CVE-2026-56746 Netty has a Security Control Bypass via CORS Short-Circuit Failure
Attackers can bypass CORS short-circuit protections in Netty by sending a null Origin header, allowing unauthorized requests to reach backend applications.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-56746?
CVE-2026-56746 is a medium-severity vulnerability in Netty Netty, published on 21 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Netty is a network application framework for development of protocol servers and clients. Versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final, are vulnerable to security control bypass during the origin evaluation process. CorsHandler provides a shortCircuit() configuration designed to reject unauthorized cross-origin requests immediately, acting as a security control before requests reach the application. However, due to a logical operator error in the origin evaluation process, this protection can be entirely bypassed. An attacker can bypass the short-circuit mechanism by sending a request with an Origin: null header. This failure forwards unauthorized requests to the backend application, bypassing intended access controls. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.
Weakness: CWE-284
Which versions are affected by CVE-2026-56746?
4 open source packages ship an affected version, including io.netty:netty-codec-http. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-codec-http Maven | All versions | 4.1.136.Final |
io.netty:netty-codec-http Maven | All versions | 4.1.136.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Final | 4.2.16.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Final | 4.2.16.Final |
Products include Netty Netty.
How do I fix CVE-2026-56746?
Upgrade io.netty:netty-codec-http to a fixed version for your release line: 4.1.136.Final or 4.2.16.Final.
Is CVE-2026-56746 being exploited?
There is no known exploitation of CVE-2026-56746 in the wild and no public exploit code.
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-BA81930, CLEANSTART-2026-DA58471, CLEANSTART-2026-MB96897, CLEANSTART-2026-QY68348, CLEANSTART-2026-YD90656, DEBIAN-CVE-2026-56746 and 108 more.