CVE-2026-100666

MEDIUM CVSS 4.0: 6.9 EPSS 0.24%
Updated Sep 30, 2026
Netty
Parameter Value
CVSS 6.9 (MEDIUM)
Affected Versions 4.2.0.final — 4.2.17.final
Fixed In 4.2.17
Type CWE-444
Vendor Netty
Public PoC No

Netty's HttpServerCodec (io.netty:netty-codec-http) in versions 4.2.0.Final through 4.2.16.Final and in versions up to and including 4.1.136.Final pairs each outbound response with an inbound request by calling pollMethod() once per response, including for 1xx informational responses. If a client pipelines an HTTP/1.1 GET carrying an Expect: 100-continue header followed by a HEAD request, the 100 Continue response consumes the queued GET method, so the subsequent 200 OK for the GET is paired with HEAD and its body is dropped, while the following 200 OK for the HEAD request is written with a body. This desynchronizes HTTP parsing on the connection: the GET entity is never delivered and the HEAD response body is interpreted as the GET body, resulting in response splitting and unsafe connection reuse.

Fixed in 4.2.17.Final and 4.1.137.Final.

Attack Parameters

Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Attack Requirements
None
No additional conditions
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed

Impact Assessment

Confidentiality
Low
Partial data leak
Integrity
Low
Partial data modification
Availability
Low
Partial disruption

CVSS Vector v4.0

Weakness Type (CWE)

Vulnerable Products 2

Configuration From (including) Up to (excluding)
Netty Netty
cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:*
4.2.0.final 4.2.17.final
Netty Netty
cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:*
— 4.1.137.final