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Public proof of conceptFix available

CVE-2026-49851

A public proof of concept exists; no exploitation attested.

  • Published2026-06-24
  • Fixed in3.3.0
  • WeaknessCWE-1333 · CWE-400 · CWE-407

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC
  1. 2026-06-2418:17CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-49851?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-49851?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

OSV
mistune
BranchAffectedFixed in
3.3< 3.3.03.3.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2026-49851 Red Hat Product Security39 products fixed · 1 known affected

    Mistune: Mistune: Denial of Service via crafted Markdown input

    rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 as a component of Red Hat OpenShift AI (RHOAI)

  • RHSA-2026:60520 Red Hat Product Security39 products fixed

    Red Hat Security Advisory: RHOAI 3.4.4 - Red Hat OpenShift AI

Full record on NVD

Fix

  1. Update mistune to 3.3.0
  2. Vendor fix Red Hat Product Security RHSA-2026:60520 · 39 productsFor Red Hat OpenShift AI 3.4.4 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
  3. Workaround from the vendor Red Hat Product Security RHSA-2026:60520 · 321 productsMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
  4. No fix available, says the vendor Red Hat Product Security CVE-2026-49851 · 1 productAffected

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionpoc2026-06-25
  • OpenCVESSVC decisionpoc—
  • CNACVSS 4.08.7read 2026-10-23
  • CNACVSS 3.17.5read 2026-10-23
  • CNAweakness (CWE)CWE-1333, CWE-400, CWE-407, CWE-770read 2026-10-23
  • FIRST EPSSEPSS score0.6 %2026-10-23
  • OSVaffected packages—
  • Microsoft MSRCadvisory—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 4.0 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/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
Published
2026-06-24
Last Modified
2026-08-28
NVD status
Deferred
MSRC Title
Mistune: Potential DoS via quadratic-time parsing in parse_link_text

Frequently asked questions

What is CVE-2026-49851?

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.

Is CVE-2026-49851 actively exploited?

A proof-of-concept exploit exists for CVE-2026-49851, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-49851?

CVE-2026-49851 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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