CVE-2021-41084

HIGHNVD 8.78.7
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This high-severity CVE scores 8.7 under NVD CVSS v3. EPSS exploit probability: 1.2% (68th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
Trending — 3 sources updated this week
8.7EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1.2%CVSS: 8.7Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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.nameå), 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 v3
8.7
EG Score
8.7HIGHmedium confidence
EG Risk
40
EG Risk 40/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity87% × 45%
Impact severity (EG Severity): CVSS 8.7 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation1.2% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's BOD 26-04 default: no one has published Automatable for this CVE, and CISA treats it as “no” for a CVE not in KEV.
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
1.2%
EPSS %ILE
68th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (8.7): severity, escalated by confirmed exploitation. This CVE's 8.7 is its impact severity (EG Severity), not escalated.

EG Severity
8.7 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
1.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-20). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

September 21, 2021

Last Modified

November 21, 2024

Advisory Details (4)

Auto-updated Sep 1, 2026
Patch available. Sources: github_commit, github.
Web page

HTTP Response Splitting | OWASP Foundation

https://owasp.org/www-community/attacks/HTTP_Response_Splitting
GitHub advisoryMentions a patch (unverified)

Response Splitting from unsanitized headers · Advisory · http4s/http4s · GitHub

https://github.com/http4s/http4s/security/advisories/GHSA-5vcm-3xc3-w7x3
GitHub commit Patch Available

commit d02007db1da4 (http4s/http4s)

Patch available: http4s/http4s v1.0.0-M39 (contains commit d02007db1da4)

