CVE-2021-41084: Typelevel HTTP4S

Medium severity, CVSS 4.7. EPSS: 1.2% chance of exploitation in the next 30 days.

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.

Affected products

• Typelevel HTTP4S: before 0.21.29 (fixed in 0.21.29); from 0.22.0, before 0.22.5 (fixed in 0.22.5); from 0.23.0, before 0.23.4 (fixed in 0.23.4); version 1.0.0 only

Published 2021-09-21. Last modified 2026-06-17.