league/commonmark: Quadratic-time denial of service in the GitHub Flavored Markdown Table extension block-start scan

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-105830: 0.37% estimated exploitation activity in the next 30 days; percentile 30.70 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary league/commonmark's GitHub Flavored Markdown Table extension registers TableStartParser as a block-start parser. While a paragraph is the active block, the core block parser calls TableStartParser::tryStart() on every non-blank line. Its first action fetches the entire growing paragraph buffer via getParagraphContent() and runs strpos($paragraph, '|') across all of it. For a paragraph of M pipe-free lines, line k rescans about k lines of buffer, so total work is 1+2+...+M, which is O(M^2). An unauthenticated user who submits a single large paragraph of pipe-free lines that do not begin with a letter (see Attack Chain) to any service that converts untrusted Markdown with GithubFlavoredMarkdownConverter (or any environment that enables TableExtension) drives seconds to tens of seconds of single-core CPU that grows quadratically with body size, enough to exhaust worker processes and deny service. Root Cause The GFM table detector performs a per-line "quick check" against the…

Published by the source

30 Sep 2026, 15:36 UTC

Last modified by the source

9 Oct 2026, 02:56 UTC

Source last checked

26 Oct 2026, 14:53 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-3q6v-r5mr-hxv8

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-3q6v-r5mr-hxv8

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# Patch Next advisory brief: CVE-2026-105830

Advisory: league/commonmark: Quadratic-time denial of service in the GitHub Flavored Markdown Table extension block-start scan
IDs: CVE-2026-105830, GHSA-3q6v-r5mr-hxv8
Record: https://patchnext.com/advisories/cve-2026-105830 (revision 2, source checked 26 Oct 2026, 14:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: league/commonmark 2.10.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist league/commonmark: affected >= 2.0.0, <= 2.10.1; fixed in 2.10.2

## Suggested inspection (read-only)
- Packagist league/commonmark: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on league/commonmark.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-3q6v-r5mr-hxv8 (OSV record GHSA-3q6v-r5mr-hxv8 lists affected ranges: Packagist league/commonmark >=2.0.0 <2.10.2 (fixed))
- Verified: https://github.com/advisories/GHSA-3q6v-r5mr-hxv8 (GitHub-reviewed advisory GHSA-3q6v-r5mr-hxv8 lists affected ranges: Packagist league/commonmark >=2.0.0 <=2.10.1)

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