# CVE-2026-27824: calibre: calibre is a cross-platform e-book manager for viewing, converting, editing, and cataloging e-books

CVE-2026-27824 is fixed in calibre on 1 platform, first by DEBIAN-CVE-2026-27824, released February 27, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-27824
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Feb 27, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | calibre Debian 12.15 (bookworm) | 6.13.0+repack-2+deb12u6 | [DEBIAN-CVE-2026-27824](https://patchblox.com/security/data/fix/linux/debian-cve-2026-27824.md) | Feb 27, 2026 |
| Linux | calibre Debian 13.5 (trixie) | 8.5.0+ds-1+deb13u2 | [DEBIAN-CVE-2026-27824](https://patchblox.com/security/data/fix/linux/debian-cve-2026-27824.md) | Feb 27, 2026 |
| Linux | calibre Debian 14 | 9.4.0+ds+~0.10.5-1 | [DEBIAN-CVE-2026-27824](https://patchblox.com/security/data/fix/linux/debian-cve-2026-27824.md) | Feb 27, 2026 |

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Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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