Request smuggling via conflicting body framing headers
Published Sep 15, 2026 · Updated Sep 15, 2026
HTTP request smuggling in http4s Ember before 0.23.35 and 1.0.0-M47 allows remote attackers to bypass intermediary access controls. Ember's shared HTTP/1.1 parser accepts messages containing both Transfer-Encoding and Content-Length, allowing peers to select conflicting body boundaries. Server exploitation requires a keep-alive intermediary that forwards both headers and frames by Content-Length; a malicious upstream can similarly desynchronize an Ember client, enabling cache poisoning or cross-user request joining.
Summary
What happened
HTTP request smuggling in http4s Ember before 0.23.35 and 1.0.0-M47 allows remote attackers to bypass intermediary access controls. Ember's shared HTTP/1.1 parser accepts messages containing both Transfer-Encoding and Content-Length, allowing peers to select conflicting body boundaries. Server exploitation requires a keep-alive intermediary that forwards both headers and frames by Content-Length; a malicious upstream can similarly desynchronize an Ember client, enabling cache poisoning or cross-user request joining.
The record
- CVE
- CVE-2026-69204
- Published
- Sep 15, 2026
- Updated
- Sep 15, 2026
- Vendor
- http4s
- Product
- http4s
- Classifications
- T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 15, 2026CVE publishedPublication date reported by the CVE source.
- Sep 15, 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?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 0.23.35
- Affected versionversion=>= 1.0.0-M1, < 1.0.0-M47
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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