Summary
Netty's 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.
Details
In io.netty.handler.codec.http.cors.CorsHandler#channelRead, the short-circuit logic relies on the configuration returned by getForOrigin(origin) to determine if an origin is authorized. If getForOrigin returns a configuration object, the short-circuit check (!(origin == null || config != null)) is bypassed, and the request proceeds to the backend.
The vulnerability is located in the getForOrigin method:
if (corsConfig.isNullOriginAllowed() || NULL_ORIGIN.equals(requestOrigin)) {
return corsConfig;
}If an attacker sends Origin: null, NULL_ORIGIN.equals(requestOrigin) evaluates to true. The method returns the configuration object regardless of whether isNullOriginAllowed() was configured by the developer. The short-circuit is bypassed.
Impact
Applications relying on CorsHandler's short-circuit feature to prevent unauthorized cross-origin requests from reaching their backend logic are completely exposed. The framework fails to enforce the developer's intended access controls, allowing unauthorized requests to be processed.
References
violetagg Reporter
Summary
Netty's 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 anOrigin: nullheader. This failure forwards unauthorized requests to the backend application, bypassing intended access controls.Details
In
io.netty.handler.codec.http.cors.CorsHandler#channelRead, the short-circuit logic relies on the configuration returned bygetForOrigin(origin)to determine if an origin is authorized. IfgetForOriginreturns a configuration object, the short-circuit check(!(origin == null || config != null))is bypassed, and the request proceeds to the backend.The vulnerability is located in the
getForOriginmethod:If an attacker sends
Origin: null,NULL_ORIGIN.equals(requestOrigin)evaluates to true. The method returns the configuration object regardless of whetherisNullOriginAllowed()was configured by the developer. The short-circuit is bypassed.Impact
Applications relying on CorsHandler's short-circuit feature to prevent unauthorized cross-origin requests from reaching their backend logic are completely exposed. The framework fails to enforce the developer's intended access controls, allowing unauthorized requests to be processed.
References