# CVE-2019-16215: Denial of service in n/a

> A logged-in user can cause a denial of service in the Zulip server by sending a crafted message that triggers exponential backtracking in the Markdown parser.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** 18 Sep 2019
- **Updated:** 5 Aug 2024
- **Also known as:** GHSA-mmx6-xv2h-w7x8

## What is CVE-2019-16215?

CVE-2019-16215 is a medium-severity denial of service vulnerability in n/a, published on 18 Sep 2019. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

The Markdown parser in Zulip server before 2.0.5 used a regular expression vulnerable to exponential backtracking. A user who is logged into the server could send a crafted message causing the server to spend an effectively arbitrary amount of CPU time and stall the processing of future messages.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2019-16215?

It affects 1 product.


Products: Zulip Zulip Server.

## How do I fix CVE-2019-16215?

No fix has been published for CVE-2019-16215 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-16215 being exploited?

There is no known exploitation of CVE-2019-16215 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2019-18933](https://insights.sbomify.com/CVE-2019-18933/): Information disclosure in n/a (critical 9.8)
- [CVE-2020-15070](https://insights.sbomify.com/CVE-2020-15070/): Code injection in n/a (high 8.8)
- [CVE-2017-0910](https://insights.sbomify.com/CVE-2017-0910/): Missing authorization in Zulip Server (high 8.8)
- [CVE-2025-31478](https://insights.sbomify.com/CVE-2025-31478/): Zulip Authentication Backend Configuration Bypass (high 8.2)
- [CVE-2023-33186](https://insights.sbomify.com/CVE-2023-33186/): Cross-site scripting vulnerability in Zulip Server development branch via topic tooltip (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-16215 and fix it if it is affected.

What it is: CVE-2019-16215 is a medium-severity denial of service vulnerability in n/a, published on 18 Sep 2019. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2019-16215 in the wild and no public exploit code.

Affected product: n/a. 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-2019-16215/ (Markdown: https://insights.sbomify.com/CVE-2019-16215/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-16215
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-16215
- OSV: https://osv.dev/vulnerability/CVE-2019-16215

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-16215/
Summaries are generated and may contain mistakes; the official description above is the record.