Security researchers at Damballa Willis McDonald and Loucif Kharouni have conducted a deep analysis of the wiper used by threat actors in the Sony Pictures hack. The experts discovered that attackers used a highly sophisticated disk-cleaning code dubbed Destover malware that stayed hidden using newly-uncovered anti-forensics tools.
The experts noticed significant improvements in the variant of Destover malware that was used to erased data across systems at Sony Pictures in November. In December security experts at Kaspersky Lab have detected a strain of Destover Malware that has been digitally signed with the certificates stolen during Sony attack.
Experts at Damballa have discovered that the new variant of Destover use components to avoid detection and make hard forensic investigations, for example the strain of malware analyzed by McDonald and Kharouni has the ability to change file timestamps and erase the logs.
“The Destover trojan is a wiper that deletes files off of an infected system, rendering it useless … for ideological and political reasons not for financial gain,” the pair of researchers say. “
“Much was revealed In the weeks and months following these breaches, except for how attackers were able to stay undetected within the network long enough to expand their presence and exfiltrate Terabytes of sensitive information. While researching a newer sample of Destover, we came across two files that were identified by one antivirus product at the time under a generic signature. After analyzing further, we found two utilities closely related to Destover. Both utilities would be used during an attack to evade detection while moving laterally through a network to broaden the attack surface. Both utilities had usage statements and were named as setMFT and afset.”
The experts discovered two utilities used to manipulate the timestamps and wipe logs. The utility setMFT is used for timestomping, a term used to identify the copy the timestamp settings from a source file on disk to a destination file.
“setMFT is used to copy the timestamp settings from a source file on disk to a destination file, also called timestomping. Timestomping combined with similar file naming enables a file to blend in with legitimate files in the same directory. This can conceal a file’s existence from security personnel looking for malicious files or scans of files created after a certain date. Timestomping can get past a cursory check for malicious files. A thorough forensic examination will reveal that a file has been timestomped based on conflicting record dates and possibly log files.” states the post published by Damballa.
The afset utility is used to wipe Windows logs based on time and identity, and modify an executable’s properties, including build time and checksum.
“afset, like setMFT is also used to timestomp files plus clean Microsoft Windows logs based on criteria (id, time) from the user. It also changes the PE build time and checksum. afset provides more granular functionality to allow the user to set only certain timestamps on a file (sia, fna or both). “
The experts have no doubt, attackers behind the Destover-based attacks are very well organized, afset and setMFT utilities are part of their arsenal and allow them to remain under the radar for a long period.
“Gaining a foothold inside the victim’s network is a top priority. History tells us that in most of the high-profile hacks making news headlines, the attackers were able to spend months hidden inside the victim’s network exfiltrating Terabytes of data.”
The table below details the different steps attackers would go through to penetrate the targeted infrastructure, it is possible to note that they have used the two utilities for different purposes and at different steps.
|Reconnaissance||Scanners, Open source intelligence gathering|
|Foothold||afset, setMFT, RATs, credential theft|
|Move laterally||Stolen administrative credentials and RATs|
|Exfiltrate||VPN accounts, RATs, out of band comms|
|Delete tracks||afset, setMFT, Destover / Shamoon|
|Exit||Publish stolen data, clean with Destover / Shamoon|