facelessuser pymdown-extensions up to 11.0.0 caret/tilde/betterem/magiclink markdown.markdown incorrect regex

Summaryinfo

A vulnerability categorized as problematic has been discovered in facelessuser pymdown-extensions up to 11.0.0. Affected by this vulnerability is the function markdown.markdown of the component caret/tilde/betterem/magiclink. Such manipulation leads to incorrect regex. This vulnerability is referenced as CVE-2026-67422. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in facelessuser pymdown-extensions up to 11.0.0 and classified as problematic. Affected by this issue is the function markdown.markdown of the component caret/tilde/betterem/magiclink. The manipulation with an unknown input leads to a incorrect regex vulnerability. Using CWE to declare the problem leads to CWE-185. The product specifies a regular expression in a way that causes data to be improperly matched or compared. Impacted is availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-67422 since 07/29/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit.

Upgrading to version 11.0.1 eliminates this vulnerability.

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Productinfo

Vendor

• facelessuser

Name

• pymdown-extensions

Version

• 11.0

Website

• Product: https://github.com/facelessuser/pymdown-extensions/

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