# CVE-2025-9670: mixmark-io turndown commonmark-rules.js redos

> Remote attackers can cause denial of service in the turndown library via inefficient regular expressions in commonmark-rules.js.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Aug 2025
- **Updated:** 29 Aug 2025
- **Also known as:** DEBIAN-CVE-2025-9670, GHSA-6jxv-35jp-jr5v, UBUNTU-CVE-2025-9670

## What is CVE-2025-9670?

CVE-2025-9670 is a medium-severity denial of service vulnerability in mixmark-io turndown, published on 29 Aug 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A security flaw has been discovered in mixmark-io turndown up to 7.2.1. This affects an unknown function of the file src/commonmark-rules.js. Performing manipulation results in inefficient regular expression complexity. It is possible to initiate the attack remotely. The exploit has been released to the public and may be exploited.

Weakness: CWE-400 (Uncontrolled Resource Consumption), CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2025-9670?


## How do I fix CVE-2025-9670?

Upgrade to a fixed version.

## Is CVE-2025-9670 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-9670 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-9670 and fix it if it is affected.

What it is: CVE-2025-9670 is a medium-severity denial of service vulnerability in mixmark-io turndown, published on 29 Aug 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-9670 exists.

Affected product: mixmark-io turndown. 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-2025-9670/ (Markdown: https://insights.sbomify.com/CVE-2025-9670/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-9670
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-9670
- OSV: https://osv.dev/vulnerability/CVE-2025-9670

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-9670/
Summaries are generated and may contain mistakes; the official description above is the record.