CVE-2026-73494: blaze: Multiple HTTP/1.1 request-smuggling primitives in blaze's Java wire

Description

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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

http4s blaze

< 0.23.18affected
>= 1.0.0-M1, < 1.0.0-M42affected

org.http4s blaze-http_2.13

< 0.23.18affected
>= 1.0.0-M1, < 1.0.0-M42affected

org.http4s blaze-http_3

< 0.23.18affected
>= 1.0.0-M1, < 1.0.0-M42affected

org.http4s http4s-blaze-server_2.13

< 0.23.18affected

CVE-2026-73494

blaze: Multiple HTTP/1.1 request-smuggling primitives in blaze's Java wire parser