Vulnerability Description
pymdown-extensions is a collection of extensions for the Python Markdown library. In versions up to and including 11.0, four inline processors (caret, tilde, betterem, and magiclink) use regular expressions whose content groups can partition a run of delimiter characters in exponentially many ways, causing catastrophic backtracking. As a result, a single untrusted Markdown line under 50 bytes rendered with markdown.markdown() in each extension's default configuration drives the rendering thread into unbounded CPU usage that grows exponentially with input length, enabling an unauthenticated remote attacker who can submit Markdown to cause denial of service. The exposure is concrete for web applications that render user-supplied Markdown (comments, wikis, issue bodies, live preview), including any app using pymdownx.extra which bundles the vulnerable betterem default, as well as hosted docs/CI systems that build untrusted Markdown. The issue has been fixed in version 11.0.1.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/facelessuser/pymdown-extensions/commit/c68498598d7b13011bb457
- https://github.com/facelessuser/pymdown-extensions/security/advisories/GHSA-gm37
- https://github.com/facelessuser/pymdown-extensions/security/advisories/GHSA-gm37
FAQ
What is CVE-2026-67422?
CVE-2026-67422 is a vulnerability with a CVSS score of 7.5 (HIGH). pymdown-extensions is a collection of extensions for the Python Markdown library. In versions up to and including 11.0, four inline processors (caret, tilde, betterem, and magiclink) use regular expre...
How severe is CVE-2026-67422?
CVE-2026-67422 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-67422?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.