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.

Project Subscriptions

Vendors Products
Calibre-ebook Subscribe
Calibre Subscribe
Kovidgoyal Subscribe
Calibre Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Wed, 04 Mar 2026 16:45:00 +0000

Type Values Removed Values Added
First Time appeared Calibre-ebook
Calibre-ebook calibre
CPEs cpe:2.3:a:calibre-ebook:calibre:*:*:*:*:*:*:*:*
Vendors & Products Calibre-ebook
Calibre-ebook calibre

Mon, 02 Mar 2026 13:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Mon, 02 Mar 2026 12:15:00 +0000

Type Values Removed Values Added
First Time appeared Kovidgoyal
Kovidgoyal calibre
Vendors & Products Kovidgoyal
Kovidgoyal calibre

Fri, 27 Feb 2026 20:00:00 +0000

Type Values Removed Values Added
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.
Title calibre has IP Ban Bypass via X-Forwarded-For Header Spoofing
Weaknesses CWE-307
CWE-346
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N'}


Projects

Sign in to view the affected projects.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-03-02T12:54:32.182Z

Reserved: 2026-02-24T02:32:39.799Z

Link: CVE-2026-27824

cve-icon Vulnrichment

Updated: 2026-03-02T12:54:28.301Z

cve-icon NVD

Status : Analyzed

Published: 2026-02-27T20:21:39.973

Modified: 2026-03-04T16:39:05.407

Link: CVE-2026-27824

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-03-02T12:05:05Z

Weaknesses