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Vulnerability details: VCID-nj3z-4ya4-bqf7
Vulnerability ID VCID-nj3z-4ya4-bqf7
Aliases CVE-2026-27824
Summary 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.
Status Published
Exploitability 0.5
Weighted Severity 4.8
Risk 2.4
Affected and Fixed Packages Package Details
Weaknesses (2)
CWE-307 Improper Restriction of Excessive Authentication Attempts
CWE-346 Origin Validation Error
System Score Found at
epss 0.0002 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
epss 0.0002 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
epss 0.0002 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
epss 0.0002 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
epss 0.0002 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
epss 0.00027 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
epss 0.00027 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
epss 0.00027 https://api.first.org/data/v1/epss?cve=CVE-2026-27824
cvssv3.1 5.3 https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
ssvc Track https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
Reference id Reference type URL
https://api.first.org/data/v1/epss?cve=CVE-2026-27824
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-27824
GHSA-vhxc-r7v8-2xrw https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N Found at https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:P/A:N/T:P/P:M/B:A/M:M/D:T/2026-03-02T12:54:19Z/ Found at https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
Exploit Prediction Scoring System (EPSS)
Percentile 0.05368
EPSS Score 0.0002
Published At April 2, 2026, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2026-04-01T16:39:27.524955+00:00 Debian Oval Importer Import https://www.debian.org/security/oval/oval-definitions-bullseye.xml.bz2 38.0.0