T1027.001
Obfuscated Files or Information: Binary Padding
Description from ATT&CK
Adversaries may use binary padding to add junk data and change the on-disk representation of malware. This can be done without affecting the functionality or behavior of a binary, but can increase the size of the binary beyond what some security tools are capable of handling due to file size limitations.
Binary padding effectively changes the checksum of the file and can also be used to avoid hash-based blocklists and static anti-virus signatures.(Citation: ESET OceanLotus) The padding used is commonly generated by a function to create junk data and then appended to the end or applied to sections of malware.(Citation: Securelist Malware Tricks April 2017) Increasing the file size may decrease the effectiveness of certain tools and detection capabilities that are not designed or configured to scan large files. This may also reduce the likelihood of being collected for analysis. Public file scanning services, such as VirusTotal, limits the maximum size of an uploaded file to be analyzed.(Citation: VirusTotal FAQ)
Atomic Tests
Atomic Test #1 - Pad Binary to Change Hash - Linux/macOS dd
Uses dd to add a zero byte, high-quality random data, and low-quality random data to the binary to change the hash.
Upon successful execution, dd will modify 1
/tmp/evil-binary
Supported Platforms: freebsd,macos,linux
auto_generated_guid: ffe2346c-abd5-4b45-a713-bf5f1ebd573a
Inputs:
| Name | Description | Type | Default Value |
|---|---|---|---|
| file_to_pad | Path of binary to be padded | path | /tmp/evil-binary |
Attack Commands: Run with sh!
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dd if=/dev/zero bs=1 count=1 >> #{file_to_pad} #adds null bytes
dd if=/dev/random bs=1 count=1 >> #{file_to_pad} #adds high-quality random data
dd if=/dev/urandom bs=1 count=1 >> #{file_to_pad} #adds low-quality random data
Cleanup Commands:
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rm #{file_to_pad}
Dependencies: Run with sh!
Description: The binary must exist on disk at specified location (#{file_to_pad})
Check Prereq Commands:
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if [ -f #{file_to_pad} ]; then exit 0; else exit 1; fi;
Get Prereq Commands:
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cp /bin/ls #{file_to_pad}
Atomic Test #2 - Pad Binary to Change Hash using truncate command - Linux/macOS
Uses truncate to add a byte to the binary to change the hash.
Upon successful execution, truncate will modify 1
/tmp/evil-binary
Supported Platforms: freebsd,macos,linux
auto_generated_guid: e22a9e89-69c7-410f-a473-e6c212cd2292
Inputs:
| Name | Description | Type | Default Value |
|---|---|---|---|
| file_to_pad | Path of binary to be padded | path | /tmp/evil-binary |
Attack Commands: Run with sh!
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truncate -s +1 #{file_to_pad} #adds a byte to the file size
Cleanup Commands:
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rm #{file_to_pad}
Dependencies: Run with sh!
Description: The binary must exist on disk at specified location (#{file_to_pad})
Check Prereq Commands:
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if [ -f #{file_to_pad} ]; then exit 0; else exit 1; fi;
Get Prereq Commands:
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cp /bin/ls #{file_to_pad}