Bug 2565907 (CVE-2026-121438) - CVE-2026-121438 mistune: mistune: Denial of Service via deeply nested Markdown brackets
Summary: CVE-2026-121438 mistune: mistune: Denial of Service via deeply nested Markdow...
Keywords:
Status: NEW
Alias: CVE-2026-121438
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-11-03 16:01 UTC by OSIDB Bzimport
Modified: 2026-11-05 08:01 UTC (History)
15 users (show)

Fixed In Version:
Clone Of:
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Description OSIDB Bzimport 2026-11-03 16:01:23 UTC 
Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated _contains_nested_link scans that exhaust CPU in parsing applications.
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