Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.

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 High

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 High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00343.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
lepture mistune unaffected
Version Status Constraints
3.0.0 affected < 3.3.0
3.3.0 unaffected —

No data.

No data.

OpenCVE Enrichment is a feature of OpenCVE that uses AI to automatically link vendors and products to CVEs. Learn more on GitHub.

Vendors Products
Lepture Subscribe
Mistune Subscribe
Mistune Project Subscribe
Mistune Subscribe

Project Subscriptions

Vendors Products
Lepture Subscribe
Mistune Subscribe
Mistune Project Subscribe
Mistune Subscribe
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/security/advisories/GHSA-3q64-rw38-243v cve-icon cve-icon cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2026-115349 cve-icon
https://www.cve.org/CVERecord?id=CVE-2026-115349 cve-icon
https://www.vulncheck.com/advisories/mistune-3.0.0-before-3.3.0-denial-of-service-via-nested-bracket-parsing cve-icon cve-icon cve-icon
History

Fri, 23 Oct 2026 04:30:00 +0000

Type Values Removed Values Added
First Time appeared Lepture
Lepture mistune
Vendors & Products Lepture
Lepture mistune

Fri, 23 Oct 2026 00:45:00 +0000

Type Values Removed Values Added
Description Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.
Title Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing
First Time appeared Mistune Project
Mistune Project mistune
Weaknesses CWE-1333
CWE-606
CPEs cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*
Vendors & Products Mistune Project
Mistune Project mistune
References
Metrics threat_severity

None

 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'}

cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}

threat_severity

Important

Projects

Sign in to view the affected projects.

cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-10-22T19:13:26.171Z

Reserved: 2026-10-22T11:20:02.626Z

Link: CVE-2026-115349

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-10-22T19:17:40.597

Modified: 2026-10-22T19:17:40.723

Link: CVE-2026-115349

cve-icon Redhat

Severity : Important

Publid Date: 2026-10-22T19:13:26Z

Links: CVE-2026-115349 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-23T04:15:18Z

Weaknesses