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EUVD-2026-31501

2026-10-05T08:14:40.832935+00:00

EUVD-2026-31501

fkie_cve-2021-41084

2026-10-05T08:14:40.832967+00:00

http4s is an open source scala interface for HTTP. In affected versions http4s is vulnerable to response-splitting or request-splitting attacks when untrusted user input is used to create any of the following fields: Header names (`Header.name`å), Header values (`Header.value`), Status reason phrases (`Status.reason`), URI paths (`Uri.Path`), URI authority registered names (`URI.RegName`) (through 0.21). This issue has been resolved in versions 0.21.30, 0.22.5, 0.23.4, and 1.0.0-M27 perform the following. As a matter of practice http4s services and client applications should sanitize any user input in the aforementioned fields before returning a request or response to the backend. The carriage return, newline, and null characters are the most threatening.

GHSA-5vcm-3xc3-w7x3 — Response Splitting from unsanitized headers

2026-10-05T08:14:40.833002+00:00

Affected: Maven: org.http4s:http4s-client_2.12, Maven: org.http4s:http4s-client_2.13, Maven: org.http4s:http4s-client_3, Maven: org.http4s:http4s-server_2.10, Maven: org.http4s:http4s-server_2.11, Maven: org.http4s:http4s-server_2.12, Maven: org.http4s:http4s-server_2.13, Maven: org.http4s:http4s-server_2.13.0-M5, Maven: org.http4s:http4s-server_3

### Impact

http4s is vulnerable to response-splitting or request-splitting attacks when untrusted user input is used to create any of the following fields:

* Header names (`Header.name`å * Header values (`Header.value`) * Status reason phrases (`Status.reason`) * URI paths (`Uri.Path`) * URI authority registered names (`URI.RegName`) (through 0.21)

The following backends render invalid carriage return, newline, or null characters in an unsafe fashion.

| | blaze-server | ember-server | blaze-client | ember-client | jetty-client | |:---------------|:-------------|:-------------|:-------------|--------------|--------------| | header names | ⚠ | ⚠ | ⚠ | ⚠ | ⚠ | | header values | ⚠ | ⚠ | ⚠ | ⚠ | | | status reasons | ⚠ | ⚠ | | | | | URI paths | | | ⚠ | ⚠ | | | URI regnames | | | ⚠ < 0.22 | ⚠ < 0.22 | |

For example, given the following service:

```scala import cats.effect._ import org.http4s._ import org.http4s.dsl.io._ import org.http4s.server.blaze.BlazeServerBuilder import scala.concurrent.ExecutionContext.global

object ResponseSplit extends IOApp { override def run(args: List[String]): IO[ExitCode] = BlazeServerBuilder[IO](global) .bindH…

gsd-2021-41084

2026-10-05T08:14:40.833076+00:00

gsd-2021-41084