CVE-2021-41084

Name: CVE-2021-41084
Creator: NVD / NIST
Published: 2021-09-21T18:15:07.427+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.7/10EPSS 1.20%

Last modified Jun 17, 2026

CVE-2021-41084 is a medium-severity vulnerability rated 4.7/10 on the CVSS scale. 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). EPSS estimates a 1.20% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

4.7/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N

EPSS Probability

1.20%

64.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions	Update
Typelevel	Http4s	< 0.21.29	—
Typelevel	Http4s	>= 0.22.0, < 0.22.5	—
Typelevel	Http4s	>= 0.23.0, < 0.23.4	—
Typelevel	Http4s	1.0.0	Milestone1

References

https://github.com/http4s/http4s/commit/d02007db1da4f8f3df2dbf11f1db9ac7afc3f9d8Patch, Third Party Advisory
https://github.com/http4s/http4s/security/advisories/GHSA-5vcm-3xc3-w7x3Exploit, Third Party Advisory
https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#fields.valuesVendor Advisory
https://owasp.org/www-community/attacks/HTTP_Response_SplittingThird Party Advisory
https://github.com/http4s/http4s/commit/d02007db1da4f8f3df2dbf11f1db9ac7afc3f9d8Patch, Third Party Advisory
https://github.com/http4s/http4s/security/advisories/GHSA-5vcm-3xc3-w7x3Exploit, Third Party Advisory
https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#fields.valuesVendor Advisory
https://owasp.org/www-community/attacks/HTTP_Response_SplittingThird Party Advisory

Timeline

Published: Sep 21, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-41084?

How severe is CVE-2021-41084?

CVE-2021-41084 has a CVSS score of 4.7/10 (MEDIUM severity). The EPSS model estimates a 1.20% probability of exploitation in the next 30 days.

How do I fix CVE-2021-41084?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-41084?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST