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FiveSys Rootkit Exploits Microsoft-Issued Digital Signature

Microsoft revoked the signature for FiveSys, after being informed of the abuse.


A rootkit termed FiveSys can potentially avoid detection and enter Windows users' PCs by abusing a Microsoft-issued digital signature, as per the Bitdefender security experts, 

Microsoft introduced rigorous requirements for driver packages that aim to receive a WHQL (Windows Hardware Quality Labs) digital signature to prevent certain types of malicious attacks, and starting with Windows 10 build 1607, it prevents kernel-mode drivers from being loaded without such a certificate. 

Malware developers, on the other hand, seem to have discovered a way to bypass Microsoft's certification and obtain digital signatures for their rootkits, allowing them to target victims without raising suspicion. 

Microsoft confirmed in June that intruders had successfully submitted the Netfilter rootkit for certification via the Windows Hardware Compatibility Program. Now, Bitdefender's researchers warn that the FiveSys rootkit also has a Microsoft-issued digital signature, implying that this might soon become an emerging trend in which adversaries successfully verify their malicious drivers and signed by Microsoft. 

According to the researchers, FiveSys is comparable to the Undead malware that was first disclosed a few years ago. Furthermore, the rootkit, like Netfilter, is aimed towards the Chinese gaming industry. 

Bitdefender stated, “The attackers seem to originate from China and target several domestic games. We can confidently attribute this campaign to several threat actors, as their tools share the same functionality but are vastly different in implementation.” 

The rootkit directs Internet traffic to a custom proxy server using a frequently updated autoconfiguration script that comprises a list of domains/URLs. Furthermore, the rootkit can prohibit drivers from the Netfilter and fk_undead malware families from being loaded by using a list of digital signatures. 

Moreover, FiveSys offers a built-in list of 300 supposedly randomly created domains that are encrypted and are intended to circumvent possible takedown attempts. Bitdefender also claims to have discovered multiple user-mode binaries that are used to obtain and execute malicious drivers on target PCs. 

FiveSys appears to use four drivers in all, although only two of them were isolated by the security experts. After discovering the abuse, Microsoft cancelled FiveSys' signature.

While the rootkit is being used to steal login credentials from gaming accounts, it is likely that it may be utilised against other targets in the future. However, by following a few easy cybersecurity safeguards, one can prevent falling prey to such or similar assaults.

Botezatu recommended,  "In order to stay safe, we recommend that users only download software from the vendor's website or from trusted resources. Additionally, modern security solutions can help detect malware – including rootkits – and block their execution before they are able to start." 
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