Skip to main content

Mistune CVE-2026-49851

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

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

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

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 1 pypi packages depend on mistune (1 direct, 0 indirect)

Ecosystem-wide dependent count for version 3.3.0.

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. There is no public exploit identified at time of analysis and the issue is not in CISA KEV, but the trigger is trivial to construct and the GitHub Security Advisory documents the root cause precisely.

Technical ContextAI

Mistune (PyPI package 'mistune', authored by lepture) is a pure-Python Markdown parser widely embedded in documentation tooling, note-taking apps, chat/comment systems, and web frameworks that render user-supplied Markdown to HTML. The vulnerability is an algorithmic-complexity issue (CWE-400, Uncontrolled Resource Consumption) rather than a memory-safety bug: the parse_link_text routine, responsible for matching the text portion of '[...]' link syntax, performs a regex search within a loop over nested/consecutive opening brackets. Because each loop iteration re-scans a large suffix of the input, total work grows quadratically with input length. This is the classic 'superlinear parsing' failure mode where worst-case adversarial input is cheap to produce but expensive to process, distinct from catastrophic-backtracking ReDoS in a single regex.

RemediationAI

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). Consult the advisory at https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p for details. Where immediate upgrade is not possible, apply compensating controls at the application boundary: cap the maximum size of Markdown input accepted from untrusted users (the quadratic cost is driven by length, so a strict byte limit such as a few KB sharply bounds worst-case CPU), enforce a per-request CPU/wall-clock timeout or run rendering in a separate worker process that can be killed, and rate-limit or queue Markdown-rendering endpoints to prevent a single client from saturating cores. As a more targeted filter, reject or pre-collapse inputs containing long runs of consecutive '[' characters. Trade-offs: byte limits may truncate legitimate long documents, timeouts/worker isolation add latency and operational complexity, and bracket-run filtering risks false positives on legitimate content, so prefer the version upgrade as the durable fix.

More in Python

View all
CVE-2025-24016 CRITICAL POC
9.9 Feb 10

Wazuh SIEM platform versions 4.4.0 through 4.9.0 contain an unsafe deserialization vulnerability in the DistributedAPI t
CVE-2025-27520 CRITICAL POC
9.8 Apr 04

BentoML version 1.4.2 and earlier contains an unauthenticated remote code execution vulnerability through insecure deser
CVE-2025-2945 CRITICAL POC
9.9 Apr 03

pgAdmin 4 contains critical remote code execution vulnerabilities in the Query Tool download and Cloud Deployment endpoi
CVE-2013-5093 MEDIUM POC
6.8 Sep 27

The renderLocalView function in render/views.py in graphite-web in Graphite 0.9.5 through 0.9.10 uses the pickle Python

CVE-2025-32375 CRITICAL POC
9.8 Apr 09

BentoML is a Python library for building online serving systems optimized for AI apps and model inference. Rated critica
CVE-2014-0224 HIGH POC
7.4 Jun 05

OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0.1h does not properly restrict processing of ChangeCiph
CVE-2024-21644 HIGH POC
7.5 Jan 08

pyLoad download manager version prior to 0.5.0b3.dev77 exposes the Flask SECRET_KEY through an unauthenticated endpoint.
CVE-2026-33017 CRITICAL POC
9.3 Mar 17

Langflow (a visual LLM pipeline builder) contains a critical unauthenticated code execution vulnerability (CVE-2026-3301
CVE-2017-9462 HIGH POC
8.8 Jun 06

In Mercurial before 4.1.3, "hg serve --stdio" allows remote authenticated users to launch the Python debugger, and conse
CVE-2026-49869 CRITICAL POC
10.0 Jun 26

Unauthenticated remote code execution affects Kestra OSS (the open-source event-driven orchestration platform) prior to

CVE-2026-39987 CRITICAL POC
9.3 Apr 08

Unauthenticated remote code execution in Marimo ≤0.20.4 allows attackers to execute arbitrary system commands via the `/
CVE-2024-21645 MEDIUM POC
5.3 Jan 08

pyLoad is the free and open-source Download Manager written in pure Python. Rated medium severity (CVSS 5.3), this vulne

Same weakness CWE-400 – Uncontrolled Resource Consumption

View all
CVE-2023-44487 HIGH POC
7.5
CVE-2026-45498 HIGH POC
7.5
CVE-2016-8610 HIGH
7.5
CVE-2026-28318 HIGH POC
7.5
CVE-2023-38180 HIGH
7.5
CVE-2025-26673 HIGH
7.5
CVE-2015-7978 HIGH
7.5
CVE-2025-27473 HIGH
7.5

Same technique Denial Of Service

View all
CVE-2015-5119 CRITICAL POC
9.8
CVE-2011-2462 CRITICAL POC
9.8
CVE-2011-0611 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8
CVE-2012-0507 CRITICAL POC
9.8
CVE-2014-1761 HIGH POC
7.8
CVE-2015-5122 CRITICAL POC
9.8
CVE-2011-0609 HIGH POC
7.8

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

Share

CVE-2026-49851 vulnerability details – vuln.today
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy