T1036.006 Space after Filename

> Sub-technique of: T1036

High-Level Description

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 <code>evil.bin</code>, when it is double clicked by a user, it will launch Terminal.app and execute. If this file is renamed to <code>evil.txt</code>, 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 <code>evil.txt </code> (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.

Kill Chain Phase

• Defense Evasion (TA0005)

Platforms: Linux, macOS

What to Check

• ] Identify if Space after Filename technique is applicable to target environment
• ] Check Linux systems for indicators of Space after Filename
• ] Check macOS systems for indicators of Space after Filename
• ] Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Space After Filename (Manual)

Space After Filename

Supported Platforms: macos

Atomic Test 2: Space After Filename

Space after filename.

Supported Platforms: macos, linux

bash
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 '

Manual Testing

If Atomic Red Team tests are not applicable, manually verify the technique by:

1. Identify Attack Surface: Determine if the target environment is susceptible to Space after Filename by examining the target platforms (Linux, macOS).

1. Assess Existing Defenses: Review whether mitigations for T1036.006 are in place. If defenses are absent or misconfigured, this technique may be exploitable.

1. Execute Test: Use tools and methods described in the MITRE ATT&CK page and external references below.

Remediation Guide

No specific mitigations documented for this technique.

Detection

Masquerading via Space After Filename - Behavioral Detection Strategy

Risk Assessment

| Finding | Severity | Impact | | ----------------------------------------- | -------- | --------------- | | Space after Filename technique applicable | High | Defense Evasion |

CWE Categories

| CWE ID | Title | | ------- | ---------------------------- | | CWE-693 | Protection Mechanism Failure |

References

• Mac Backdoors are back
• Atomic Red Team - T1036.006
• MITRE ATT&CK - T1036.006