# CVE-2026-59925: inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs

> Attackers can cause denial of service in Mistune by submitting long sequences of emphasis markers, triggering quadratic time complexity in the parser.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Jul 2026
- **Updated:** 8 Jul 2026
- **Also known as:** AZL-92217, DEBIAN-CVE-2026-59925, ECHO-a954-a105-41df, GHSA-4j32-57v6-6g45, PYSEC-2026-2213, UBUNTU-CVE-2026-59925

## What is CVE-2026-59925?

CVE-2026-59925 is a high-severity denial of service vulnerability in lepture mistune, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, long sequences of well-formed double-asterisk or triple-asterisk emphasis pairs around a character cause quadratic work in src/mistune/inline_parser.py because the parser scans forward for matching close markers from every potential opening run, allowing denial of service in default Mistune parsing. This issue is fixed in version 3.3.0.

Weakness: CWE-407 (Inefficient Algorithmic Complexity), CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-59925?

3 open source packages ship an affected version, including mistune. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mistune` | PyPI | All versions | 3.3.0 |
| `mistune` | PyPI | All versions | 3.3.0 |
| `mistune` | PyPI | All versions | 3.3.0 |

Products: Mistune Project Mistune.

## How do I fix CVE-2026-59925?

Upgrade mistune to 3.3.0 or later.

## Is CVE-2026-59925 being exploited?

There is no known exploitation of CVE-2026-59925 in the wild and no public exploit code.

## Other vulnerabilities in lepture mistune

- [CVE-2026-59922](https://insights.sbomify.com/CVE-2026-59922/): Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^^` markers (strikethrough / mark / insert) (high 7.5)
- [CVE-2026-59928](https://insights.sbomify.com/CVE-2026-59928/): Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions (high 7.5)
- [CVE-2026-59923](https://insights.sbomify.com/CVE-2026-59923/): Mistune: XSS via percent-encoded javascript URI bypass in safe_url() (medium 6.1)
- [CVE-2026-59929](https://insights.sbomify.com/CVE-2026-59929/): Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution (medium 6.1)
- [CVE-2026-44708](https://insights.sbomify.com/CVE-2026-44708/): Mistune Math Plugin XSS Escape Bypass (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-59925 and fix it if it is affected.

What it is: CVE-2026-59925 is a high-severity denial of service vulnerability in lepture mistune, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-59925 in the wild and no public exploit code.

Affected packages and fixed versions:
- mistune (PyPI): affected all versions; fixed in 3.3.0
- mistune (PyPI): affected all versions; fixed in 3.3.0
- mistune (PyPI): affected all versions; fixed in 3.3.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-59925/ (Markdown: https://insights.sbomify.com/CVE-2026-59925/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59925
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59925
- OSV: https://osv.dev/vulnerability/CVE-2026-59925

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-59925/
Summaries are generated and may contain mistakes; the official description above is the record.