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Fencer Intel
high 8.7

CVE-2021-41084 json

Response Splitting from unsanitized headers in http4s

published 5y ago modified 4mo ago also GHSA-5vcm-3xc3-w7x3 , EUVD-2021-1987

cvss
8.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 69%
public exploits
0
none known

Summary

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.

Patch / fix

  • maven org.http4s:http4s-client_2.12 0.21.29, 0.22.5, 0.23.4
  • maven org.http4s:http4s-client_2.13 0.21.29, 0.22.5, 0.23.4
  • maven org.http4s:http4s-client_3 0.21.29, 0.22.5, 0.23.4
  • maven org.http4s:http4s-server_2.12 0.21.29, 0.22.5, 0.23.4
  • maven org.http4s:http4s-server_2.13 0.21.29, 0.22.5, 0.23.4
  • maven org.http4s:http4s-server_3 0.22.5, 0.23.4
  • typelevel http4s 0.21.29, 0.22.5, 0.23.4

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Exploit prediction

1.24% chance of exploitation in the next 30 days, higher than 69% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/http4s/http4s/security/advisories/GHSA-5vcm-3xc3-w7x3 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 8.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
NVD 3.1 4.7 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N
GitHub 3.1 8.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
maven org.http4s:http4s-client_2.12
<0.21.29
>=0.22.0, <0.22.5
>=0.23.0, <0.23.4
0.21.29
0.22.5
0.23.4
maven org.http4s:http4s-client_2.13
<0.21.29
>=0.22.0, <0.22.5
>=0.23.0, <0.23.4
0.21.29
0.22.5
0.23.4
maven org.http4s:http4s-client_3
<0.21.29
>=0.22.0, <0.22.5
>=0.23.0, <0.23.4
0.21.29
0.22.5
0.23.4
maven org.http4s:http4s-server_2.10
<=0.21.28
 no fix listed
maven org.http4s:http4s-server_2.11
<=0.21.28
 no fix listed
maven org.http4s:http4s-server_2.12
<0.21.29
>=0.22.0, <0.22.5
>=0.23.0, <0.23.4
0.21.29
0.22.5
0.23.4
maven org.http4s:http4s-server_2.13
<0.21.29
>=0.22.0, <0.22.5
>=0.23.0, <0.23.4
0.21.29
0.22.5
0.23.4
maven org.http4s:http4s-server_2.13.0-M5
<=0.21.28
 no fix listed
maven org.http4s:http4s-server_3
>=0.22.0, <0.22.5
>=0.23.0, <0.23.4
0.22.5
0.23.4

Affected products

  • http4s http4s

Classification

Weakness
  • CWE-918 Server-Side Request Forgery
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.