CVE-2026-42578 Netty: HTTP Header Injection via HttpProxyHandler Disabled Validation
Attackers can inject arbitrary HTTP headers into CONNECT requests via Netty's HttpProxyHandler due to disabled validation, potentially bypassing proxy security controls.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42578?
CVE-2026-42578 is a low-severity vulnerability in Netty Netty, published on 13 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty's HttpProxyHandler constructs HTTP CONNECT requests with header validation explicitly disabled. The newInitialMessage() method creates headers using DefaultHttpHeadersFactory.headersFactory().withValidation(false), then adds user-provided outboundHeaders without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
Which versions are affected by CVE-2026-42578?
4 open source packages ship an affected version, including io.netty:netty-handler-proxy. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-handler-proxy Maven | All versions | 4.1.133.Final |
io.netty:netty-handler-proxy Maven | All versions | 4.1.133.Final |
io.netty:netty-handler-proxy Maven | From 4.2.0.Alpha1 | 4.2.13.Final |
io.netty:netty-handler-proxy Maven | From 4.2.0.Alpha1 | 4.2.13.Final |
Products include Netty Netty.
How do I fix CVE-2026-42578?
Upgrade io.netty:netty-handler-proxy to a fixed version for your release line: 4.1.133.Final or 4.2.13.Final.
Is CVE-2026-42578 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42578 exists.
Other vulnerabilities in Netty Netty
- CVE-2026-75595 Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
- CVE-2026-75596 Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
- CVE-2026-59901 Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang
- CVE-2026-55851 Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion
- CVE-2026-56745 Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion
Sources
Also known as CLEANSTART-2026-AX30429, CLEANSTART-2026-BZ01230, CLEANSTART-2026-KM45055, CLEANSTART-2026-UR63455, DEBIAN-CVE-2026-42578, ECHO-46e7-3ee7-0488 and 82 more.