CVE-2026-69217 Http4s - HTTP Request Smuggling

Http4s prior to 0.23.35 and 1.0.0-M47 contains an HTTP request smuggling vulnerability caused by accepting differing duplicate Content-Length headers and using the last value, letting unauthenticated attackers bypass front-end controls and poison caches, exploit requires attacker to send crafted CL.CL requests.

CVSS base score 8.7 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.50% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
HTTP Request Smuggling
Impact
Man In The Middle
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
Published
15 September 2026
Updated
15 October 2026
Weakness
CWE-444

Vendor fix

Upgrade to versions 0.23.35 or 1.0.0-M47 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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