFix by version rangeDependents
expat—
  • every version up to 2.8.4-r0: fixed in 2.8.4-r0
—
Alpine:v3.22(1)
PackageVulnerable rangeFix by version rangeDependents
expat—
  • every version up to 2.8.4-r0: fixed in 2.8.4-r0
—
Alpine:v3.23(1)
PackageVulnerable rangeFix by version rangeDependents
expat—
  • every version up to 2.8.4-r0: fixed in 2.8.4-r0
—
Alpine:v3.24(1)
PackageVulnerable rangeFix by version rangeDependents
expat—
  • every version up to 2.8.4-r0: fixed in 2.8.4-r0
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
expat2.5.0-1, 2.5.0-1+deb12u1, 2.5.0-1+deb12u2, 2.5.0-1+deb12u3
  • every version up to 2.5.0-1+deb12u4: fixed in 2.5.0-1+deb12u4
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
expat2.7.1-2 ... 2.8.5-2 (17 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
expat2.7.1-2 ... 2.8.3-1~deb13u1 (13 versions)
  • every version up to 2.8.4-1: fixed in 2.8.4-1
—

Weakness Classification(1)

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

Additional Vendor Advisories

(2)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 32× in last 7d / 141× 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.

Showing the most recent 100 of 213 total refreshes for this CVE.

