Authenticated response splitting via unvalidated query parameter
Published Feb 27, 2026 · Updated Feb 27, 2026
HTTP response splitting in the Kovid Goyal calibre Content Server before 9.4.0 allows remote authenticated users to inject arbitrary response headers. The book_fmt() and data_file() handlers URL-decode content_disposition and insert it unvalidated into Content-Disposition, preserving CRLF as new header lines. Authentication and a stored book or data file are required; a crafted link can use a victim's cookie to enable script execution, session fixation, or cache poisoning.
Summary
What happened
HTTP response splitting in the Kovid Goyal calibre Content Server before 9.4.0 allows remote authenticated users to inject arbitrary response headers. The book_fmt() and data_file() handlers URL-decode content_disposition and insert it unvalidated into Content-Disposition, preserving CRLF as new header lines. Authentication and a stored book or data file are required; a crafted link can use a victim's cookie to enable script execution, session fixation, or cache poisoning.
The record
- CVE
- CVE-2026-27810
- Published
- Feb 27, 2026
- Updated
- Feb 27, 2026
- Vendor
- Kovid Goyal
- Product
- calibre
- Classifications
- CWE-113, CAPEC-34, T1190
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Feb 27, 2026CVE publishedPublication date reported by the CVE source.
- Feb 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=< 9.4.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GHSA-5fpj-fxw7-8grw authenticated response-header injection proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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