Hackers Using Weaponized IIS Module to Stealing Credentials & Enabling RCE

Kaspersky security lab has recently identified a digital threat that installs malicious webserver IIS modules that work with Microsoft Exchange Outlook Web Access. 

These malicious IIS modules are capable of stealing credentials and data from devices as well as executing commands remotely.


This threat is dubbed “Owowa,” the first sample of this threat was detected at the end of 2020 when it was sent to VirusTotal security services.

Since then Owowa has undergone several extensive updates, with the latest version dating from April 2021. Owowa is a .NET v4.0 assembly that is developed with C#, the attacker loads it as a module within an IIS web server that uncovers the OWA (Exchange’s Outlook Web Access).

According to the Kaspersky report, In the OWA login page credentials that are entered by any user can be stolen, and not only that even it also allows its operators to run arbitrary code and commands remotely on the compromised server.

It is used primarily in attacks against the government servers, public transport, and other crucial services in countries like:-

  • Malaysia
  • Mongolia
  • Indonesia 
  • Philippines

Abilities of Owowa 

Owowa has been programmed by the hackers to log all the credentials that result in authorized access to infected Microsoft Exchange servers. 

However, after that the hackers start grabbing the following things:-

  • IP address
  • Username
  • Password
  • Login time

Here, after stealing the above things the hackers start encrypting them through RSA, and then the malicious agent controllers execute commands for their submissions.

OWA login error messages

Here we have mentioned below all the OWA login error messages that are present by the operators on the login page:-

  • if the OWA username is jFuLIXpzRdateYHoVwMlfc, Owowa will return the encrypted credentials log, encoded in base64;
  • if the OWA username is Fb8v91c6tHiKsWzrulCeqO, the malicious module deletes the content of the encrypted credentials log, and returns the OK string (encrypted using RSA);
  • If the OWA username is dEUM3jZXaDiob8BrqSy2PQO1, Owowa executes the command that is typed in the OWA password field using PowerShell on the compromised server. The result of the command is encrypted (as previously described) and returned to the operator.

The unusual type of attack on Microsoft Exchange servers is the main highlight of Owowa. From malicious web shells, all these codes are made and this also allows these codes to run on the platform.

Apart from this, in hosting configurations all these malicious IIS modules are used, and security solutions or AVs skip these malicious IIS modules, which makes them more stealthy and sophisticated.

Moreover, Kaspersky is still scrutinizing for ways to dissuade all these attacks, but here, the possible way to remove the infection is the removal of the malicious modules.

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Posted by Charlie