CVE-2026-86434

HIGHPre-NVD 7.57.5—
EchelonGraph scoreHIGH confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-09-07. a secondary CVSS source baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 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: 0%CVSS: 7.5Exploit: None knownExposed: 0

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

league/commonmark versions >= 2.0.0 and < 2.8.4 (patched in 2.9.0) contain a denial of service vulnerability in UniqueSlugNormalizer::normalize(), which restarts its numeric-suffix search from 1 on every slug collision, resulting in O(K^2) time complexity for K headings that collapse to the same base slug. The vulnerable path is reached when HeadingPermalinkExtension, FootnoteExtension, or TableOfContentsExtension is registered. An unauthenticated attacker can force many headings onto a single base slug (e.g., via empty ATX headings, identical heading text, or punctuation-only headings) in a small Markdown document, consuming excessive CPU and denying service.

CVSS v3
7.5
EG Score
7.5(high)
EG Risk
38(Track)
EG Risk 38/100SSVC: 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%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
22%
KEV
Not listed

Published

September 7, 2026

Last Modified

September 8, 2026

Advisory Details (2)

Auto-updated Sep 7, 2026
Patch available. Sources: github.
generic

commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision | Advisories | VulnCheck

https://www.vulncheck.com/advisories/commonmark-2.0.0-through-2.8.3-denial-of-service-via-slug-collision
github Patch Available

Denial of service via colliding heading slugs · Advisory · thephpleague/commonmark · GitHub

https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp

Vendor Advisories for CVE-2026-86434(1)

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

Affected Packages

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFixed inDependents
php-league-commonmark2.10.0-1 ... 2.9.0-1 (23 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
php-league-commonmark2.10.0-1 ... 2.9.0-1 (11 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
php-league-commonmark2.7.0-1 ... 2.8.3-1 (8 versions)2.9.0-1—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 27× in last 7d / 45× 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. 2026-09-18 23:48 UTCEG score recompute
  2. 2026-09-18 23:48 UTCGHSA enrichment
  3. 2026-09-18 19:28 UTCEPSS rescore
  4. 2026-09-18 12:14 UTCGHSA enrichment
  5. 2026-09-18 00:39 UTCEG score recompute
  6. 2026-09-18 00:39 UTCGHSA enrichment
  7. 2026-09-17 19:32 UTCEPSS rescore
  8. 2026-09-17 13:04 UTCGHSA enrichment
  9. 2026-09-17 01:29 UTCEG score recompute
  10. 2026-09-17 01:29 UTCGHSA enrichment
  11. 2026-09-16 14:09 UTCEPSS rescore
  12. 2026-09-16 13:55 UTCEG score recompute
  13. 2026-09-16 13:55 UTCGHSA enrichment
  14. 2026-09-16 05:15 UTCEPSS rescore
  15. 2026-09-16 01:55 UTCGHSA enrichment
  16. 2026-09-15 14:20 UTCEG score recompute
  17. 2026-09-15 14:20 UTCGHSA enrichment
  18. 2026-09-15 03:12 UTCEPSS rescore
  19. 2026-09-15 03:12 UTCEPSS rescore
  20. 2026-09-15 02:45 UTCGHSA enrichment
  21. 2026-09-14 15:10 UTCGHSA enrichment
  22. 2026-09-14 03:35 UTCEG score recompute
  23. 2026-09-14 03:35 UTCGHSA enrichment
  24. 2026-09-13 16:01 UTCGHSA enrichment
  25. 2026-09-13 04:27 UTCGHSA enrichment
Show 20 more
  1. 2026-09-12 16:52 UTCEG score recompute
  2. 2026-09-12 16:52 UTCGHSA enrichment
  3. 2026-09-12 05:17 UTCGHSA enrichment
  4. 2026-09-11 17:42 UTCEG score recompute
  5. 2026-09-11 17:42 UTCGHSA enrichment
  6. 2026-09-11 06:08 UTCGHSA enrichment
  7. 2026-09-10 18:32 UTCEG score recompute
  8. 2026-09-10 18:32 UTCGHSA enrichment
  9. 2026-09-10 06:57 UTCGHSA enrichment
  10. 2026-09-09 19:22 UTCGHSA enrichment
  11. 2026-09-09 07:47 UTCEG score recompute
  12. 2026-09-09 07:47 UTCGHSA enrichment
  13. 2026-09-08 22:01 UTCEPSS rescore
  14. 2026-09-08 20:13 UTCGHSA enrichment
  15. 2026-09-08 12:40 UTCGHSA enrichment
  16. 2026-09-08 01:02 UTCEG score recompute
  17. 2026-09-08 01:02 UTCGHSA enrichment
  18. 2026-09-07 13:28 UTCEG score recompute
  19. 2026-09-07 12:57 UTCEG score recompute
  20. 2026-09-07 12:56 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-86434?
CVE-2026-86434 is a high vulnerability published on September 7, 2026. league/commonmark versions >= 2.0.0 and < 2.8.4 (patched in 2.9.0) contain a denial of service vulnerability in UniqueSlugNormalizer::normalize(), which restarts its numeric-suffix search from 1 on every slug collision, resulting in O(K^2) time complexity for K headings that collapse to the same…
When was CVE-2026-86434 disclosed?
CVE-2026-86434 was first published in the National Vulnerability Database on September 7, 2026, with the most recent update on September 8, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-86434 actively exploited?
CVE-2026-86434 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 78.1% of all scored CVEs.
What is the CVSS score of CVE-2026-86434?
CVE-2026-86434 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-86434?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-86434, 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

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