# CVE-2019-25781: Python-Markdown 3.0 through 3.11.2 Denial of Service via Link Bracket Parsing


- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 29 Oct 2026
- **Updated:** 29 Oct 2026
- **Also known as:** GHSA-4g9h-pv2v-fw83

## What is CVE-2019-25781?

CVE-2019-25781 is a high-severity vulnerability in Python-Markdown Markdown, published on 29 Oct 2026. 

### Official description

Python-Markdown 3.0 through 3.11.2 contains an algorithmic complexity vulnerability in inline link parsing that allows remote attackers to exhaust CPU through unmatched brackets. Attackers can submit short Markdown containing repeated [ or ![ characters, forcing LinkInlineProcessor.getText() and getLink() into quadratic scans that keep workers busy for minutes.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2019-25781?


## How do I fix CVE-2019-25781?

No fix has been published for CVE-2019-25781 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-25781 being exploited?

There is no known exploitation of CVE-2019-25781 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-25781 and fix it if it is affected.

What it is: CVE-2019-25781 is a high-severity vulnerability in Python-Markdown Markdown, published on 29 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2019-25781 in the wild and no public exploit code.

Affected product: Python-Markdown Markdown. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2019-25781/ (Markdown: https://insights.sbomify.com/CVE-2019-25781/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-25781
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-25781
- OSV: https://osv.dev/vulnerability/CVE-2019-25781

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-25781/
Summaries are generated and may contain mistakes; the official description above is the record.