"Sinkclose" Vulnerability Affects Every AMD CPU Dating Back to 2006
A critical security flaw known as "Sinkclose" (CVE-2023-31315) has been identified in all AMD processors dating back to 2006, potentially affecting hundreds of millions of devices worldwide. This vulnerability allows malicious actors to exploit the chip architecture, leading to unauthorized access to sensitive data. Researchers Enrique Nissim and Krzysztof Okupski, researchers from the security firm IOActive, have revealed that the vulnerability can be exploited through various methods, enabling attackers to extract confidential information from affected systems, including passwords and personal data. The issue is especially concerning, given that it is present in all AMD CPUs made in the last 18 years and their widespread use in both consumer and enterprise environments. However, to exploit this vulnerability, an attacker must possess access to system's kernel. Downloading of malware-infused files can trigger it, so general safety measures are recommended.
The Sinkclose method exploits a little-known capability in AMD processors called TClose. This name is a blend of "TClose" and "Sinkhole," with the latter referring to a previous vulnerability found in Intel's System Management Mode in 2015. AMD chips employ a protective mechanism named TSeg, which blocks operating systems from accessing a specific memory area reserved for System Management Mode (SMM), known as System Management Random Access Memory (SMRAM). However, the TClose feature is designed to maintain backward compatibility with older hardware that might use the same memory addresses as SMRAM. It does this by remapping memory when activated. The security experts discovered that they could manipulate this TClose remapping function using only standard operating system permissions. By doing so, they could deceive the SMM into retrieving altered data, enabling them to redirect the processor and run their own instructions with the high-level privileges of SMM. This technique essentially allows attackers to bypass standard security measures and execute malicious code at one of the most privileged levels of the processor, potentially compromising the entire system.
The Sinkclose method exploits a little-known capability in AMD processors called TClose. This name is a blend of "TClose" and "Sinkhole," with the latter referring to a previous vulnerability found in Intel's System Management Mode in 2015. AMD chips employ a protective mechanism named TSeg, which blocks operating systems from accessing a specific memory area reserved for System Management Mode (SMM), known as System Management Random Access Memory (SMRAM). However, the TClose feature is designed to maintain backward compatibility with older hardware that might use the same memory addresses as SMRAM. It does this by remapping memory when activated. The security experts discovered that they could manipulate this TClose remapping function using only standard operating system permissions. By doing so, they could deceive the SMM into retrieving altered data, enabling them to redirect the processor and run their own instructions with the high-level privileges of SMM. This technique essentially allows attackers to bypass standard security measures and execute malicious code at one of the most privileged levels of the processor, potentially compromising the entire system.
