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Fencer Intel
high 8.7

CVE-2026-69217 json

Http4s: Ember Server accepts duplicate Content-Length headers

published 4mo ago modified last mo. also EUVD-2026-79193 , GHSA-p83c-4wj9-p6w9

Unreviewed: the maintainers' own advisory

Published by the maintainers on their GitHub repository http4s/http4s. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.

cvss
8.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits
0
none known

Summary

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, Ember’s HTTP/1.1 parser accepts differing duplicate Content-Length headers and uses the last value instead of rejecting the message. When an Ember server is behind a keep-alive intermediary that selects a different occurrence, an unauthenticated attacker can create CL.CL request smuggling that bypasses front-end controls, captures a later user’s headers, or poisons a cache. The shared client parser can also misframe responses from a malicious or compromised upstream when the client acts as a proxy for multiple downstream consumers. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

Patch / fix

  • typelevel http4s 0.23.35, 1.0.0-M47
  • org.http4s http4s-ember-core_2.12 0.23.35
  • org.http4s http4s-ember-core_2.13 0.23.35, 1.0.0-M47
  • org.http4s http4s-ember-core_3 0.23.35, 1.0.0-M47

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
last mo.

Exploit prediction

0.50% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-11).

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

Affected products

  • http4s http4s

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

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.

The maintainers of http4s/http4s published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.