CVE-2025-46734: league/commonmark Cross-site Scripting vulnerability in Attributes extension
Description
league/commonmark is a PHP Markdown parser. A 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. 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. 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; and manually-added `href` and `src` attributes now respect the existing `allow_unsafe_links` configuration option. If upgrading is not feasible, please consider disabling the `AttributesExtension` for untrusted users and/or filtering the rendered HTML through a library like HTMLPurifier.
Classification
CVE ID: CVE-2025-46734
CVSS Base Severity: MEDIUM
CVSS Base Score: 6.4
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
Problem Types
CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')Affected Products
Vendor: thephpleague
Product: commonmark
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.01% (probability of being exploited)
EPSS Percentile: 1.72% (scored less or equal to compared to others)
EPSS Date: 2025-06-03 (when was this score calculated)
References
https://nvd.nist.gov/vuln/detail/CVE-2025-46734https://github.com/thephpleague/commonmark/security/advisories/GHSA-3527-qv2q-pfvx
https://github.com/thephpleague/commonmark/commit/f0d626cf05ad3e99e6db26ebcb9091b6cd1cd89b