The vulnerability in Undertow's ChunkReader stems from an internal bitmask overlap where a single variable holds both chunk size and state flags. By sending an HTTP request with an oversized chunk size, an attacker can cause these values to overlap, tricking the parser into prematurely ending the first request. This enables HTTP request smuggling, leading to request desynchronization and potential bypass of security controls. The issue affects Red Hat products using Undertow, including WildFly and JBoss EAP. Red Hat rates the severity as moderate and notes that exploitation requires a frontend proxy to forward non-standard chunk sizes. Currently, no mitigation or patch meets Red Hat's standards for ease of use, applicability, or stability.

Successful exploitation allows an attacker to perform HTTP request smuggling, causing request desynchronization. This can lead to bypassing security controls such as firewalls or web application protections. The vulnerability impacts integrity by allowing unauthorized request manipulation but does not affect confidentiality or availability. Exploitation requires a specific network setup involving a frontend proxy forwarding crafted requests.

As per the Red Hat advisory, no mitigation or patch currently meets the criteria for ease of use, widespread applicability, or stability. Users should monitor the Red Hat advisory for updates on fixes or mitigations. Red Hat recommends upgrading to a supported product version with a fix once available. Customers with a Technical Account Manager (TAM) can consult directly for guidance. Until a fix is released, mitigating this vulnerability may not be feasible.