HTTP Request Smuggling Affecting org.http4s:blaze-http_3 package, versions [,0.23.18)[1.0.0-M1,1.0.0-M42)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JAVA-ORGHTTP4S-19822077
- published15 Sept 2026
- disclosed14 Sept 2026
- creditErle Granger II
Introduced: 14 Sep 2026
NewCVE-2026-73494 (opens in a new tab)How to fix?
Upgrade org.http4s:blaze-http_3 to version 0.23.18, 1.0.0-M42 or higher.
Overview
Affected versions of this package are vulnerable to HTTP Request Smuggling in its HTTP/1.1 wire parser (http/src/main/java/org/http4s/blaze/http/parser/), which carries five independent conformance laxities, notably in Content-Length handling relative to RFC 9110 section 8.6 and RFC 9112. An attacker can bypass front-end ACL and authentication checks, poison the response queue on pooled backend connections, and poison caches, by sending a request whose message boundaries the parser resolves differently from the intermediary in front of it. This requires a lenient or legacy intermediary that forwards the malformed bytes rather than an RFC-strict proxy, and no special server setup, since the default BlazeServerBuilder configuration is exploitable.
Workaround
This vulnerability can be avoided by deploying behind an RFC-strict reverse proxy such as nginx, HAProxy, Envoy, or ALB that rejects or re-serializes malformed requests, so the parser never receives bytes it would frame differently.