What is the CVSS score of CVE-2026-59922?

CVE-2026-59922 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. EPSS exploitation probability: 0.3%.

Which versions of Mistune are affected by CVE-2026-59922?

Mistune, a Python Markdown parser used in content processing pipelines, contains a denial-of-service vulnerability affecting applications with strikethrough, mark, or insert plugins enabled.. A patch is available.

How to fix or mitigate CVE-2026-59922?

Within 24 hours: Inventory all production systems and applications using Mistune; document which formatting plugins are active. Within 7 days: Deploy input validation to reject excessive consecutive marker characters (~, =, ^); enforce strict timeout and resource limits on parsing operations; disable strikethrough/mark/insert plugins if not operationally required. Within 30 days: Upgrade to Mistune 3.3.0 or later when released; monitor vendor release notes for patched version availability.

Mistune CVE-2026-59922

EUVD-2026-42329 HIGH

Inefficient Algorithmic Complexity (CWE-407)

2026-07-08 GitHub_M

Python Denial Of Service Mistune

7.5

CVSS 3.1 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

vuln.today AI

7.5 HIGH

Untrusted Markdown is typically reachable remotely without auth (AV:N/PR:N/UI:N) and the payload is trivial to craft (AC:L); availability-only impact yields A:H, C:N, I:N.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Lifecycle Timeline

Patch available

Jul 08, 2026 - 18:02 EUVD

Analysis Generated

Jul 08, 2026 - 16:52 vuln.today

DescriptionCVE.org

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a run of closed tilde, equals-sign, or caret marker pairs around a character causes quadratic work in src/mistune/plugins/formatting.py when the strikethrough, mark, or insert plugin scans for matching markers from each possible start position, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.

Articles & Coverage 1

News 10 New Python Vulnerabilities - 2 Critical, 8 High, 1 With POC Jul 09, 2026

AnalysisAI

Denial of service in Mistune, a Python Markdown parser, affects all versions prior to 3.3.0 when the strikethrough, mark, or insert plugins are enabled. Remote attackers can submit crafted Markdown containing runs of closed tilde (~), equals (=), or caret (^) marker pairs that trigger quadratic-time scanning in the formatting plugin, exhausting CPU and rendering the parsing service unresponsive. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access

Reach Markdown rendering endpoint

Delivery

Craft dense ~~/==/^^ marker-pair run

Exploit

Submit as untrusted Markdown input

Execution

Trigger O(n^2) scan in formatting plugin

Persist

Exhaust CPU core

Impact

Repeat to deny service

Access

Reach Markdown rendering endpoint

Delivery

Craft dense ~~/==/^^ marker-pair run

Exploit

Submit as untrusted Markdown input

Execution

Trigger O(n^2) scan in formatting plugin

Persist

Exhaust CPU core

Impact

Repeat to deny service

Vulnerability AssessmentAI

Exploitation	Exploitation requires that the target application (1) parses attacker-supplied Markdown through Mistune at a version below 3.3.0, and (2) has at least one of the strikethrough (~~), mark (==), or insert (^^) formatting plugins enabled - these plugins contain the vulnerable per-start-position scan. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	The CVSS 3.1 score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) reflects a network-reachable, unauthenticated, low-complexity availability-only impact - consistent with an algorithmic-complexity DoS. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	An attacker submits a comment, wiki edit, or API payload containing a long run of closed tilde/equals/caret marker pairs (e.g., many ~~ or == sequences around characters) to a web application that renders user Markdown with Mistune's strikethrough, mark, or insert plugin enabled. The quadratic scan consumes a full CPU core for that request; repeating the submission across connections exhausts server CPU and denies service to legitimate users. …
Remediation	Vendor-released patch: upgrade Mistune to version 3.3.0 or later, which fixes the quadratic scanning in src/mistune/plugins/formatting.py (fix commit 96d0f57f8fe9eeb06bb4cff521962a27d7c402e7, release https://github.com/lepture/mistune/releases/tag/v3.3.0). … Detailed patch versions, workarounds, and compensating controls in full report.