Undertow Uncontrolled Resource Consumption Vulnerability - CVE-2022-2053

When a POST request comes through AJP and the request exceeds the max-post-size limit (maxEntitySize) Undertow39s AjpServerRequestConduit implementation closes a connection without sending any response to the client/proxy. This behavior results in that a front-end proxy marking the backend worker (application server) as an error state and not forward requests to the worker for a while. In mod_cluster this continues until the next STATUS request (10 seconds intervals) from the application server updates the server state. So in the worst case it can result in quotAll workers are in error statequot and mod_cluster responds quot503 Service Unavailablequot for a while (up to 10 seconds). In mod_proxy_balancer it does not forward requests to the worker until the quotretryquot timeout passes. However luckily mod_proxy_balancer has quotforcerecoveryquot setting (On by default this parameter can force the immediate recovery of all workers without considering the retry parameter of the workers if all workers of a balancer are in error state.). So unlike mod_cluster mod_proxy_balancer does not result in responding quot503 Service Unavailablequot. An attacker could use this behavior to send a malicious request and trigger server errors resulting in DoS (denial of service). This flaw was fixed in Undertow 2.2.19.Final Undertow 2.3.0.Alpha2.