A proof of concept (PoC) enables security researchers to make their point, in code, about an exploit. By showing how a particular code might execute, researchers can illuminate the underlying root cause of a situation.

Unfortunately, malware authors can also create a PoC exploit as the basis of weaponized code to carry out an attack. This week, a gang of cybercrooks did just that.

Sundown Develops PoC Exploit

Threatpost reported that a PoC developed by Texas-based security research firm Theori has been used in the Sundown exploit kit (EK). The PoC exposed two vulnerabilities found in the Microsoft Edge browser.

Although Microsoft patched these specific vulnerabilities in November, researchers spotted code in Sundown using the PoCs only two days after they were made public. Interestingly, this was the first change in Sundown’s overall code that researchers had witnessed in over six months, Threatpost noted.

Theori found vulnerabilities in the Chakra JavaScript engine, which has been around since Internet Explorer 9. The PoC showed how the engine can trigger an information leak, which then leads to remote code execution (RCE). The Sundown EK uses this RCE exploit to drop its malicious payload.

More PoC Problems

Unfortunately for security research, a well-intentioned PoC may also highlight vulnerabilities that were not part of its initial focus. One such PoC from Laurent Gaffié, for example, was looking at a distributed denial-of-service (DoS) vulnerability in Local Security Authority Subsystem Service (LSASS), which enforced Windows security policy. SecurityWeek noted that this might cause the system to become unresponsive if sent specially crafted requests.

Even though a patch was released for this vulnerability in November, the story didn’t end there. Nicolas Economou, a security researcher from Core Security, discovered that a similar problem was actually being triggered by the exploit. He was understandably confused as to why the DDoS PoC was not working as intentioned on a Windows 10 system.

“There was a misunderstanding here about the vulnerability,” Economou wrote, “because, according to the PoC released by Laurent Gaffié, the problem wasn’t in the structure pointer, but rather in one field of the CRITICAL_SECTION object pointed by this structure, which is null when the huge allocation fails.”

This analysis prompted Microsoft to release a new security bulletin, which included a patch for the affected systems.