Calibre
CVE-2026-27824
MEDIUM
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
Lifecycle Timeline
3DescriptionGitHub Advisory
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.
AnalysisAI
Calibre Content Server's brute-force protection can be bypassed by manipulating the X-Forwarded-For HTTP header, allowing attackers to circumvent IP-based account lockouts and conduct credential stuffing attacks. Public exploit code exists for this vulnerability, which affects Calibre versions prior to 9.4.0 and poses a significant risk to internet-exposed servers where brute-force protection is the primary authentication defense mechanism. No patch is currently available for affected versions.
Technical ContextAI
This vulnerability (CWE-307: Improper Restriction of Excessive Authentication Attempts) affects Calibre. 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-forc
RemediationAI
Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.
Remote code execution in Calibre 9.2.1 and earlier allows authenticated users to write arbitrary files via a path traver
Calibre versions 9.2.1 and below allow authenticated users to write arbitrary files with any extension to any writable l
Remote code execution in Calibre prior to version 9.2.0 through a path traversal flaw in the CHM reader allows local att
Calibre 9.1.0 and earlier contains a path traversal vulnerability in EPUB conversion that allows malicious EPUB files to
calibre is an e-book manager. [CVSS 7.8 HIGH]
gui2/viewer/bookmarkmanager.py in Calibre 3.18 calls cPickle.load on imported bookmark data, which allows remote attacke
Path traversal in Calibre <= 7.14.0 allow unauthenticated attackers to achieve arbitrary file read. Rated high severity
link_to_local_path in ebooks/conversion/plugins/html_input.py in calibre before 6.19.0 can, by default, add resources ou
calibre before 5.32.0 contains a regular expression that is vulnerable to ReDoS (Regular Expression Denial of Service) i
Unsanitized user-input in Calibre <= 7.15.0 allow users with permissions to perform full-text searches to achieve SQL in
HTTP response header injection in Calibre Content Server prior to version 9.4.0 permits authenticated users to inject ar
Unsanitized user-input in Calibre <= 7.15.0 allow attackers to perform reflected cross-site scripting. Rated medium seve
Same technique Authentication Bypass
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SUSE
Severity: MediumShare
External POC / Exploit Code
Leaving vuln.today