The package org.eclipse.milo:sdk-server before 0.6.8 are vulnerable to Denial of Service (DoS) when bypassing the limitations for excessive memory consumption by sending multiple CloseSession requests with the deleteSubscription parameter equal to False.

Affected: Maven: org.eclipse.milo:sdk-server

### Impact

Denial of Service

### Details

OPC UA specification describes a concept named _Subscriptions_. _Subscriptions_ monitor a set of _Monitored Items_ for _Notifications_ and return them to the _Client_ in response to _Publish_ requests. The server notifies the client about changes only in case the value is changed. Each monitored item is configured on a subscription, each subscription is linked to a single OPC UA session. Most OPC UA implementations set many controls and limitations for excessive memory consumption. For example:

* What is the maximum allowed number of concurrent sessions * For each active sessions - what is the maximum allowed number of concurrent subscription per a single session * For each active subscription - what is the maximum allowed number of concurrent monitored items per a single subscription

Clarity Research discovered a unique way to bypass those restrictions and fill up the OPC UA server process memory.

The close session request closes a connected session. A `deleteSubscription` flag is also sent in that message and determines whether the server should save the subscriptions for a future session reconnection or discard them upon session termination. If the `deleteSubscription` flag is `False` the server will store the subscriptions thus filling up the memory in an unlimited manner.

Sending multiple subscribe requests with multiple monitored items from multiple sessions will quickly fill up the process memory until the server crashes…

sdk-server: Denial of Service reactor-netty-http: Log request headers in some cases of invalid HTTP requests apache-commons-text: variable interpolation RCE