CVE-2021-44686

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 5.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-12-07 · updated 2026-06-17
Weakness: CWE-400

Description

calibre before 5.32.0 contains a regular expression that is vulnerable to ReDoS (Regular Expression Denial of Service) in html_preprocess_rules in ebooks/conversion/preprocess.py.

Affected products

kovidgoyal calibre: before 5.32.0 — fixed in 5.32.0
Fedoraproject Fedora: 34

How to fix

Upgrade to a fixed version: kovidgoyal calibre 5.32.0. Check the vendor advisory for mitigations.

References

https://bugs.launchpad.net/calibre/+bug/1951979
https://github.com/dwisiswant0/advisory/issues/18
https://github.com/kovidgoyal/calibre/compare/v5.31.1...v5.32.0
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/W7QKFPYJ23KG6WJ5NIYAM4N2NWZCLQGL/
https://bugs.launchpad.net/calibre/+bug/1951979
https://github.com/dwisiswant0/advisory/issues/18
https://github.com/kovidgoyal/calibre/compare/v5.31.1...v5.32.0
https://lists.debian.org/debian-lts-announce/2024/09/msg00005.html
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/W7QKFPYJ23KG6WJ5NIYAM4N2NWZCLQGL/

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