CVE-2021-44686

HIGHNVD 7.57.5—

7.5

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.

CVSS v3: 7.5
EG Score: 7.5(medium)
EPSS: 61.8%
KEV: Not listed

Published

December 7, 2021

Last Modified

November 4, 2025

References (9)

cve@mitrehttps://bugs.launchpad.net/calibre/+bug/1951979
cve@mitrehttps://github.com/dwisiswant0/advisory/issues/18
cve@mitrehttps://github.com/kovidgoyal/calibre/compare/v5.31.1...v5.32.0
cve@mitrehttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/W7QKFPYJ23KG6WJ5NIYAM4N2NWZCLQGL/
af854a3a-2127-422b-91ae-364da2661108https://bugs.launchpad.net/calibre/+bug/1951979
af854a3a-2127-422b-91ae-364da2661108https://github.com/dwisiswant0/advisory/issues/18
af854a3a-2127-422b-91ae-364da2661108https://github.com/kovidgoyal/calibre/compare/v5.31.1...v5.32.0
af854a3a-2127-422b-91ae-364da2661108https://lists.debian.org/debian-lts-announce/2024/09/msg00005.html
af854a3a-2127-422b-91ae-364da2661108https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/W7QKFPYJ23KG6WJ5NIYAM4N2NWZCLQGL/

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 20× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-06-02 20:11 UTCepss_batch
2026-06-02 20:11 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-05-31 22:29 UTCepss_batch
2026-05-31 22:29 UTCepss_batch
2026-05-31 00:15 UTCepss_batch
2026-05-31 00:15 UTCepss_batch
2026-05-29 13:42 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-26 13:42 UTCepss_batch
2026-05-26 13:42 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 06:51 UTCEG score recompute
2026-05-26 06:51 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2021-44686?

CVE-2021-44686 is a high vulnerability published on December 7, 2021. calibre before 5.32.0 contains a regular expression that is vulnerable to ReDoS (Regular Expression Denial of Service) in htmlpreprocessrules in ebooks/conversion/preprocess.py.

When was CVE-2021-44686 disclosed?

CVE-2021-44686 was first published in the National Vulnerability Database on December 7, 2021, with the most recent update on November 4, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-44686 actively exploited?

CVE-2021-44686 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 61.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

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

CVE-2021-44686 has a CVSS v3 base score of 7.5 (NVD).

How do I remediate CVE-2021-44686?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-44686, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2021-44686

📅 Published

🔄 Last Modified

🔗 References (9)