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Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVE-2025-46734

Medium
6.4/10

Summary

The package league/commonmark is a PHP Markdown parser. A Cross-site Scripting (XSS) vulnerability in the "Attributes Extension" of the league/commonmark package versions 1.5.0 through 2.6.2, 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`.

  • LOW
  • NETWORK
  • LOW
  • CHANGED
  • NONE
  • LOW
  • LOW
  • NONE

CWE-79 - Cross Site Scripting

Cross-Site Scripting, commonly referred to as XSS, is the most dominant class of vulnerabilities. It allows an attacker to inject malicious code into a pregnable web application and victimize its users. The exploitation of such a weakness can cause severe issues such as account takeover, and sensitive data exfiltration. Because of the prevalence of XSS vulnerabilities and their high rate of exploitation, it has remained in the OWASP top 10 vulnerabilities for years.

References

Advisory Timeline

  • Published