CVE-2026-27824

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.

The following products are affected by CVE-2026-27824 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2026-27824.

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