What’s Vulnerable › Vulnerabilities

CVE-2021-28676: Potential infinite loop in Pillow

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-06-02 · updated 2026-06-17
• Weakness: CWE-835

Description

An issue was discovered in Pillow before 8.2.0. For FLI data, FliDecode did not properly check that the block advance was non-zero, potentially leading to an infinite loop on load.

Affected products

• Fedoraproject Fedora: 33
• python-pillow Pillow: before 8.2.0 — fixed in 8.2.0
• Pypi Pillow: before 8.2.0; 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 (+73) — fixed in 8.2.0

How to fix

Upgrade to a fixed version: python-pillow Pillow 8.2.0; Pypi Pillow 8.2.0. Check the vendor advisory for mitigations.

References

• https://github.com/python-pillow/Pillow/commit/bb6c11fb889e6c11b0ee122b828132ee763b5856
• https://github.com/python-pillow/Pillow/pull/5377
• https://lists.debian.org/debian-lts-announce/2021/07/msg00018.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MQHA5HAIBOYI3R6HDWCLAGFTIQP767FL/
• https://pillow.readthedocs.io/en/stable/releasenotes/8.2.0.html#cve-2021-28676-fix-fli-dos
• https://security.gentoo.org/glsa/202107-33
• https://github.com/python-pillow/Pillow/commit/bb6c11fb889e6c11b0ee122b828132ee763b5856
• https://github.com/python-pillow/Pillow/pull/5377
• https://lists.debian.org/debian-lts-announce/2021/07/msg00018.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MQHA5HAIBOYI3R6HDWCLAGFTIQP767FL/
• https://pillow.readthedocs.io/en/stable/releasenotes/8.2.0.html#cve-2021-28676-fix-fli-dos
• https://security.gentoo.org/glsa/202107-33

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