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Vulnerability record · CVE-2021-41084 · published 21 September 2021

CVE-2021-41084: Typelevel http4s server-side request forgery (ssrf) vulnerability

Typelevel · Http4s

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.

4.7 CVSS 3.1 Medium EPSS 1.2% · top 32.2% CWE-918 · Server-side request forgery (SSRF)CWE-74 · Injection
4.7CVSS 3.1 base score, v2 4.3
1.2%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
8References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/http4s/http4s/commit/d02007db1da4f8f3df2dbf11f1db9ac7afc3f9d8 PatchThird Party Advisory
https://github.com/http4s/http4s/security/advisories/GHSA-5vcm-3xc3-w7x3 ExploitThird Party Advisory
https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#fields.values Vendor Advisory
https://owasp.org/www-community/attacks/HTTP_Response_Splitting Third Party Advisory
https://github.com/http4s/http4s/commit/d02007db1da4f8f3df2dbf11f1db9ac7afc3f9d8 PatchThird Party Advisory
https://github.com/http4s/http4s/security/advisories/GHSA-5vcm-3xc3-w7x3 ExploitThird Party Advisory
https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#fields.values Vendor Advisory
https://owasp.org/www-community/attacks/HTTP_Response_Splitting Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-41084), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.