commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes

Advisories

commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes

severity: high
date: 9/7/2026
Affecting: commonmark >= 1.5.0, < 2.8.4
CVE: CVE-2026-86433
CWE: CWE-407 Inefficient Algorithmic Complexity
CVSS: 8.7
CVSS V4 Vector: 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
References: GitHub Security Advisory (GHSA-g2gp-3wwq-f4ph)
Credit: GrahamCampbell
Description: commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Attributes extension where AttributesListener::findTargetAndDirection() performs quadratic-time sibling list scanning. Unauthenticated attackers can submit approximately 32 KB of repeated attribute blocks to cause parsing to take over 5 seconds, exhausting server resources.

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