  1. 2026-10-04 23:22 UTCEPSS rescore
  2. 2026-10-04 21:43 UTCVendor advisory
  3. 2026-10-04 21:43 UTCGHSA enrichment
  4. 2026-10-04 05:49 UTCVendor advisory
  5. 2026-10-04 05:49 UTCGHSA enrichment
  6. 2026-10-03 17:40 UTCEG score recompute
  7. 2026-10-03 17:40 UTCVendor advisory
  8. 2026-10-03 17:40 UTCGHSA enrichment
  9. 2026-10-03 14:26 UTCEPSS rescore
  10. 2026-10-02 17:56 UTCEPSS rescore
  11. 2026-10-02 15:55 UTCVendor advisory
  12. 2026-10-02 15:55 UTCGHSA enrichment
  13. 2026-10-02 03:46 UTCEG score recompute
  14. 2026-10-02 03:46 UTCVendor advisory
  15. 2026-10-02 03:46 UTCGHSA enrichment
  16. 2026-10-01 19:50 UTCEPSS rescore
  17. 2026-10-01 15:29 UTCEG score recompute
  18. 2026-10-01 15:29 UTCVendor advisory
  19. 2026-10-01 15:29 UTCGHSA enrichment
  20. 2026-10-01 10:10 UTCVendor advisory
  21. 2026-10-01 10:10 UTCGHSA enrichment
  22. 2026-09-30 22:01 UTCEG score recompute
  23. 2026-09-30 22:01 UTCVendor advisory
  24. 2026-09-30 22:01 UTCGHSA enrichment
  25. 2026-09-30 15:03 UTCEPSS rescore
Show 75 more
  1. 2026-09-30 09:51 UTCEG score recompute
  2. 2026-09-30 09:51 UTCVendor advisory
  3. 2026-09-30 09:51 UTCGHSA enrichment
  4. 2026-09-28 21:56 UTCEG score recompute
  5. 2026-09-28 21:56 UTCVendor advisory
  6. 2026-09-28 21:56 UTCGHSA enrichment
  7. 2026-09-28 13:51 UTCEPSS rescore
  8. 2026-09-28 09:29 UTCVendor advisory
  9. 2026-09-28 09:29 UTCGHSA enrichment
  10. 2026-09-27 21:19 UTCEG score recompute
  11. 2026-09-27 21:19 UTCVendor advisory
  12. 2026-09-27 21:19 UTCGHSA enrichment
  13. 2026-09-27 07:58 UTCEG score recompute
  14. 2026-09-27 07:58 UTCVendor advisory
  15. 2026-09-27 07:58 UTCGHSA enrichment
  16. 2026-09-26 15:59 UTCEPSS rescore
  17. 2026-09-25 01:30 UTCEG score recompute
  18. 2026-09-25 01:30 UTCVendor advisory
  19. 2026-09-25 01:30 UTCGHSA enrichment
  20. 2026-09-24 08:56 UTCVendor advisory
  21. 2026-09-24 08:56 UTCGHSA enrichment
  22. 2026-09-23 20:47 UTCEG score recompute
  23. 2026-09-23 20:47 UTCVendor advisory
  24. 2026-09-23 20:47 UTCGHSA enrichment
  25. 2026-09-23 17:54 UTCEPSS rescore
  26. 2026-09-23 08:37 UTCVendor advisory
  27. 2026-09-23 08:37 UTCGHSA enrichment
  28. 2026-09-22 20:27 UTCEG score recompute
  29. 2026-09-22 20:27 UTCVendor advisory
  30. 2026-09-22 20:27 UTCGHSA enrichment
  31. 2026-09-22 06:32 UTCEG score recompute
  32. 2026-09-22 06:32 UTCVendor advisory
  33. 2026-09-22 06:32 UTCGHSA enrichment
  34. 2026-09-21 18:23 UTCVendor advisory
  35. 2026-09-21 18:23 UTCGHSA enrichment
  36. 2026-09-21 06:05 UTCVendor advisory
  37. 2026-09-21 06:05 UTCGHSA enrichment
  38. 2026-09-20 16:31 UTCVendor advisory
  39. 2026-09-20 16:30 UTCGHSA enrichment
  40. 2026-09-20 04:17 UTCVendor advisory
  41. 2026-09-20 04:16 UTCGHSA enrichment
  42. 2026-09-19 16:07 UTCEG score recompute
  43. 2026-09-19 16:07 UTCVendor advisory
  44. 2026-09-19 16:07 UTCGHSA enrichment
  45. 2026-09-19 03:37 UTCEG score recompute
  46. 2026-09-19 03:37 UTCVendor advisory
  47. 2026-09-19 03:37 UTCGHSA enrichment
  48. 2026-09-18 19:28 UTCEPSS rescore
  49. 2026-09-18 15:27 UTCVendor advisory
  50. 2026-09-18 15:27 UTCGHSA enrichment
  51. 2026-09-18 14:22 UTCEG score recompute
  52. 2026-09-18 14:22 UTCVendor advisory
  53. 2026-09-18 14:22 UTCGHSA enrichment
  54. 2026-09-18 12:31 UTCVendor advisory
  55. 2026-09-18 12:31 UTCGHSA enrichment
  56. 2026-09-18 00:15 UTCEG score recompute
  57. 2026-09-18 00:15 UTCVendor advisory
  58. 2026-09-18 00:15 UTCGHSA enrichment
  59. 2026-09-17 11:10 UTCVendor advisory
  60. 2026-09-17 11:10 UTCGHSA enrichment
  61. 2026-09-16 22:58 UTCEG score recompute
  62. 2026-09-16 22:58 UTCVendor advisory
  63. 2026-09-16 22:58 UTCGHSA enrichment
  64. 2026-09-16 14:08 UTCEPSS rescore
  65. 2026-09-16 10:08 UTCEG score recompute
  66. 2026-09-16 10:08 UTCVendor advisory
  67. 2026-09-16 10:08 UTCGHSA enrichment
  68. 2026-09-16 05:15 UTCEPSS rescore
  69. 2026-09-15 20:05 UTCVendor advisory
  70. 2026-09-15 20:05 UTCGHSA enrichment
  71. 2026-09-15 07:55 UTCEG score recompute
  72. 2026-09-15 07:55 UTCVendor advisory
  73. 2026-09-15 07:55 UTCGHSA enrichment
  74. 2026-09-14 19:45 UTCVendor advisory
  75. 2026-09-14 19:45 UTCGHSA enrichment

Related CVEs(same product + same vendor + same CWE)

Same vendor

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redhat:RHSA-2026:72448 · redhat:RHSA-2026:65568 · ubuntu:USN-8813-1

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 on August 18, 2026, with the most recent update on October 1, 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 0.7% probability of exploitation in the next 30 days (53rd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-66046?
CVE-2026-66046 has a CVSS base score of 7.5 (the CNA's own assessment, by vulncheck; NVD's own analysis pending).
How do I remediate CVE-2026-66046?
A fix for CVE-2026-66046 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-66046 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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