http4s blaze up to 0.23.17/1.0.0-M1-1.0.0-M41 HTTP/1.1 Parser parser BodyAndHeaderParser/Http1ServerParser authorization

Summaryinfo

A vulnerability was found in http4s blaze up to 0.23.17/1.0.0-M1-1.0.0-M41. It has been declared as critical. This impacts the function BodyAndHeaderParser/Http1ServerParser of the file http/src/main/java/org/http4s/blaze/http/parser of the component HTTP1.1 Parser. Executing a manipulation can lead to authorization. The identification of this vulnerability is CVE-2026-73494. The attack may be launched remotely. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in http4s blaze up to 0.23.17/1.0.0-M1-1.0.0-M41 and classified as critical. This vulnerability affects the function BodyAndHeaderParser/Http1ServerParser of the file http/src/main/java/org/http4s/blaze/http/parser of the component HTTP1.1 Parser. The manipulation with an unknown input leads to a authorization vulnerability. The CWE definition for the vulnerability is CWE-639. The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

blaze is a Scala library for building asynchronous pipelines, with a focus on network IO. Prior to 0.23.18 and from 1.0.0-M1 until 1.0.0-M42, five HTTP/1.1 conformance laxities in the hand-written Java parser under http/src/main/java/org/http4s/blaze/http/parser/ can cause blaze to derive a different request boundary than a stricter fronting intermediary. A default BlazeServerBuilder accepts invalid or valueless header field names that violate tchar syntax, obsolete folded field lines (obs-fold), unsupported Transfer-Encoding values, duplicate Content-Length fields, and requests containing both Transfer-Encoding and Content-Length. If a lenient or legacy proxy forwards the malformed bytes but interprets them differently, the disagreement can permit front-end authorization bypass, response-queue poisoning on pooled backend connections, or cache poisoning. Exploitation requires a pair of disagreeing parsers; no non-default blaze configuration is required. The affected checks are enforced in BodyAndHeaderParser and Http1ServerParser. This issue is fixed in versions 0.23.18 and 1.0.0-M42.

The advisory is available at github.com. This vulnerability was named CVE-2026-73494 since 08/12/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit.

Upgrading to version 0.23.18 or 1.0.0-M42 eliminates this vulnerability.

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Productinfo

Vendor

• http4s

Name

• blaze

Version

• 0.23.0
• 0.23.1
• 0.23.2
• 0.23.3
• 0.23.4
• 0.23.5
• 0.23.6
• 0.23.7
• 0.23.8
• 0.23.9
• 0.23.10
• 0.23.11
• 0.23.12
• 0.23.13
• 0.23.14
• 0.23.15
• 0.23.16
• 0.23.17
• 1.0.0-M1-1.0.0-M41

Website

• Product: https://github.com/http4s/blaze/

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