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Fencer Vulns
critical 9.2

CVE-2026-69204 json

Http4s: Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)

published 2026-09-15 54 d ago modified 2026-09-16 53 d ago also GHSA-8h4c-x2wg-6xp8 , EUVD-2026-79025

cvss
9.2
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 47%
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 HTTP/1.1 does not reject messages containing both Transfer-Encoding and Content-Length, so an intermediary and Ember can select different body framing rules. When ember-server is behind a keep-alive intermediary that forwards both headers and frames by Content-Length, an unauthenticated attacker can smuggle a second request, bypass intermediary access controls, poison caches, or cause a victim request to be joined to an attacker-controlled prefix. The shared response parser can also desynchronize an ember-client connection when a malicious or compromised upstream sends both headers. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

Patch / fix

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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
54 d ago

Exploit prediction

0.57% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 9.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N
CNA 4.0 9.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem package affected fixed in
maven org.http4s:http4s-ember-core_2.12
<0.23.35
0.23.35
maven org.http4s:http4s-ember-core_2.13
<0.23.35
>=1.0.0-M1, <1.0.0-M47
0.23.35
1.0.0-M47
maven org.http4s:http4s-ember-core_3
<0.23.35
>=1.0.0-M1, <1.0.0-M47
0.23.35
1.0.0-M47

Affected products

  • http4s http4s

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns 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.