CVE-2021-44686 Denial of service in n/a
An attacker can cause a denial of service in Calibre via a Regular Expression Denial of Service vulnerability in the ebook conversion module.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-44686?
CVE-2021-44686 is a high-severity denial of service vulnerability in Fedoraproject Fedora, published on 6 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-400
Which versions are affected by CVE-2021-44686?
It affects 2 products.
Products include Calibre-Ebook Calibre, Fedoraproject Fedora.
How do I fix CVE-2021-44686?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2021-44686 being exploited?
There is no known exploitation of CVE-2021-44686 in the wild and no public exploit code.
Other vulnerabilities in Fedoraproject Fedora
- CVE-2011-4124 Command injection in Calibre
- CVE-2011-4125 Privilege escalation in Calibre
- CVE-2026-26064 calibre: Path Traversal Vulnerability Enables Arbitrary File Write and Remote Code Execution
- CVE-2026-26065 calibre: Path Traversal can Lead to Arbitrary File Write and Potential Code Execution
- CVE-2026-25635 calibre has a Path Traversal Leading to Arbitrary File Write and Potential Code Execution
Sources
Also known as DEBIAN-CVE-2021-44686, GHSA-m6m7-mf2p-99p5, MGASA-2021-0593, UBUNTU-CVE-2021-44686.