calibre has IP Ban Bypass via X-Forwarded-For Header Spoofing
Summary
calibre has IP Ban Bypass via X-Forwarded-For Header Spoofing
Original description
The description as published by the source.
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: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-27824 calibre
- Ubuntu UBUNTU-CVE-2026-27824 calibre
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov