TI-2021-20212 Aliases CVE-2021-44686 GHSA-m6m7-mf2p-99p5

calibre before 5.32.0 contains a regular expression that is vulnerable to ReDoS (Regular…

MEDIUM 41CWE-400Published 2021-12-06 · Updated 2025-11-04

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · High
Fix status: No fix listed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-400.

Summary

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.

Why it matters now

EPSS 0.05214 92nd percentileScored 2026-11-07

Public exploit Yes 2 exploit referencesTagged by NVD

Fix No fix listed No fixed version in the sources yet

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
—	—	all versions	—	No fix listed	CNA

— Vendor— Affected all versions Fixed in — No fix listed CNA

CPE configurations NVD · 2

CPE	Versions	Role	Vendor
cpe:2.3:a:calibre-ebook:calibre::::::::	before 5.32.0	Vulnerable	Calibre
cpe:2.3:o:fedoraproject:fedora:34:::::::*	34	Vulnerable	Fedoraproject

cpe:2.3:a:calibre-ebook:calibre:*:*:*:*:*:*:*:* Versions before 5.32.0 Vulnerable ·Calibre
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:* Versions 34 Vulnerable ·Fedoraproject

Remediation

No fixed version listed by the sources yet.

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product

Red Hat

Timeline

2026-10-02 Threatist record created from CVE-2021-44686
2026-10-03 Alias added: GHSA-m6m7-mf2p-99p5

References

Exploit 2

Patch 1

https://github.com/kovidgoyal/calibre/compare/v5.31.1...v5.32.0

Advisory 1

FEDORA-2021-e42fadbcc3

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences