CVE-2026-27810
Calibre-Ebook Calibre ≤ 9.4.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:NSummary
CVE-2026-27810 is a medium-severity HTTP Request/Response Splitting (CWE-113) vulnerability in Calibre-Ebook Calibre. Its CVSS base score is 6.4 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Content Injection (T1659); ranked at the 11th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) and SI-15 (Information Output Filtering) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-9056
Vulnerability Data
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…
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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(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V3.4.2V4.1.3V1.3.6V4.2.3
Mitigating Controls (NIST 800-53 r5) AI
Input validation stops unneutralized CR/LF characters from being accepted and later emitted in HTTP headers.
Output filtering can neutralize CRLF sequences before they reach HTTP response headers.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require input sanitization and header handling that prevent CRLF injection.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect CRLF injection flaws before deployment.
Secure development lifecycle mandates input validation and output encoding that directly prevents CRLF injection into HTTP headers.
Application security requirements explicitly call for controls against injection flaws including HTTP header manipulation.
Secure architecture principles reduce the likelihood of header-splitting vulnerabilities through proper component isolation.
Secure coding standards require neutralization of CRLF sequences before inclusion in HTTP headers.
Logging of HTTP traffic can record header-splitting attempts, aiding detection and forensics.