Improper Restriction of Excessive Authentication Attempts Affecting calibre package, versions <9.4.0+ds+~0.10.5-1


Severity

Recommended
0.0
medium
0
10

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Threat Intelligence

EPSS
0.15% (5th percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-CALIBRE-15363629
  • published28 Feb 2026
  • disclosed27 Feb 2026

Introduced: 27 Feb 2026

CVE-2026-27824  (opens in a new tab)
CWE-307  (opens in a new tab)
CWE-346  (opens in a new tab)

How to fix?

Upgrade Debian:unstable calibre to version 9.4.0+ds+~0.10.5-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream calibre package and not the calibre package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

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 Base Scores

version 3.1