# league/commonmark: Denial of service via crafted code fences, reference links, and emphasis delimiters

Advisory record · `GHSA-j8pm-gj4c-rq4x`

- **Identifiers:** `GHSA-j8pm-gj4c-rq4x` · `CVE-2026-86430` · `PKSA-9q1p-3s19-bp1q`
- **State:** Confirmed
- **Severity:** CVSS 8.7 High
- **Critical:** No
- **Weakness (CWE):** [CWE-407](https://cwe.mitre.org/data/definitions/407.html) · [CWE-1050](https://cwe.mitre.org/data/definitions/1050.html) · [CWE-1333](https://cwe.mitre.org/data/definitions/1333.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md) · [CWE-1050](https://agentprime.io/advisories/tag/cwe-1050.md)
- **Published:** 1 Sept 2026
- **Updated:** 8 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 1 Sept 2026, 20:17 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `league/commonmark` (Packagist): affected `>=0.6.0, <2.9.1`; fixed in `2.9.1`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 8.7 High, CVSS 4.0: `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`, from CNA (VulnCheck)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0049, the 42nd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:06 UTC: First seen by agentprime
- 31 Oct 2026, 14:06 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-j8pm-gj4c-rq4x)

## Sources

- [GitHub Advisory Database: GHSA-j8pm-gj4c-rq4x](https://github.com/advisories/GHSA-j8pm-gj4c-rq4x)
- [OSV: GHSA-j8pm-gj4c-rq4x](https://osv.dev/vulnerability/GHSA-j8pm-gj4c-rq4x)
- <https://github.com/thephpleague/commonmark/security/advisories/GHSA-j8pm-gj4c-rq4x>
- <https://github.com/thephpleague/commonmark/commit/0768217751fbfaeb8d76762f6944e9af7114295e>
- <https://github.com/thephpleague/commonmark/commit/d9375fadc308a63a02950a68d822417a6e4c33b2>
- <https://github.com/thephpleague/commonmark/commit/e0036ef031fd36ec1c3c82db8743fc928b5271c8>
- <https://github.com/thephpleague/commonmark>
- <https://github.com/thephpleague/commonmark/releases/tag/2.9.1>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-j8pm-gj4c-rq4x>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-j8pm-gj4c-rq4x/>. Everything for agents: <https://agentprime.io/llms.txt>.