Thanks for the write-up but I have a few questions. Why does log4j's .log() method attempt to parse the strings sent to it? It is the last thing I would expect it to do. Is the part in the sample code where the user's input is output back to them part of the exploit? If so how does it fit into the attack? What will the attacker see beyond the string they originally sent as input?
Could you update your mitigation steps to explain how to set the "log4g.formatMsgNoLookups" config? It's not clear whether this is a property that goes into the log4j config or into the JVM args.
Could you update your mitigation steps to explain how to set the "log4g.formatMsgNoLookups" config? It's not clear whether this is a property that goes into the log4j config or into the JVM args.