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.

CVSS v3 5.3 MEDIUM

5.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact NONE

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw	Exploit Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:calibre-ebook:calibre:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-02-27 20:21

Updated : 2026-03-04 16:39

NVD link : CVE-2026-27824

Mitre link : CVE-2026-27824

CVE.ORG link : CVE-2026-27824

JSON object : View

Products Affected

calibre-ebook

calibre

CWE

CWE-307

Improper Restriction of Excessive Authentication Attempts

CWE-346

Origin Validation Error

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