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GHSA-3527-QV2Q-PFVX

Vulnerability from github – Published: 2025-05-05 20:40 – Updated: 2026-03-20 21:27
VLAI
Summary
league/commonmark contains a XSS vulnerability in Attributes extension
Details

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 html_input: 'strip' and allow_unsafe_links: 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:

![](){onerror=alert(1)}

Which results in the following HTML:

<p><img onerror="alert(1)" src="" alt="" /></p>

Which causes the JS to execute immediately on page load.

Patches

Version 2.7.0 contains three changes to prevent this XSS attack vector:

Workarounds

If upgrading is not feasible, please consider:

Severity
6.4 (Medium)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "league/commonmark"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.5.0"
            },
            {
              "fixed": "2.7.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-46734"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-05-05T20:40:36Z",
    "nvd_published_at": "2025-05-05T20:15:21Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nCross-site scripting (XSS) vulnerability in the [Attributes extension](https://commonmark.thephpleague.com/extensions/attributes/) of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to insert malicious JavaScript calls into HTML.\n\n### Details\n\nThe league/commonmark library provides configuration options such as `html_input: \u0027strip\u0027` and `allow_unsafe_links: 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.\n\nAs 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:\n\n```md\n![](){onerror=alert(1)}\n```\n\nWhich results in the following HTML:\n\n```html\n\u003cp\u003e\u003cimg onerror=\"alert(1)\" src=\"\" alt=\"\" /\u003e\u003c/p\u003e\n```\n\nWhich causes the JS to execute immediately on page load.\n\n### Patches\n\nVersion 2.7.0 contains three changes to prevent this XSS attack vector:\n\n- All attributes starting with `on` are considered unsafe and blocked by default\n- [Support for an explicit allowlist of allowed HTML attributes](https://commonmark.thephpleague.com/2.7/extensions/attributes/#configuration)\n- Manually-added `href` and `src` attributes now respect the existing `allow_unsafe_links` configuration option\n\n### Workarounds\n\nIf upgrading is not feasible, please consider:\n\n- Disabling the `AttributesExtension` for untrusted users\n- [Filtering the rendered HTML through a library like HTMLPurifier](https://commonmark.thephpleague.com/security/#additional-filtering)",
  "id": "GHSA-3527-qv2q-pfvx",
  "modified": "2026-03-20T21:27:09Z",
  "published": "2025-05-05T20:40:36Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/security/advisories/GHSA-3527-qv2q-pfvx"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-46734"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/commit/f0d626cf05ad3e99e6db26ebcb9091b6cd1cd89b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/thephpleague/commonmark"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "league/commonmark contains a XSS vulnerability in Attributes extension"
}



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