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Fencer Vulns
medium 6.1

CVE-2026-59929 json

Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution

published 2026-07-08 4 mo ago modified 2026-10-25 14 d ago also GHSA-qfrw-5rxm-mhh2 , PYSEC-2026-2217 , EUVD-2026-42336

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits
0
none known

Summary

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safe_url filter in src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:, and res: to reach rendered href and src attributes and potentially execute script in affected user agents. This issue is fixed in version 3.3.0.

Patch / fix

  • pypi mistune 3.3.0
  • mistune_project mistune 3.3.0
  • python-mistune SLES for SAP applications 16.0, SLES 16.0 3.1.3-160000.5.1

suse advisories SUSE-SU-2026:22655-1

  • python-mistune openSUSE Leap 16.0 3.1.3-160000.5.1

opensuse advisories openSUSE-SU-2026:21339-1

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-2026-59929 updated cvss 6.1

mistune: Mistune: Cross-site scripting via incomplete URL scheme filtering

  • Red Hat Migration Toolkit for Applications 8 mta/mta-solution-server-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-th06-cpu-torch210-py312-rhel9, rhoai/odh-th06-cpu-torch291-py312-rhel9, rhoai/odh-th06-rocm64-torch291-py312-rhel9, rhoai/odh-th06-cuda130-torch210-py312-rhel9, rhoai/odh-th06-cuda130-torch291-py312-rhel9, rhoai/odh-pipeline-runtime-minimal-cpu-py312-rhel9, +16 more Red Hat Satellite 6 satellite/iop-advisor-engine-rhel9
    affected: workaround, no fix available “Fix deferred”

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
none
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/lepture/mistune/security/advisories/GHSA-qfrw-5rxm-mhh2 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
OSV 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
pypi mistune
<3.3.0
3.3.0

Affected products

  • lepture mistune

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation
  • CWE-184 Incomplete List of Disallowed Inputs

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.