CVE-2026-56746: Netty has a Security Control Bypass via CORS Short-Circuit Failure

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-21 · updated 2026-07-30
Weakness: CWE-284

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.

Affected products

netty: from 4.1.0 before 4.1.136; from 4.2.0 before 4.2.16 — fixed in 4.1.136, 4.2.16

How to fix

Upgrade to a fixed version: netty 4.1.136, 4.2.16. Check the vendor advisory for mitigations.

References

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