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CVE-2026-86434 (GCVE-0-2026-86434)

Vulnerability from cvelistv5 – Published: 2026-09-07 12:53 – Updated: 2026-09-07 12:53
VLAI
Title
commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision
Summary
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.
Severity
8.7 (High)
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
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE
  • CWE-407 - Inefficient Algorithmic Complexity
Assigner
References
Impacted products
Vendor Product Version CPE status
thephpleague commonmark Affected: 2.0.0 , < 2.8.4 (semver)
Unaffected: 2.8.4 (semver)
    cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*
Create a notification for this product.
Date Public
2026-08-03 00:00
Credits
GrahamCampbell
Show details on NVD website
To clipboard 

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  }
}



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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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