From securelist.com
Following on from our earlier Owowa discovery, we continued to hunt for more backdoors potentially set up as malicious modules within IIS, a popular web server edited by Microsoft. And we didn’t come back empty-handed…
In 2021, we noticed a trend among several threat actors for deploying a backdoor within IIS after exploiting one of the ProxyLogon-type vulnerabilities within Microsoft Exchange servers. Dropping an IIS module as a backdoor enables threat actors to maintain persistent, update-resistant and relatively stealthy access to the IT infrastructure of a targeted organization; be it to collect emails, update further malicious access, or clandestinely manage compromised servers that can be leveraged as malicious infrastructure.