CVE-2021-27921: Pillow Denial of Service by Uncontrolled Resource Consumption

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 3.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-03-03 · updated 2026-06-17
Weakness: CWE-20

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.

Affected products

Fedoraproject Fedora: 32, 33, 34
python-pillow Pillow: before 8.1.1 — fixed in 8.1.1
Pypi Pillow: before 8.1.1; 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 (+71) — fixed in 8.1.1

How to fix

Upgrade to a fixed version: python-pillow Pillow 8.1.1; Pypi Pillow 8.1.1. Check the vendor advisory for mitigations.

References

https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/S7G44Z33J4BNI2DPDROHWGVG2U7ZH5JU/
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/ZTSY25UJU7NJUFHH3HWT575LT4TDFWBZ/
https://pillow.readthedocs.io/en/stable/releasenotes/8.1.2.html
https://security.gentoo.org/glsa/202107-33
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/S7G44Z33J4BNI2DPDROHWGVG2U7ZH5JU/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TQQY6472RX4J2SUJENWDZAWKTJJGP2ML/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZTSY25UJU7NJUFHH3HWT575LT4TDFWBZ/
https://pillow.readthedocs.io/en/stable/releasenotes/8.1.1.html
https://security.gentoo.org/glsa/202107-33

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