EUVD-2026-72392
GHSA-jcmh-chhq-rh2x
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-accessible unauthenticated DoS via CPU exhaustion; AC:L because required extensions are commonly enabled and attack imposes no timing constraint; availability-only impact.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
5DescriptionCVE.org
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.
AnalysisAI
Quadratic CPU exhaustion in league/commonmark 2.0.0-2.8.3 allows unauthenticated remote attackers to deny service by submitting Markdown documents that force many headings onto the same base slug. UniqueSlugNormalizer::normalize() restarts its numeric-suffix search from 1 on every slug collision, producing O(K²) comparisons for K colliding slugs - enabling a small, crafted document to consume seconds of CPU time. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that at least one of three extensions is registered in the target's league/commonmark environment: HeadingPermalinkExtension (direct), FootnoteExtension (via anonymous footnote ^[label] syntax), or TableOfContentsExtension (which implicitly requires HeadingPermalinkExtension). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | CVSS 4.0 scores this 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VA:H), reflecting unauthenticated network exploitation with high availability impact; the vendor's AT:N choice implies they regard the required extension configuration as sufficiently common to warrant no attack-requirement modifier, though an argument for AT:P exists given the extensions are explicitly opt-in. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade league/commonmark to version 2.9.0 or later via Composer (composer require league/commonmark:^2.9); this release removes the quadratic behavior entirely while preserving unique heading anchor IDs and producing identical rendered output, per the GHSA advisory at https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all systems running league/commonmark versions 2.0.0-2.8.3 and determine which expose Markdown rendering to untrusted input (user comments, forum posts, uploaded documents); prioritize internet-facing applications and those processing user-generated content. …
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External POC / Exploit Code
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