Vulnerability · Published Feb 27, 2026 · Assigned by GitHub_M
CVE-2026-27824calibre has IP Ban Bypass via X-Forwarded-For Header Spoofing
Medium 5.3
In plain English
A medium-severity security flaw in calibre from kovidgoyal. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | calibre | 6.13.0+repack-2+deb12u6 | DEBIAN-CVE-2026-27824 |
| Debian:13 | calibre | 8.5.0+ds-1+deb13u2 | DEBIAN-CVE-2026-27824 |
| Debian:14 | calibre | 9.4.0+ds+~0.10.5-1 | DEBIAN-CVE-2026-27824 |
| Ubuntu:22.04:LTS | calibre | no fix listed | UBUNTU-CVE-2026-27824 |
| Ubuntu:24.04:LTS | calibre | no fix listed | UBUNTU-CVE-2026-27824 |
| Ubuntu:25.10 | calibre | no fix listed | UBUNTU-CVE-2026-27824 |
| Ubuntu:26.04:LTS | calibre | no fix listed | UBUNTU-CVE-2026-27824 |
| Ubuntu:26.10 | calibre | no fix listed | UBUNTU-CVE-2026-27824 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| kovidgoyal | calibre | < 9.4.0 |
Weakness: CWE-307, CWE-346 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
References
- https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw x_refsource_CONFIRM