| Package | Affected versions | Patched versions |
|---|---|---|
| org.http4s:blaze-http_2.13 | ≥ 1.0.0-M1, < 1.0.0-M42< 0.23.18 | 1.0.0-M420.23.18 |
| org.http4s:blaze-http_3 | ≥ 1.0.0-M1, < 1.0.0-M42< 0.23.18 | 1.0.0-M420.23.18 |
| org.http4s:http4s-blaze-server_2.13 | < 0.23.18 | 0.23.18 |
Five independent HTTP/1.1 conformance laxities in blaze's hand-written Java parser (http/src/main/java/org/http4s/blaze/http/parser/) cause request-boundary disagreement with a stricter intermediary. All are reachable from a default BlazeServerBuilder with no non-default configuration.
Actual exploitability depends on the fronting proxy — a boundary disagreement requires a pair of parsers that disagree. Where the proxy forwards the malformed bytes and derives a different message boundary, the consequences are the standard set: front-end ACL/auth bypass, response-queue poisoning on pooled backend connections, and cache poisoning. Risk concentrates on lenient or legacy intermediaries.
Deploy behind an RFC-strict reverse proxy (nginx, HAProxy, Envoy, ALB) that rejects or re-serializes malformed requests at the edge; this neutralizes most of these for deployments that cannot upgrade immediately.
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