CVE-2026-59923: Mistune is a Python Markdown parser with renderers and plugins

Q: How do I fix CVE-2026-59923?

mistune: upgrade to 3.3.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-59923 being exploited?

CVE-2026-59923 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-59923 affect?

CVE-2026-59923 affects mistune. Severity is medium (CVSS 6.1). Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execut

Q: How urgent is CVE-2026-59923?

Priority 33/100. Public exploit reference

Routine

MEDIUM 6.1UPGRADE

CVE-2026-59923 is a medium-severity flaw (CVSS 6.1) affecting mistune. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execute script in rendered HTML. This issue is fixed in version 3.3.0.

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 72%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-07-08
Last modified	2026-10-25

Publisher (CNA): GitHub, Inc. · Vendor: mistune project

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-08 17:17 UTCPublished CVE record published
2026-10-25 17:10 UTCUpdated Record last modified

mistune project mistune UPGRADE

Affected: < 3.3.0

Fixed in: 3.3.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mistune || rpm -q mistune || mistune --version

2. UPGRADE to 3.3.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mistune

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mistune

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-59923?

mistune: upgrade to 3.3.0. Exact commands for each OS are on this page.

Is CVE-2026-59923 being exploited?

CVE-2026-59923 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-59923 affect?

CVE-2026-59923 affects mistune. Severity is medium (CVSS 6.1). Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execut

How urgent is CVE-2026-59923?

Priority 33/100. Public exploit reference

Software pages

Python vulnerabilities

Related CVEs

CVE-2026-59922 HIGH 7.5 UPGRADE Mistune is a Python Markdown parser with renderers and plugins
CVE-2026-59925 HIGH 7.5 UPGRADE Mistune is a Python Markdown parser with renderers and plugins
CVE-2026-59928 HIGH 7.5 UPGRADE Mistune is a Python Markdown parser with renderers and plugins
CVE-2026-59924 MEDIUM 5.9 UPGRADE Mistune is a Python Markdown parser with renderers and plugins
CVE-2026-59927 MEDIUM 5.3 UPGRADE Mistune is a Python Markdown parser with renderers and plugins

References

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