CVE-2026-121438

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.

CVSS v3 5.3 MEDIUM

5.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact LOW

Scope UNCHANGED

References

Link	Resource
https://github.com/lepture/mistune/commit/fe02f40faf091f86da9ed62c865f31e11da111d7
https://github.com/lepture/mistune/security/advisories/GHSA-47p6-w2rc-5qf7
https://www.vulncheck.com/advisories/mistune-before-3.3.3-denial-of-service-via-balanced-bracket-link-parsing

Configurations

No configuration.

History

03 Nov 2026, 15:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-11-03 15:17

Updated : 2026-11-03 15:17

NVD link : CVE-2026-121438

Mitre link : CVE-2026-121438

CVE.ORG link : CVE-2026-121438

JSON object : View

Products Affected

No product.

CWE

CWE-400

Uncontrolled Resource Consumption

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