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Fencer Vulns
high 7.5

CVE-2026-49851 json

Mistune: Potential DoS via quadratic-time parsing in parse_link_text

published 2026-06-24 4 mo ago modified 2026-10-25 14 d ago also EUVD-2026-39007 , GHSA-qcq2-496w-v96p , PYSEC-2026-2652

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi mistune 3.3.0
  • Red Hat Red Hat OpenShift AI 3.4 1787073451, 1787073459, 1787073546, 1787073593, 1787073605, 1787073611, 1787073713, 1787073717, 1787073866, 1787073873, 1787073913, 1787073929, 1787073936, 1787074078, 1787074331, 1787076481, 1787076778, 1787077779
  • python-mistune SLES for SAP applications 16.0, SLES 16.0 3.1.3-160000.4.1

suse advisories SUSE-SU-2026:22495-1

  • python-mistune openSUSE Tumbleweed 3.3.2-1.1
  • python-mistune openSUSE Leap 16.0 3.1.3-160000.4.1

opensuse advisories openSUSE-SU-2026:11180-1openSUSE-SU-2026:21191-1

  • python-mistune Azure Linux 3.0 3.3.0-1

azure linux advisories AZL-91047

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-49851 updated cvss 7.5

Mistune: Mistune: Denial of Service via crafted Markdown input

  • Red Hat OpenShift AI (RHOAI) rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9
    affected: workaround, no fix available
  • Red Hat OpenShift AI 3.4 rhoai/odh-th06-cpu-torch210-py312-rhel9 1787076778, rhoai/odh-th06-rocm64-torch291-py312-rhel9 1787076481, rhoai/odh-th06-cuda130-torch210-py312-rhel9 1787077779, rhoai/odh-pipeline-runtime-minimal-cpu-py312-rhel9 1787073936, rhoai/odh-pipeline-runtime-pytorch-cuda-py312-rhel9 1787073873, rhoai/odh-pipeline-runtime-pytorch-rocm-py312-rhel9 1787073611, +13 more
    fixed: vendor fix RHSA-2026:60520
  • Red Hat Migration Toolkit for Applications 8 mta/mta-solution-server-rhel9
    not affected: vulnerable code not present
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-th06-cpu-torch291-py312-rhel9, rhoai/odh-th06-cuda130-torch291-py312-rhel9
    not affected: component not present
  • Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1787330837, rhoai/rhai-cli-rhel9 1787330837, rhoai/odh-automl-rhel9 1786612415, rhoai/odh-mlflow-rhel9 1787226790, rhoai/odh-autorag-rhel9 1786612637, rhoai/odh-trainer-rhel9 1787089049, +81 more Red Hat OpenShift Container Platform 4 python-mistune Red Hat Satellite 6 satellite/iop-advisor-engine-rhel9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.52% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 8.7 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
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 8.7 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
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi mistune
<3.3.0
3.3.0

Affected products

  • lepture mistune
  • Red Hat Red Hat OpenShift AI 3.4
  • Red Hat Migration Toolkit for Applications 8
  • Red Hat Red Hat OpenShift AI (RHOAI)
  • Red Hat Red Hat OpenShift Container Platform 4
  • Red Hat Red Hat Satellite 6

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-770 Allocation of Resources Without Limits or Throttling
  • CWE-407 Inefficient Algorithmic Complexity
  • CWE-1333 Inefficient Regular Expression Complexity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.