Security Experts:

RSA: Citadel Trojan Armed With New Feature

The makers of the notorious Citadel Trojan continue to innovate, this time adding a new feature designed to help botmasters have smoother interactions with their victims.

Built off the Zeus source code, the October release of v1.3.4.1 "Rain Edition" of the malware costs nearly $3,400 off the shelf, according to EMC's RSA security division. The new version has been enhanced with a simplified interface to accommodate new users and to alleviate the amount of work by Citadel's support staff. But perhaps even more importantly, the latest version of the malware has been armed with a new feature known as "Dynamic Config" that enables botmsters to have quicker interactions with infected victims through browser injection technology.

"This nifty function allows Trojan operators to create web injections and use them on the fly, pushing them to selected bots without the hassle of pushing/downloading an entire new configuration file," explained Limor Kessem, a cyber intelligence expert at RSA.

"Citadel-infected machines are going to have an instruction to reach out to the C&C every two minutes and update themselves with a predefined file where injection “packs” will be ready to go," she continued. "The whole system will be managed by a clever distribution mechanism dictating which injection(s) go to which bot or group of bots. The format will be fully “Zeus-compatible,” of course."

This will not cancel out the configuration file or the injections it already contains, she added, and botmasters can choose whether to use both simultaneously. If an injection in the usual config already has a more recent version, the newest will automatically be used.

"The new mechanism is designed right into Citadel’s Fraud-as-a-Service model," she blogged. "Botmasters will be able to grant limited access to hired help. Up to five blackhat programmers (per admin) will be afforded a username and password combination to their own section on the administration panel. The injection sellers could create and save their work, get paid by the piece, and work with multiple botmasters – FaaS [fraud-as-a-service] at its best!"