CVE-2026-27824
mediumpriority · track · 21EPSS 0.002 · 7 %ileEUUSEPSS · scored 2026-10-28
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
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
affected products (2)
Products and version ranges known to be affected.
also known as (2)
Other names and identifiers for this entity.
sources
Which sources assert this record, and when.
references (4)
External citations — patches, advisories, analysis.
- https://github.com/kovidgoyal/calibre/releasesPatchcnnvd
- https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrwcnnvd
- https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrwenisa_euvd
- https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrwExploitVendor Advisorynvd
Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.
Free scan