Is CVE-2026-59922 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-59922 being exploited in the wild.

How severe is CVE-2026-59922?

High severity, with a CVSS score of 7.5, published 8 July 2026.

Which products and versions are affected?

mistune (PyPI) < 3.3.0, ECOSYSTEM:introduced=0,fixed=3.3.0.

Is there a fix for CVE-2026-59922?

Yes. mistune (PyPI): upgrade to 3.3.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-59922 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-59922?

Check whether you run mistune (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-59922: lepture Mistune denial of service in formatting plugins

Q: Which products and versions are affected?

mistune (PyPI) < 3.3.0, ECOSYSTEM:introduced=0,fixed=3.3.0.

Q: Is there a fix for CVE-2026-59922?

Yes. mistune (PyPI): upgrade to 3.3.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-59922 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-59922?

Check whether you run mistune (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-59922 · Severity: high · CVSS 7.5 · Published 2026-07-08

Mistune is a Python library used to convert Markdown text into HTML. A vulnerability in its formatting plugins (strikethrough, mark, and insert) allows an attacker to submit specially crafted text that causes the server to consume excessive CPU resources. This can lead to a denial-of-service (DoS) condition where the application becomes unresponsive to legitimate users.

Technologies: mistune (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-59922 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-59922 being exploited in the wild.
How severe is CVE-2026-59922?: High severity, with a CVSS score of 7.5, published 8 July 2026.
Which products and versions are affected?: mistune (PyPI) < 3.3.0, ECOSYSTEM:introduced=0,fixed=3.3.0.
Is there a fix for CVE-2026-59922?: Yes. mistune (PyPI): upgrade to 3.3.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-59922 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-59922?: Check whether you run mistune (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

mistune (PyPI): upgrade to 3.3.0 or later
```
pip install "mistune>=3.3.0"
```

Technical details

The vulnerability is an algorithmic complexity flaw (CWE-407) in `src/mistune/plugins/formatting.py`. When the strikethrough, mark, or insert plugins are enabled, the parser performs a forward scan for matching closing delimiters (`~~`, `==`, or `^^`) for every opening delimiter encountered. In inputs with many repeated markers, this results in O(N²) complexity. An attacker can exploit this by sending a relatively small payload (e.g., 8-16 KB) that exhausts CPU resources. The issue is resolved in version 3.3.0 by implementing a cap on tracked markers or using a more efficient delimiter-stack algorithm.

Affected products

lepture mistune < 3.3.0

Identifiers

CVE-2026-59922
GHSA-c8j7-8cv4-2xmq
PYSEC-2026-2210

Timeline

2026-06-21: disclosed
2026-07-08: advisory: NVD publication
2026-07-20: patched: GitHub Advisory reviewed and updated

References

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