Request smuggling via incorrect Transfer-Encoding token parsing
Published Sep 15, 2026 · Updated Sep 15, 2026
Request smuggling in http4s Ember before 0.23.35 and 1.0.0-M47 allows remote attackers to bypass controls via ambiguous HTTP framing. HeaderP.parse decodes header bytes with the platform default charset and uses a case-sensitive substring test instead of parsing an ASCII token. Exploitation requires an intermediary that frames the same traffic differently; server deployments can suffer access-control bypass, cross-user request hijacking, or cache poisoning, while client gateways require a malicious or compromised upstream.
Summary
What happened
Request smuggling in http4s Ember before 0.23.35 and 1.0.0-M47 allows remote attackers to bypass controls via ambiguous HTTP framing. HeaderP.parse decodes header bytes with the platform default charset and uses a case-sensitive substring test instead of parsing an ASCII token. Exploitation requires an intermediary that frames the same traffic differently; server deployments can suffer access-control bypass, cross-user request hijacking, or cache poisoning, while client gateways require a malicious or compromised upstream.
The record
- CVE
- CVE-2026-69205
- 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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