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.
Published: 2026-08-06
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-gm37-52c6-37mw pymdown-extensions: exponential-backtracking ReDoS in caret, tilde, betterem, and magiclink inline processors
History

Fri, 07 Aug 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 07 Aug 2026 12:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Important


Fri, 07 Aug 2026 01:15:00 +0000

Type Values Removed Values Added
First Time appeared Facelessuser
Facelessuser pymdown Extensions
Vendors & Products Facelessuser
Facelessuser pymdown Extensions

Thu, 06 Aug 2026 22:15:00 +0000

Type Values Removed Values Added
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.
Title pymdown-extensions: Exponential-backtracking ReDoS in caret, tilde, betterem, and magiclink inline processors
Weaknesses CWE-1333
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


Subscriptions

Facelessuser Pymdown Extensions
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-08-07T17:00:29.808Z

Reserved: 2026-07-29T15:02:20.413Z

Link: CVE-2026-67422

cve-icon Vulnrichment

Updated: 2026-08-07T17:00:23.457Z

cve-icon NVD

No data.

cve-icon Redhat

Severity : Important

Publid Date: 2026-08-06T20:26:31Z

Links: CVE-2026-67422 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-08-07T01:15:05Z

Weaknesses