A recently discovered exploit kit (EK) has been used in a campaign targeting users in Japan, Korea, the Middle East, Southern Europe, and other countries in the Asia Pacific region.
Dubbed Fallout, the new EK has been targeting users in Japan with the SmokeLoader Trojan, but has been also observed delivering the GandCrab ransomware in the Middle East. Before dropping the payload, however, the EK fingerprints the browser profile to identify targets of interest.
Targeted users are redirected from a genuine advertiser page to the exploit kit landing page URL via multiple 302 redirects, FireEye’s security researchers have discovered.
Based on the user’s operating system and browser, the attack either delivered the EK directly or attempts to reroute the victim to other social engineering campaigns. macOS users in the United States, for example, are redirected to social engineering attempts posing either as anti-virus software or Flash updates.
“The strategy is consistent with the rise of social engineering attempts FireEye has been observing for some time, where bad actors use them to target users that are on fully patched systems or any OS/software profile that is not ideal for any exploit attempts due to software vulnerability,” the security firm notes.
The campaign, FireEye says, has been targeting entities in the government, telecom and healthcare sectors.
Fallout’s landing page only contained code for a VBScript vulnerability at first, but Flash embedding code was later added for it, the security researchers reveal. The VBScript loads a JScript function that decodes malicious next stage VBScript to exploit CVE-2018-8174 and executes shellcode that downloads, decrypts and executes a payload.
The dropped file contains PE loader code for initial loading and final payload execution. An unpacked DLL enumerates all running processes, creates their crc32 checksums, and tries to match them against a list of blacklisted checksums.
If any is found, the malware enters an infinite loop. If the check passes, a new thread is started. The malware checks its own image path, OS version, and architecture.
Depending on the Windows version and architecture, the malware attempts to take ownership of ctfmon.exe or rundll32.exe, or replace them with a copy of itself. It also adds itself to startup and reboots the system.
If it fails to replace the targeted system files successfully, the malware copies itself at a different location and then executes via ShellExecuteW.
The final payload in this attack is the GandCrab ransomware, which is being fetched and manually loaded into memory by the malware.
“In recent years, arrests and disruptions of underground operations have led to exploit kit activity declining heavily. Still, exploit kits pose a significant threat to users who are not running fully patched systems. Nowadays we see more exploit kit activity in the Asia Pacific region, where users tend to have more vulnerable software. Meanwhile, in North America, the focus tends to be on more straightforward social engineering campaigns,” FireEye concludes.