Researchers have uncovered a previously unknown malicious IIS module, dubbed Owowa, that steals credentials when users log into Microsoft Outlook Web Access.
“The particular danger with Owowa is that an attacker can use the module to passively steal credentials from users who are legitimately accessing web services,” he explained.
The malicious module can be loaded by a cyberattacker that has initial access to the server environment, researchers explained.
“The module is first registered in the global assembly cache, and can then be loaded by the IIS server that is running the OWA application,” according to Kaspersky.
If the OWA username is Fb8v91c6tHiKsWzrulCeqO, the malicious module deletes the content of the encrypted credentials log, and returns the OK string;.
Malicious IIS modules, and Owowa in particular, can be identified by using the command “Appcmd.exe” or the IIS configuration tool, which lists all the loaded modules on a given IIS server.