league/commonmark contains a XSS vulnerability in Attributes extension

Exploitation

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

CVSS

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

EPSS

• CVE-2025-46734: 0.38% estimated exploitation activity in the next 30 days; percentile 31.81 (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 Cross-site scripting (XSS) vulnerability in the Attributes extension of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to insert malicious JavaScript calls into HTML. Details The league/commonmark library provides configuration options such as htmlinput: 'strip' and allowunsafelinks: false to mitigate cross-site scripting (XSS) attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is enabled, it introduces a way for users to inject arbitrary HTML attributes into elements via Markdown syntax using curly braces. As a result, even with the secure configuration shown above, an attacker can inject dangerous attributes into applications using this extension via a payload such as: Which results in the following HTML: Which causes the JS to execute immediately on page load. Patches Version 2.7.0 contains three changes to prevent this XSS attack vector: - All attributes starting with on are considered…

Published by the source

5 May 2025, 20:40 UTC

Last modified by the source

28 May 2026, 10:01 UTC

Source last checked

26 Oct 2026, 14:48 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-3527-qv2q-pfvx

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# Patch Next advisory brief: CVE-2025-46734

Advisory: league/commonmark contains a XSS vulnerability in Attributes extension
IDs: CVE-2025-46734, GHSA-3527-qv2q-pfvx
Record: https://patchnext.com/advisories/cve-2025-46734 (revision 1, source checked 26 Oct 2026, 14:48 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: league/commonmark 2.7.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist league/commonmark: affected >= 1.5.0, < 2.7.0; fixed in 2.7.0

## 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://github.com/advisories/GHSA-3527-qv2q-pfvx (GitHub-reviewed advisory GHSA-3527-qv2q-pfvx lists affected ranges: Packagist league/commonmark >=1.5.0 <2.7.0)

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