# CVE-2023-2831: Denial of Service while unescaping a Markdown string

> An attacker can cause a Denial of Service in Mattermost by sending messages with excessive escaped characters, requiring a patch to fix.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 16 Jun 2023
- **Updated:** 6 Dec 2024
- **Also known as:** GHSA-4qcm-px3r-jfr8

## What is CVE-2023-2831?

CVE-2023-2831 is a medium-severity denial of service vulnerability in Mattermost Mattermost, published on 16 Jun 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Mattermost fails to unescape Markdown strings in a memory-efficient way, allowing an attacker to cause a Denial of Service by sending a message containing a large number of escaped characters.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2023-2831?

It affects 1 product.


Products: Mattermost Mattermost.

## How do I fix CVE-2023-2831?

No fix has been published for CVE-2023-2831 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-2831 being exploited?

There is no known exploitation of CVE-2023-2831 in the wild and no public exploit code.

## Other vulnerabilities in Mattermost Mattermost

- [CVE-2019-20851](https://insights.sbomify.com/CVE-2019-20851/): Path traversal in n/a (critical 9.1)
- [CVE-2024-39274](https://insights.sbomify.com/CVE-2024-39274/): Malicious remote can add users to arbitrary teams and channels (high 8.7)
- [CVE-2024-39777](https://insights.sbomify.com/CVE-2024-39777/): Malicious remote can invite itself to an arbitrary local channel (high 8.7)
- [CVE-2024-39830](https://insights.sbomify.com/CVE-2024-39830/): Timing attack during remote cluster token comparison when shared channels are enabled (high 8.1)
- [CVE-2023-3615](https://insights.sbomify.com/CVE-2023-3615/): Lack of server certificate validation in websockets connection (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-2831 and fix it if it is affected.

What it is: CVE-2023-2831 is a medium-severity denial of service vulnerability in Mattermost Mattermost, published on 16 Jun 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-2831 in the wild and no public exploit code.

Affected product: Mattermost Mattermost. 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-2023-2831/ (Markdown: https://insights.sbomify.com/CVE-2023-2831/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-2831
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-2831
- OSV: https://osv.dev/vulnerability/CVE-2023-2831

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-2831/
Summaries are generated and may contain mistakes; the official description above is the record.