CVE-2021-44686

Name: CVE-2021-44686
Creator: NVD / NIST
Published: 2021-12-07T00:15:08.087+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 4.99%

Last modified Jun 17, 2026

CVE-2021-44686 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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.. EPSS estimates a 4.99% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

4.99%

91.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-400

Affected Software

Vendor	Product	Versions
Calibre-Ebook	Calibre	< 5.32.0
Fedoraproject	Fedora	34

References

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

Timeline

Published: Dec 7, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-44686?

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.

How severe is CVE-2021-44686?

CVE-2021-44686 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 4.99% probability of exploitation in the next 30 days.

How do I fix CVE-2021-44686?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-44686?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST