CVE-2022-2053

When a POST request comes through AJP and the request exceeds the
max-post-size limit (maxEntitySize), Undertow’s 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 “All
workers are in error state” and mod_cluster responds “503 Service
Unavailable” for a while (up to 10 seconds). In mod_proxy_balancer, it does
not forward requests to the worker until the “retry” timeout passes.
However, luckily, mod_proxy_balancer has “forcerecovery” 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 “503 Service Unavailable”. 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.