For those who followed the GoldenSpy story last week from Trustwave, where tax software from China-based Aisino was used as a backdoor to gain access to the networks of foreign firms doing business with a Chinese bank, there's an interesting wrinkle.
While doing a routine follow-up investigation in a sandbox after last week's initial disclosure, Trustwave researchers found that after being discovered, Aisino sent software out with one mission in mind: to delete GoldenSpy with an uninstaller and remove any trace it existed.
Brian Hussey, Trustwave's vice president of cyber threat detection and response, says this new development was significant because it confirmed for the research team that Aisino knew about GoldenSpy and was looking to take it down after the initial news came out last week. However, it's unclear whether Aisino was culpable.
"It's a possibility Aisino sent the uninstaller as a way to clean up the issue after seeing the media exposure," Hussey says. "The secret removal is somewhat suspicious, but perhaps their risk mitigation plan decided this was the best possible method."
The new software deleted registry and log entries, all files and folders – including the GoldenSpy log file – and then finally deleted itself with the uninstaller, Hussey says. Aisino sent the uninstaller in two different waves. First, on June 28 the researchers discovered Aisino sent the uninstaller as an AWX.EXE file, but the variables were in plaintext, so it was easy for antivirus software to pick up. Hussey says they must have realized that antivirus software was picking up their activities, so a day later they sent an uninstaller as a BWXT.EXE file. The advantage there was that they sent the variables with Base64 encoding.
"Trustwave can't verify the reason for this change, but we hypothesize that it may have been to evade antivirus," Hussey says. "People have to realize that even though they were uninstalling the GoldenSpy malware, they still can use the tax software as a platform to launch future attacks. What's to say they couldn't wait three to five months after the news about GoldenSpy dies down and strike at a later point?"
Ron Hayman, chief cloud officer at AVANT, says he didn't think Aisino was responsible for injecting the malware on to its tax software.
"I think they launched the uninstaller to cover their tracks," Hayman says. "This case proves that the human element is still important. The level of sophistication the [attackers] had to make changes so quickly wouldn't have been picked up by most standard network security devices."
Trustwave's Hussey says companies with endpoint detection and response (EDR) capabilities should go back and see if there's any evidence that GoldenSpy existed on their network.
"The malware may not be there anymore, but companies really need to run an investigation," he says. "They need to find out if GoldenSpy was used to steal any data or if it created new users."
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