7.5

CVE-2021-44686: calibre-ebook calibre Uncontrolled Resource Consumption

CVSS: 7.5v3.1HighModified
AliasesMGASA-2021-0593UBUNTU-CVE-2021-44686DEBIAN-CVE-2021-44686
Published 06-12-2021Last modified 04-11-2025
Open JSON

Vulnerability summary

CVE-2021-44686 is a high (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in calibre-ebook calibre. EPSS estimates a 5.21% chance of exploitation in the next 30 days, higher than 92.4% of scored vulnerabilities. 2 public exploits are recorded.

Overall risk
41/100
0100
Medium · default modelHow is this calculated?
CVSS score
7.5/10
010
High · v3.1 (NVD)
EPSS score
5.21%
0%100%
Low · +0.23 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits2github, reference

Advisory lineage

Upstream 0 · Downstream 1
DLA-3862-1

Timeline

  1. 06-12-2021
    PublishedVulnerability first disclosed.
  2. 04-11-2025
    Last modifiedVulnerability information updated.

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.

CVSS metrics

4 scores · 3 sources · 2 versions

EPSS trend

Probability

5.21%

Chance of exploitation in the next 30 days

Percentile

92%

Versus all other CVEs

30-day change

+0.23 pp

From 4.99% on 20-09-2026

20-09-202620-10-2026
EPSS score
5.21%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

2 found
  • githubUnverified

    Advisory

    Maturity: poc

  • referenceUnverified

    Exploit Reference (bugs.launchpad.net)

    Maturity: unknown

Weaknesses

CWE · root cause

Affected systems

Calibre-ebook1 product
Debian1 product
  • calibre< 5.33.0+dfsg-1
Fedoraproject1 product
Mageia1 product
  • calibre< 4.23.0-3.1.mga8
Ubuntu1 product
  • calibreAll versions (No fix recorded)

5 vendors · 5 products

References

11 links
Show all 11 references