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HIGH

CVE-2026-86434

CVSS v3

7.5

HIGH

EPSS Score

—

exploit probability

CISA KEV

No

known exploited

Exploitation

—

SSVC status

Description

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 b

Technical details

CVSS v3 Vector
3.1
Published
2026-09-07
Last Modified
2026-09-07

Frequently asked questions

What is CVE-2026-86434?

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 b

Is CVE-2026-86434 actively exploited?

Active exploitation of CVE-2026-86434 has not been confirmed. The EPSS score is N/A%, indicating the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-86434?

CVE-2026-86434 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string 3.1.

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