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CVE-2021-41084

18
FAUCET Score

CVE-2021-41084 is a response-splitting or request-splitting vulnerability affecting http4s, an open-source Scala HTTP interface. It arises when untrusted user input is used in header names/values, status reason phrases, URI paths, or URI authority registered names. The vulnerability has a CVSS score of 4.7 (MEDIUM), indicating a network-based attack with low complexity, requiring user interaction, and potentially leading to low integrity impact. There is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
< 0.21.29CPE matchmatch criteria
cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:*
>= 0.22.0, < 0.22.5CPE matchmatch criteria
cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:*
>= 0.23.0, < 0.23.4CPE matchmatch criteria
cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:*
1.0.0CPE matchmatch criteria
cpe:2.3:a:typelevel:http4s:1.0.0:milestone1:*:*:*:*:*:*
1.0.0CPE matchmatch criteria
cpe:2.3:a:typelevel:http4s:1.0.0:milestone10:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.7HIGH

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
2.2
Impact Score
5.8
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.23%
Probability of exploitation in next 30 days
EPSS Percentile
66.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0123 is in the 79th percentile among its peer group of 26,236 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (18)

github_advisorypatch availablevia nvd_reference
View patch
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_2.12Fixed in: 0.21.29
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_2.12Fixed in: 0.22.5
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_2.12Fixed in: 0.23.4
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_2.13Fixed in: 0.21.29
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_2.13Fixed in: 0.22.5
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_2.13Fixed in: 0.23.4
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_3Fixed in: 0.21.29
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_3Fixed in: 0.22.5
mavenpatch availablevia ghsa
Product: org.http4s:http4s-client_3Fixed in: 0.23.4
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_2.12Fixed in: 0.21.29
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_2.12Fixed in: 0.22.5
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_2.12Fixed in: 0.23.4
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_2.13Fixed in: 0.21.29
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_2.13Fixed in: 0.22.5
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_2.13Fixed in: 0.23.4
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_3Fixed in: 0.22.5
mavenpatch availablevia ghsa
Product: org.http4s:http4s-server_3Fixed in: 0.23.4

Vendor Advisories (1)

mavenGHSA-5vcm-3xc3-w7x3high

Response Splitting from unsanitized headers

Sep 22, 2021

References

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