# CVE-2026-86432: commonmark 2.0.0 before 2.8.4 Denial of Service via XML

> Attackers can cause denial of service in the commonmark PHP library by submitting deeply nested Markdown, leading to excessive memory consumption.

- **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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Sep 2026
- **Updated:** 8 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-86432, GHSA-f58g-hmv8-g97m, UBUNTU-CVE-2026-86432

## What is CVE-2026-86432?

CVE-2026-86432 is a medium-severity denial of service vulnerability in thephpleague commonmark, published on 7 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

commonmark versions from 2.0.0 before 2.8.4 contain a denial of service vulnerability in XmlRenderer that emits depth-proportional indentation for every XML tag. Attackers can provide deeply nested Markdown or AST structures to cause quadratic memory consumption and output amplification, exhausting server resources.

Weakness: CWE-405 (Asymmetric Resource Consumption (Amplification))

## Which versions are affected by CVE-2026-86432?


## How do I fix CVE-2026-86432?

Upgrade to a fixed version.

## Is CVE-2026-86432 being exploited?

There is no known exploitation of CVE-2026-86432 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86432 and fix it if it is affected.

What it is: CVE-2026-86432 is a medium-severity denial of service vulnerability in thephpleague commonmark, published on 7 Sep 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-2026-86432 in the wild and no public exploit code.

Affected product: thephpleague commonmark. 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-2026-86432/ (Markdown: https://insights.sbomify.com/CVE-2026-86432/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86432
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86432
- OSV: https://osv.dev/vulnerability/CVE-2026-86432

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-86432/
Summaries are generated and may contain mistakes; the official description above is the record.