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Public proof of conceptFix available

CVE-2026-59922

A public proof of concept exists; no exploitation attested.

  • Published2026-07-08
  • Fixed in3.3.0
  • WeaknessCWE-1333 · 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, 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.

Timeline

dates in UTC
  1. 2026-07-0817:17CVE 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-2026-59922?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-59922?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Mistune project 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-2026-59922 Red Hat Product Security24 known affected

    mistune: Mistune: Denial of Service via crafted input

    mta/mta-solution-server-rhel9 as a component of Migration Toolkit for Applications 8 · rhoai/odh-pipeline-runtime-datascience-cpu-py312-rhel9 as a component of Red Hat OpenShift AI (RHOAI) · rhoai/odh-pipeline-runtime-minimal-cpu-py312-rhel9 as a component of Red Hat OpenShift AI (RHOAI) · +21 more

Full record on NVD

Fix

  1. Update Mistune project mistune to 3.3.0
  2. Workaround from the vendor Red Hat Product Security CVE-2026-59922 · 24 productsTo mitigate this vulnerability, disable the `strikethrough`, `mark`, and `insert` plugins if they are not essential for your application's functionality. These plugins are not enabled by default in Mistune. Consult your application's documentation for specific instructions on how to configure or di…
  3. No fix available, says the vendor Red Hat Product Security CVE-2026-59922 · 24 productsFix deferred

Advisories and patches

Detection

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

Sources

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2026-07-08
Last Modified
2026-07-09
NVD status
Analyzed
GitHub Advisory
GHSA-c8j7-8cv4-2xmq

Frequently asked questions

What is CVE-2026-59922?

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.

Is CVE-2026-59922 actively exploited?

A proof-of-concept exploit exists for CVE-2026-59922, but active exploitation has not been confirmed at this time.

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

CVE-2026-59922 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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