CVE-2026-27824

Name	CVE-2026-27824
Description	calibre is a cross-platform e-book manager for viewing, converting, editing, and cataloging e-books. Prior to version 9.4.0, the calibre Content Server's brute-force protection mechanism uses a ban key derived from both `remote_addr` and the `X-Forwarded-For` header. Since the `X-Forwarded-For` header is read directly from the HTTP request without any validation or trusted-proxy configuration, an attacker can bypass IP-based bans by simply changing or adding this header, rendering the brute-force protection completely ineffective. This is particularly dangerous for calibre servers exposed to the internet, where brute-force protection is the primary defense against credential stuffing and password guessing attacks. Version 9.4.0 contains a fix for the issue.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
calibre (PTS)	bullseye	5.12.0+dfsg-1+deb11u2	vulnerable
	bullseye (security)	5.12.0+dfsg-1+deb11u3	vulnerable
	bookworm	6.13.0+repack-2+deb12u5	vulnerable
	trixie	8.5.0+ds-1+deb13u1	vulnerable
	forky	8.16.2+ds+~0.10.5-3	vulnerable
	sid	9.4.0+ds+~0.10.5-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
calibre	source	(unstable)	9.4.0+ds+~0.10.5-1

https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw