CVE-2026-90678 HAProxy - HTTP Request Smuggling

HAProxy 3.3.0 through 3.4.4 and 3.5-dev1 through 3.5-dev5 contain an HTTP request smuggling vulnerability caused by improper handling of HTTP/3 DATA frame lengths in chunked transfer coding on reused HTTP/1.1 backend connections, letting remote unauthenticated clients smuggle requests past frontend rules, exploit requires HTTP/3 frontend with QUIC support and specific backend conditions.

CVSS base score 7.5 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.77% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
HTTP Request Smuggling
Impact
Broken Access Control
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:L
Published
13 September 2026
Updated
15 October 2026
Weakness
CWE-130

Vendor fix

Upgrade to a version later than 3.4.4 or 3.5-dev5 or the latest available version.

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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