CVE-2025-46734 – league/commonmark

Package

Manager: composer
Name: league/commonmark
Vulnerable Version: >=0 <2.7.0

Severity

Level: Medium

CVSS v3.1: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

EPSS: 0.00021 pctl0.03923

Details

league/commonmark contains a XSS vulnerability in Attributes extension ### Summary Cross-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. ### 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: ```md ![](){onerror=alert(1)} ``` Which results in the following HTML: ```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: - All attributes starting with `on` are considered unsafe and blocked by default - [Support for an explicit allowlist of allowed HTML attributes](https://commonmark.thephpleague.com/2.7/extensions/attributes/#configuration) - Manually-added `href` and `src` attributes now respect the existing `allow_unsafe_links` configuration option ### Workarounds If upgrading is not feasible, please consider: - Disabling the `AttributesExtension` for untrusted users - [Filtering the rendered HTML through a library like HTMLPurifier](https://commonmark.thephpleague.com/security/#additional-filtering)

Metadata

Created: 2025-05-05T20:40:36Z
Modified: 2025-05-05T22:06:59Z
Source: https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/05/GHSA-3527-qv2q-pfvx/GHSA-3527-qv2q-pfvx.json
CWE IDs: ["CWE-79"]
Alternative ID: GHSA-3527-qv2q-pfvx
Finding: F008
Auto approve: 1