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Fencer Vulns
high 7.5

CVE-2021-44686 json

calibre before 5.32.0 contains a regular expression that is vulnerable to ReDoS (Regular Expression Denial of Service) in html_preprocess_r…

published 2021-12-06 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-31502

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
5.2%
EPSS 5.2% chance of exploitation in 30 days, percentile 92%
public exploits
0
none known

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.

Patch / fix

  • calibre-ebook calibre 5.32.0
  • calibre Debian 14, Debian 13, Debian 12 5.33.0+dfsg-1

debian advisories DEBIAN-CVE-2021-44686

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-44686 updated cvss 7.5

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

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

5.21% chance of exploitation in the next 30 days, higher than 92% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/dwisiswant0/advisory/issues/18 referenced PoC, tagged "exploit" by a source, unverified
  • bugs.launchpad.net https://bugs.launchpad.net/calibre/+bug/1951979 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.