EUVD-2026-54256
GHSA-gm37-52c6-37mw
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Primary rating from Vendor (github).
CVSS VectorVendor: github
Lifecycle Timeline
4Blast Radius
ecosystem impact- 2 pypi packages depend on pymdown-extensions (2 direct, 0 indirect)
Ecosystem-wide dependent count for version 11.0.1.
DescriptionCVE.org
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.
AnalysisAI
Catastrophic regex backtracking in pymdown-extensions 11.0 and earlier enables unauthenticated remote denial of service via crafted Markdown input under 50 bytes. The betterem, caret, tilde, and magiclink inline processors use ambiguous alternation groups that allow exponentially many partition paths for delimiter runs, causing the Python regex engine to spin without bound. …
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Recommended ActionAI
Within 24 hours: audit your application dependencies to identify any use of pymdown-extensions version 11.0 or earlier, including indirect dependencies through pymdownx.extra. …
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