Elastic Security Lab Determines Vulnerabilities in Microsoft's Smart App Control and SmartScreen Features
Windows 8 and Windows 11 come equipped with built-in security features designed to protect against malicious or untrusted applications: Microsoft SmartScreen and Smart App Control (SAC). However, recent findings by cybersecurity researchers have uncovered design weaknesses and potential attack vectors that could bypass these protective measures.
Impersonating Businesses and Exploiting EV Certificates
Attackers have been known to impersonate businesses and purchase Extended Validation (EV) signing certificates, which are difficult to steal. These certificates, while designed to enhance trust, can be exploited to make malicious software appear legitimate.
The LNK Stomping Bug and its Consequences
A bug in the handling of LNK files has been discovered, which can bypass Smart App Control and SmartScreen security controls. This bug, known as the LNK stomping bug, has been demonstrated in multiple samples on VirusTotal, indicating existing in-the-wild usage. The typical files previously used by financial criminals to exploit this bug were malicious LNK files.
Reputation Tampering and Hijacking
Reputation tampering is a third attack class against reputation systems, where some code sections could be modified without losing their associated reputation in Smart App Control. This method allows attackers to modify applications without triggering security alerts. Reputation hijacking is a generic attack paradigm on reputation-based malware protection systems, involving finding and repurposing apps with a good reputation to bypass the system.
Script hosts, such as Lua, Node.js, and AutoHotkey interpreters, are ideal targets for reputation hijacking attacks due to their foreign function interface (FFI) capability.
Bypassing Smart App Control and Mitigation Strategies
One way to bypass Smart App Control is to sign malware with a code-signing certificate. However, Microsoft exposes undocumented APIs for querying the trust level of files for SmartScreen and Smart App Control, which could potentially be used to mitigate this threat.
Elastic has developed a utility that displays the trust of a file and made the source code publicly available. The company has also disclosed details of the LNK stomping bug to the Microsoft Security Response Centre (MSRC).
The Importance of Vigilance and Multilayered Security
Smart App Control adds significant protection from new and emerging threats by blocking apps that are malicious or untrusted. However, it is essential to remember that no security system is foolproof, and security teams should scrutinise downloads carefully in their detection stack and not rely solely on OS-native security features for protection in this area.
In light of these findings, it is crucial for users to remain vigilant and adopt a multilayered security approach to ensure the safety of their systems and data.
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