Rendering hang via exponential regex backtracking
Published Aug 6, 2026 · Updated Aug 6, 2026
Regular expression denial of service in PyMdown Extensions 11.0 and earlier allows remote attackers to hang Markdown rendering. The caret, tilde, betterem, and magiclink inline processors apply ambiguous regular expressions that exponentially repartition crafted delimiter runs during backtracking. Exploitation requires an application or build worker to render attacker-supplied Markdown and pins the rendering thread at full CPU.
Summary
What happened
Regular expression denial of service in PyMdown Extensions 11.0 and earlier allows remote attackers to hang Markdown rendering. The caret, tilde, betterem, and magiclink inline processors apply ambiguous regular expressions that exponentially repartition crafted delimiter runs during backtracking. Exploitation requires an application or build worker to render attacker-supplied Markdown and pins the rendering thread at full CPU.
The record
- CVE
- CVE-2026-67422
- Published
- Aug 6, 2026
- Updated
- Aug 6, 2026
- Vendor
- facelessuser
- Product
- PyMdown Extensions
- Classifications
- CWE-1333, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 6, 2026CVE publishedPublication date reported by the CVE source.
- Aug 6, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 11.0.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GHSA-gm37-52c6-37mw self-contained ReDoS proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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