EUVD-2026-221709

fkie_cve-2023-22465

Http4s is a Scala interface for HTTP services. Starting with version 0.1.0 and prior to versions 0.21.34, 0.22.15, 0.23.17, and 1.0.0-M38, the `User-Agent` and `Server` header parsers are susceptible to a fatal error on certain inputs. In http4s, modeled headers are lazily parsed, so this only applies to services that explicitly request these typed headers. Fixes are released in 0.21.34, 0.22.15, 0.23.17, and 1.0.0-M38. As a workaround, use the weakly typed header interface.

GHSA-54w6-vxfh-fw7f — Http4s improperly parses User-Agent and Server headers

Affected: Maven: org.http4s:http4s-core_2.13, Maven: org.http4s:http4s-core_2.10, Maven: org.http4s:http4s-core_2.11, Maven: org.http4s:http4s-core_2.12, Maven: org.http4s:http4s-core

### Impact

The `User-Agent` and `Server` header parsers are susceptible to a fatal error on certain inputs. In http4s, modeled headers are lazily parsed, so this only applies to services that explicitly request these typed headers.

#### v0.21.x

```scala val unsafe: Option[`User-Agent`] = req.headers.get(`User-Agent`) ```

#### v0.22.x, v0.23.x, v1.x

```scala val unsafe: Option[`User-Agent`] = req.headers.get[`User-Agent`] val alsoUnsafe: Option[`Server`] = req.headers.get[Server] ```

### Patches

Fixes are released in 0.21.34, 0.22.15, 0.23.17, and 1.0.0-M38.

### Workarounds

#### Use the weakly typed header interface

##### v0.21.x

```scala val safe: Option[Header] = req.headers.get("User-Agent".ci) // but don't do this val unsafe = header.map(_.parsed) ```

##### v0.22.x, v0.23.x, v1.x

```scala val safe: Option[Header] = req.headers.get(ci"User-Agent") ```

Most recent entries from all

EUVD-2026-221709

fkie_cve-2023-22465

GHSA-54w6-vxfh-fw7f — Http4s improperly parses User-Agent and Server headers

gsd-2023-22465