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ATT&CK Technique

Space after Filename

T1036.006 · stealth

Adversaries can hide a program's true filetype by changing the extension of a file. With certain file types (specifically this does not work with .app extensions), appending a space to the end of a filename will change how the file is processed by the operating system. For example, if there is a Mach-O executable file called evil.bin, when it is double clicked by a user, it will launch Terminal.app and execute.

If this file is renamed to evil.txt, then when double clicked by a user, it will launch with the default text editing application (not executing the binary). However, if the file is renamed to evil.txt (note the space at the end), then when double clicked by a user, the true file type is determined by the OS and handled appropriately and the binary will be executed. Adversaries can use this feature to trick users into double clicking benign-looking files of any format and ultimately executing something malicious.

LinuxmacOS
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Actors Using This

1
north_koreaContagious Interview
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Atomic Tests

2
Executable Atomic Red Team test cases for exercising this technique in a lab. Copy a command, run it on the listed platform, confirm your detections fire.
manualmacosSpace After Filename (Manual)
Space After Filename
shmacos, linuxSpace After Filename
Space after filename. 
mkdir -p /tmp/atomic-test-T1036.006
cd /tmp/atomic-test-T1036.006
mkdir -p 'testdirwithspaceend '
[ "$(uname)" = 'FreeBSD' ] && /bin/echo "#\!/bin/sh" > "testdirwithspaceend /init " && echo 'echo "print(\"running T1035.006 with space after filename to masquerade init\")" | python3.9' >> "testdirwithspaceend /init " && echo "exit" >> "testdirwithspaceend /init " || /usr/bin/echo -e "%d\na\n#!/usr/bin/perl\nprint \"running T1035.006 with space after filename to masquerade init\\n\";\nqx/cp \/usr\/bin\/perl 'init  '/;\nqx/'.\/init  ' -e 'sleep 5'/;\n.\nwq\n" | ed 'testdirwithspaceend /init ' >/dev/null
chmod +x 'testdirwithspaceend /init '
'./testdirwithspaceend /init '
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Detection Coverage

1/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) 1
Analytics (MITRE CAR) none
Runtime / container (Falco) none
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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