Http4s improperly parses User-Agent and Server headers
Date: 2023-01
Affected: maven/org.http4s:http4s-core, maven/org.http4s:http4s-core_2.12, maven/org.http4s:http4s-core_2.12
Attack vector: other
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2023-22465
CWE: CWE-20
CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

### 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") ```


Mitigations:

Architectural layers (MAESTRO):