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New 'Illusion Gap' Attack Bypasses Windows Defender Scans (bleepingcomputer.com)
An anonymous reader writes: Security researchers have discovered a new technique that allows malware to bypass Windows Defender, the standard security software that comes included with all Windows operating systems. The technique -- nicknamed Illusion Gap -- relies on a mixture of both social engineering and the use of a rogue SMB server.
The attack exploits a design choice in how Windows Defender scans files stored on an SMB share before execution. For Illusion Gap to work, the attacker must convince a user to execute a file hosted on a malicious SMB server under his control. This is not as complex as it sounds, as a simple shortcut file is all that's needed.
The problems occur after the user double-clicks this malicious file. By default, Windows will request from the SMB server a copy of the file for the task of creating the process that executes the file, while Windows Defender will request a copy of the file in order to scan it. SMB servers can distinguish between these two requests, and this is a problem because an attacker can configure their malicious SMB server to respond with two different files. The attacker can send a malicious file to the Windows PE Loader, and a benign file to Windows Defender. After Windows Defender scans the clean file and gives the go-ahead, Windows PE Loader will execute the malicious file without Windows Defender realizing they're two different things. Microsoft declined to patch the bug, considering it a "feature request."
The attack exploits a design choice in how Windows Defender scans files stored on an SMB share before execution. For Illusion Gap to work, the attacker must convince a user to execute a file hosted on a malicious SMB server under his control. This is not as complex as it sounds, as a simple shortcut file is all that's needed.
The problems occur after the user double-clicks this malicious file. By default, Windows will request from the SMB server a copy of the file for the task of creating the process that executes the file, while Windows Defender will request a copy of the file in order to scan it. SMB servers can distinguish between these two requests, and this is a problem because an attacker can configure their malicious SMB server to respond with two different files. The attacker can send a malicious file to the Windows PE Loader, and a benign file to Windows Defender. After Windows Defender scans the clean file and gives the go-ahead, Windows PE Loader will execute the malicious file without Windows Defender realizing they're two different things. Microsoft declined to patch the bug, considering it a "feature request."
Windows does have an equivalent of ptrace, so how exactly is this a problem? You hook onto the process that's being created (on Windows there's no separation between fork and exec) having it start as traced. It gets mmapped, you check whatever got loaded into that process' address space, detach the trace.
It'd also have double the performance when the file fits into memory: no need to request the file over network twice. And if it doesn't fit, well, page cache is perfectly equipped to deal with this.
The creatures outside looked from Alt-Right to Antifa; but already it was impossible to say which was which.