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.

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact Low

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact Low

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Affected Vendors & Products

Vendors Products
Mistune Project Subscribe
Mistune Subscribe

No data.

No data.

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Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

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

Tue, 03 Nov 2026 14:45:00 +0000

Type Values Removed Values Added
Description 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.
Title Mistune before 3.3.3 Denial of Service via Balanced Bracket Link Parsing
First Time appeared Mistune Project
Mistune Project mistune
Weaknesses CWE-400
CPEs cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*
Vendors & Products Mistune Project
Mistune Project mistune
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

cvssV4_0

{'score': 6.9, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-11-03T14:28:29.879Z

Reserved: 2026-11-03T12:32:14.752Z

Link: CVE-2026-121438

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-11-03T15:17:35.330

Modified: 2026-11-03T15:17:35.457

Link: CVE-2026-121438

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-11-03T16:45:14Z

Weaknesses