Security Experts:

NSA-Linked Implant Patched to Work on Windows Embedded

DoublePulsar, one of the hacking tools the Shadow Brokers supposedly stole from the National Security Agency (NSA)-linked Equation Group, can now run on Windows Embedded devices.

The backdoor was released publicly in April last year along with a variety of Windows exploits that Microsoft had patched the month before. It is a sophisticated, multi-architecture SMB (Server Message Block) backdoor that can stay well hidden on infected machines.

In addition to SMB, it is also used as the primary payload in RDP (Remote Desktop Protocol) exploits in the NSA’s FuzzBunch software (an exploitation framework that resembles Rapid7’s Metasploit).

As it turns out, although it would work on a wide range of Windows releases, DoublePulsar wouldn’t work on devices running a Windows Embedded operating system, even if the platform itself is vulnerable to the NSA-linked exploits, a security researcher who uses the online handler of Capt. Meelo says.

Windows Embedded, the researcher discovered, was indeed vulnerable to the exploits, but the relevant Metasploit modules wouldn’t work on it. Using FuzzBunch, however, he verified that the target device was indeed vulnerable via the EternalBlue exploit.

While exploitation via the EternalBlue module and the result were successful, the installation of DoublePulsar failed, so the researcher decided to analyze the implant to discover why.

What he found was that one simple line of code was enough to make it work on Windows Embedded.

DoublePulsar was designed to check the Windows version on the target machine and take one installation path on Windows 7 or another (and perform other OS checks) on other platform iterations. However, there was no check for Windows Embedded, which generated an error message.

By simply modifying an instruction in the “Windows 7 OS Check,” the researcher was able to force the implant into taking that specific installation path.

“To do this, I went to Edit > Patch program > Change byte. Then I changed the value 74 (opcode of JZ) to 75 (opcode of JNZ). I then created a DIF file by going to File > Produce file > Create DIF file,” Capt. Meelo explains.

Using a script from a security enthusiast who calls himself StalkR, he then patched the modified .exe file and then moved the modified Doublepulsar-1.3.1.exe back to its original location. This resulted in a successful injection of the generated DLL payload to the target host.

Related: One Year After WannaCry Outbreak, EternalBlue Exploit Still a Threat

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