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No exploitation reportedFix available

CVE-2021-44686

No exploitation reported by the sources we read.

  • Published2021-12-07
  • Fixed in5.32.0
  • WeaknessCWE-400

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-12-0700:15CVE publishedNVD

Versions per branch

NVD
Calibre-ebook calibre
BranchAffectedFixed in
5.32< 5.32.05.32.0
Fedoraproject fedora
BranchAffectedFixed in
34.x= 34no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • calibreUbuntu:26.04:LTSall versions · no fixed version listed
  • calibreUbuntu:22.04:LTSall versions · no fixed version listed
  • calibreUbuntu:20.04:LTSall versions · no fixed version listed
  • calibreUbuntu:18.04:LTSall versions · no fixed version listed
  • calibreUbuntu:16.04:LTSall versions · no fixed version listed
  • calibreMageia:8all versions · fixed in 4.23.0-3.1.mga8
  • calibreDebian:14all versions · fixed in 5.33.0+dfsg-1
  • calibreDebian:13all versions · fixed in 5.33.0+dfsg-1

2 more package ranges on OSV.dev

Vendor advisories

  • CVE-2021-44686 Red Hat Product Security

    calibre: ReDoS vulnerability in html_preprocess_rules in ebooks/conversion/preprocess.py

Full record on NVD

Fix

  1. Update Calibre-ebook calibre to 5.32.0

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2021-12-07
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-m6m7-mf2p-99p5

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.

Is CVE-2021-44686 actively exploited?

Active exploitation of CVE-2021-44686 has not been confirmed. Its EPSS score was 5.2% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-44686?

CVE-2021-44686 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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Sources for this record