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Date: Sat, 18 Dec 2021 11:30:16 +0100
From: Moritz Bechler <>
Subject: Re: CVE-2021-45046: Apache Log4j2 Thread Context
 Message Pattern and Context Lookup Pattern vulnerable to a denial of service


> For =2.15 this is mostly mitigated by the fact protocol and target host 
> to which lookups are possible are also restricted to localhost by 
> default. There still seems to be a way to hang/crash the process, thou.

Updating that for completeness: a bypass of that hostname restriction 
was found by Alvaro Munoz, exploiting different URI interpretations by 
the standard Uri class and JNDI.
Therefore 2.15 can be vulnerable again for RCE, if a layout
with attacker-controlled input outside the message is used or the 
expression lookup has been re-enabled.

This also requires resolving a DNS name like or 
localhost#x.y.z, which some resolvers and likely recursors will directly 


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