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Mistune CVE-2026-49851

| EUVDEUVD-2026-39007 HIGH
Uncontrolled Resource Consumption (CWE-400)
2026-06-24 GitHub_M GHSA-qcq2-496w-v96p
Python Denial Of Service Mistune
8.7
CVSS 4.0 · Vendor: GitHub_M
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Severity by source

Vendor (GitHub_M) PRIMARY
8.7 HIGH
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
7.5 HIGH

Remote, unauthenticated, low-complexity input with no interaction yields AV:N/AC:L/PR:N/UI:N; impact is availability-only (A:H) with no confidentiality or integrity effect and no scope change.

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
SUSE
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

2
Patch available
Jun 24, 2026 - 19:17 EUVD
Analysis Generated
Jun 24, 2026 - 18:15 vuln.today

DescriptionCVE.org

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

Articles & Coverage 1

News 3 New Python Vulnerabilities - 1 Critical, 2 High, 1 With POC Jun 25, 2026

AnalysisAI

Uncontrolled CPU consumption in Mistune, a Python Markdown parser, allows remote unauthenticated attackers to cause denial of service against any application that renders untrusted Markdown through versions prior to 3.3.0. The flaw lives in parse_link_text, which runs a regex search inside a loop and re-scans the remaining input each iteration, yielding roughly O(n²) behavior; a tiny payload of many consecutive '[' characters can pin a CPU core. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Reach Markdown-rendering endpoint
Delivery
Submit small input of many '[' chars
Exploit
Trigger O(n²) re-scan in parse_link_text
Execution
Quadratic CPU consumed per request
Persist
Repeat/parallelize to exhaust cores
Impact
Denial of service for legitimate users
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Vulnerability AssessmentAI

Exploitation The only prerequisite is that the target application passes attacker-controlled Markdown to Mistune's parser (any code path reaching parse_link_text) using a version earlier than 3.3.0; the malicious input is simply Markdown containing many consecutive '[' characters. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 8.7 (High) reflects AV:N/AC:L/AT:N/PR:N/UI:N with availability-only impact (VA:H, VC/VI:N), i.e., a fully remote, unauthenticated, low-complexity attack whose sole consequence is service disruption - no confidentiality or integrity loss. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker submits a comment, chat message, issue body, or API payload containing a short string of many consecutive '[' characters to a web service that renders it with a pre-3.3.0 Mistune. The server spends quadratic CPU time in parse_link_text on that single small request, and by sending a handful of such requests concurrently the attacker exhausts available cores and degrades or halts service for legitimate users. …
Remediation Vendor-released patch: upgrade Mistune to 3.3.0 or later (e.g., pip install --upgrade 'mistune>=3.3.0' and update pinned requirements/lockfiles, then rebuild affected containers/images). … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Identify all internal and third-party applications that depend on Mistune (scan requirements.txt, pip.lock, and dependency trees). …

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Threat intelligence, references, and detailed analysis are available after sign-in.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Package Hub 15 SP7 Affected
SUSE Linux Enterprise Module for Python 3 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected

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CVE-2026-49851 vulnerability details – vuln.today
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