CVE-2026-27810: calibre-ebook calibre HTTP Request/Response Splitting

Vulnerability summary

CVE-2026-27810 is a medium (CVSS 6.4) HTTP Request/Response Splitting vulnerability in calibre-ebook calibre. EPSS estimates a 0.33% chance of exploitation in the next 30 days, higher than 24.2% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 27-02-2026
   PublishedVulnerability first disclosed.
2. 02-03-2026
   Last modifiedVulnerability information updated.

Description

calibre is a cross-platform e-book manager for viewing, converting, editing, and cataloging e-books. Prior to version 9.4.0, an HTTP Response Header Injection vulnerability in the calibre Content Server allows any authenticated user to inject arbitrary HTTP headers into server responses via an unsanitized `content_disposition` query parameter in the `/get/` and `/data-files/get/` endpoints. All users running the calibre Content Server with authentication enabled are affected. The vulnerability is exploitable by any authenticated user and can also be triggered by tricking an authenticated victim into clicking a crafted link. Version 9.4.0 contains a fix for the issue.

• CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers.