league/commonmark: DisallowedRawHtml bypassed when a disallowed tag name ends the raw-HTML literal

Exploitation

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

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-105829: 0.25% estimated exploitation activity in the next 30 days; percentile 16.41 (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 The DisallowedRawHtml extension does not escape a disallowed tag when the tag name is the last thing in the raw HTML. A Markdown line containing just <script is emitted unchanged, and the next block can supply its attributes. With the shipped GFM defaults this allows stored XSS by anyone who can post Markdown. Details DisallowedRawHtmlRenderer escapes tags with this regex: The trailing character class requires one character after the tag name. The block parser does not: RegexHelper::PARTIALHTMLBLOCKOPEN accepts end of line after a tag name, so <script alone opens an HTML block. Because a rendered HtmlBlock has no trailing newline, the regex has nothing to match and the < passes through. In the browser the newline is still present, so the tag name terminates there and whatever follows becomes attributes. This is the same filter that GHSA-4v6x-c7xx-hw9f fixed in 2.8.1. That fix widened the character class but still requires one character, so this case was not covered.…

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-97jj-33gv-5xf9

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-97jj-33gv-5xf9

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-105829

Advisory: league/commonmark: DisallowedRawHtml bypassed when a disallowed tag name ends the raw-HTML literal
IDs: CVE-2026-105829, GHSA-97jj-33gv-5xf9
Record: https://patchnext.com/advisories/cve-2026-105829 (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: Medium (CVSS 6.1)
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 >= 1.3.0, <= 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-97jj-33gv-5xf9 (OSV record GHSA-97jj-33gv-5xf9 lists affected ranges: Packagist league/commonmark >=1.3.0 <2.10.2 (fixed))
- Verified: https://github.com/advisories/GHSA-97jj-33gv-5xf9 (GitHub-reviewed advisory GHSA-97jj-33gv-5xf9 lists affected ranges: Packagist league/commonmark >=1.3.0 <=2.10.1)

Commands are suggestions: review each one before running it.