CVE-2021-41084 | Response Splitting from unsanitized headers in http4s

Exp

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.

Published: 2021-09-21 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-41084 is rated High Exploit Risk (72.9/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.20%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-41084

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-41084

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.45% 1.20% +0.74%
2 2025-11-21 0.42% 0.45% +0.03%
3 2025-11-18 — 0.42% —

Full EPSS history (14 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-41084

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.7 3.1 HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 5.8 [email protected]
4.7 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 1.4 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-41084

GitHub Security Advisory for CVE-2021-41084

GHSA-5vcm-3xc3-w7x3 · Severity: high · Ecosystem: maven — Response Splitting from unsanitized headers

Affected software / configurations for CVE-2021-41084

Vendor Product Version Raw CPE
typelevel http4s < 0.21.29 cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:*
typelevel http4s >= 0.22.0, < 0.22.5 cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:*
typelevel http4s >= 0.23.0, < 0.23.4 cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone1:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone10:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone11:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone12:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone13:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone14:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone15:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone16:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone17:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone18:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone19:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone2:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone20:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone21:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone22:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone23:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone24:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone25:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone26:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone3:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone4:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone5:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone6:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone7:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone8:*:*:*:*:*:*
typelevel http4s 1.0.0 cpe:2.3:a:typelevel:http4s:1.0.0:milestone9:*:*:*:*:*:*

References for CVE-2021-41084

cvelogic Threat Intelligence