CVE-2026-59928: Mistune is a Python Markdown parser with renderers and plugins

Q: How do I fix CVE-2026-59928?

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

Q: Is CVE-2026-59928 being exploited?

CVE-2026-59928 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-2026-59928 affect?

CVE-2026-59928 affects mistune. Severity is high (CVSS 7.5). Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links envir

Q: How urgent is CVE-2026-59928?

Priority 49/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-59928 is a high-severity flaw (CVSS 7.5) 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, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links environment dictionary handling, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 49%)
CISA exploited list	No
Weakness	CWE-407, CWE-1333
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-2026-59928?

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

Is CVE-2026-59928 being exploited?

CVE-2026-59928 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-2026-59928 affect?

CVE-2026-59928 affects mistune. Severity is high (CVSS 7.5). Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links envir

How urgent is CVE-2026-59928?

Priority 49/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

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-2026-59924 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
CVE-2026-59923 MEDIUM 6.1 UPGRADE Mistune is a Python Markdown parser with renderers and plugins

References

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