Cybersecurity researchers have found a new malware that leverages a genuine feature of Microsoft’s Internet Data Companies (IIS) to set up a backdoor in focused units.
In accordance to an advisory posted previous Thursday by Symantec, the malware, dubbed “Frebniis,” was made use of by a previously unfamiliar menace actor in opposition to targets in Taiwan.
“The method used by Frebniis involves injecting destructive code into the memory of a [dynamic link library] DLL file […] related to an IIS function utilised to troubleshoot and examine failed web web page requests,” reads the technical generate-up.
At a essential degree, IIS is a web server jogging on Windows devices to serve requested HTML internet pages or data files. These servers can accept requests from distant shopper personal computers and then return the correct response.
“IIS has a attribute acknowledged as Unsuccessful Ask for Party Buffering (FREB) that collects knowledge and information about requests, this kind of as originating IP handle and port, HTTP headers with cookies, and many others.,” described the Symantec workforce.
In accordance to the security researchers, exploiting this software enabled the malware to stealthily observe all HTTP requests whilst also automatically recognizing specifically formatted HTTP requests sent by the attacker.
“These requests enable remote code execution [RCE] and proxying to inner systems in a stealthy way,” reads the advisory. “No information or suspicious processes will be operating on the procedure, making Frebniis a rather unique and exceptional sort of HTTP backdoor noticed in the wild.”
The Symantec team clarified that to use this strategy, an attacker would need to have to acquire access to the Windows process functioning the IIS server by some other signifies. In the attack described in the advisory, the security scientists wrote that it was unclear how this accessibility was realized.
This is not the initially time Microsoft’s IIS has been employed for malicious reasons. Back again in 2020, the tech giant patched their servers right after an improve in this variety of attack.
Extra not long ago, Microsoft unveiled patches for around 70 CVEs, which include three zero-day vulnerabilities.
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