https://github.com/http4s/http4s/commit/d02007db1da4f8f3df2dbf11f1db9ac7afc3f9d8

Affected Packages

(9 across 1 ecosystem)
Maven(9)
PackageVulnerable rangeFix by version rangeDependents
org.http4s:http4s-client_2.120.23.0, 0.23.1, 0.23.2, 0.23.3
  • every version up to 0.21.29: fixed in 0.21.29
  • 0.22.0 up to 0.22.5: fixed in 0.22.5
  • 0.23.0 up to 0.23.4: fixed in 0.23.4
—
org.http4s:http4s-client_2.130.23.0, 0.23.1, 0.23.2, 0.23.3
  • every version up to 0.21.29: fixed in 0.21.29
  • 0.22.0 up to 0.22.5: fixed in 0.22.5
  • 0.23.0 up to 0.23.4: fixed in 0.23.4
—
org.http4s:http4s-client_30.23.0, 0.23.1, 0.23.2, 0.23.3
  • every version up to 0.21.29: fixed in 0.21.29
  • 0.22.0 up to 0.22.5: fixed in 0.22.5
  • 0.23.0 up to 0.23.4: fixed in 0.23.4
—
org.http4s:http4s-server_2.100.10.0 ... 0.9.3 (131 versions)
  • every version through 0.21.28: no fix on record
—
org.http4s:http4s-server_2.110.10.0 ... 0.9.3 (220 versions)
  • every version through 0.21.28: no fix on record
—
org.http4s:http4s-server_2.120.23.0, 0.23.1, 0.23.2, 0.23.3
  • every version up to 0.21.29: fixed in 0.21.29
  • 0.22.0 up to 0.22.5: fixed in 0.22.5
  • 0.23.0 up to 0.23.4: fixed in 0.23.4
—
org.http4s:http4s-server_2.130.23.0, 0.23.1, 0.23.2, 0.23.3
  • every version up to 0.21.29: fixed in 0.21.29
  • 0.22.0 up to 0.22.5: fixed in 0.22.5
  • 0.23.0 up to 0.23.4: fixed in 0.23.4
—
org.http4s:http4s-server_2.13.0-M50.20.0 ... 0.20.9 (12 versions)
  • every version through 0.21.28: no fix on record
—
org.http4s:http4s-server_30.23.0, 0.23.1, 0.23.2, 0.23.3
  • 0.22.0 up to 0.22.5: fixed in 0.22.5
  • 0.23.0 up to 0.23.4: fixed in 0.23.4
—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 10× in last 7d / 37× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 95 of 201 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 5 repeat rows among the latest 100 are merged into the row they repeat. The 106 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-23 16:28 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  2. 2026-10-22 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  3. 2026-10-21 16:28 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  4. 2026-10-21 09:00 UTCEG score recompute
  5. 2026-10-20 16:28 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  6. 2026-10-19 16:28 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  7. 2026-10-18 16:28 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  8. 2026-10-18 08:54 UTCEG score recompute
  9. 2026-10-17 22:25 UTCOSV refresh
  10. 2026-10-17 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  11. 2026-10-16 16:34 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  12. 2026-10-15 16:28 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  13. 2026-10-14 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  14. 2026-10-13 16:28 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  15. 2026-10-12 19:10 UTCEG score recompute
  16. 2026-10-12 16:30 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  17. 2026-10-11 23:35 UTCEG score recompute
  18. 2026-10-11 13:44 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  19. 2026-10-10 19:56 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  20. 2026-10-09 20:04 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  21. 2026-10-08 16:40 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  22. 2026-10-07 23:45 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  23. 2026-10-06 15:14 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  24. 2026-10-05 17:40 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  25. 2026-10-04 23:19 UTCEPSS rescoreEPSS 1.2% · 68th percentile
Show 70 more
  1. 2026-10-03 14:22 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  2. 2026-10-02 16:23 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  3. 2026-10-01 19:46 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  4. 2026-09-30 15:41 UTCEG score recompute
  5. 2026-09-30 15:00 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  6. 2026-09-29 15:15 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  7. 2026-09-28 13:47 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  8. 2026-09-27 13:41 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  9. 2026-09-26 15:54 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  10. 2026-09-26 00:21 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  11. 2026-09-25 16:45 UTCOSV refresh
  12. 2026-09-24 14:00 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  13. 2026-09-23 13:44 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  14. 2026-09-22 14:44 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  15. 2026-09-21 20:28 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  16. 2026-09-20 20:13 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  17. 2026-09-19 15:38 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  18. 2026-09-18 19:23 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  19. 2026-09-17 19:23 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  20. 2026-09-16 14:05 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  21. 2026-09-15 03:06 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  22. 2026-09-12 14:57 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  23. 2026-09-11 14:49 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  24. 2026-09-11 09:33 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  25. 2026-09-08 21:56 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  26. 2026-09-07 15:58 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  27. 2026-09-06 13:45 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  28. 2026-09-06 07:22 UTCOSV refresh
  29. 2026-09-05 15:25 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  30. 2026-09-04 13:57 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  31. 2026-09-04 05:03 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  32. 2026-09-02 14:09 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  33. 2026-09-01 13:50 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  34. 2026-09-01 03:33 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  35. 2026-08-30 19:14 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  36. 2026-08-30 01:19 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  37. 2026-08-28 21:37 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  38. 2026-08-27 14:22 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  39. 2026-08-26 14:43 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  40. 2026-08-25 13:46 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  41. 2026-08-24 14:13 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  42. 2026-08-23 00:16 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  43. 2026-08-21 23:46 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  44. 2026-08-20 22:52 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  45. 2026-08-19 17:58 UTCOSV refresh
  46. 2026-08-19 17:01 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  47. 2026-08-18 13:45 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  48. 2026-08-17 13:44 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  49. 2026-08-16 14:53 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  50. 2026-08-16 02:11 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  51. 2026-08-15 01:27 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  52. 2026-08-13 21:57 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  53. 2026-08-12 13:48 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  54. 2026-08-11 13:38 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  55. 2026-08-09 13:44 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  56. 2026-08-08 16:33 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  57. 2026-08-07 16:24 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  58. 2026-08-06 13:44 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  59. 2026-08-05 19:14 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  60. 2026-08-04 13:29 UTCOSV refresh
  61. 2026-08-04 10:34 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  62. 2026-08-03 10:33 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  63. 2026-08-02 02:24 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  64. 2026-08-01 04:13 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  65. 2026-07-30 16:25 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  66. 2026-07-30 01:28 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  67. 2026-07-28 15:33 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  68. 2026-07-26 14:52 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  69. 2026-07-25 14:15 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  70. 2026-07-24 14:15 UTCEPSS rescoreEPSS 1.2% · 65th percentile

Frequently asked(5)

What is CVE-2021-41084?
CVE-2021-41084 is a high-severity vulnerability; its CVE record was published on September 21, 2021. 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.nameå), Header values (Header.value), Status reason phrases…
When was the CVE record for CVE-2021-41084 published?
The CVE record for CVE-2021-41084 was published on September 21, 2021. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of November 21, 2024; the record at its source may have been updated since.
Is CVE-2021-41084 actively exploited?
CVE-2021-41084 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.2% probability of exploitation in the next 30 days (68th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-41084?
CVE-2021-41084 has a CVSS v3 base score of 8.7 (NVD).
How do I remediate CVE-2021-41084?
A fix for CVE-2021-41084 is available: update to the fixed version the vendor names in its advisory.

Dependency Blast Radius

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