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ATT&CK Technique

Binary Padding

T1027.001 · stealth

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.

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. 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.

LinuxmacOSWindows
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Actors Using This

14
iranAgrius
franceAnimal Farm
russiaAPT29
chinaAPT31
north_koreaAPT37
north_koreaAPT38
chinaAPT40
brazilBanbra
russia_speaking_organized_cybercrimeBumblebee Operators / EXOTIC LILY
israel_commercial_cyber_mercenaryCandiru / Sourgum
spainCareto / The Mask
north_koreaCitrine Sleet
north_koreaContagious Interview
chinaCosmicStrand
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Likely Attack Path

Techniques the same actors pair with this one distinctively - those showing up among actors who use this technique noticeably more than across all actors (lift > 1.15), grouped by kill-chain phase. The × is that lift multiplier; the shared-actor count is in the tooltip. A near-universal technique pairs with everything at baseline, so its list is short by design.
resource-development same
T1608.004 · Drive-by Target ×3.36T1608.005 · Link Target ×3.25T1586.001 · Social Media Accounts ×2.88T1608.001 · Upload Malware ×2.80T1586.002 · Email Accounts ×2.42
initial-access same
T1195.001 · Compromise Software Dependencies and Development Tools ×2.40
execution same
T1559.001 · Component Object Model ×2.62
privilege-escalation same
T1548.002 · Bypass User Account Control ×2.69T1134.001 · Token Impersonation/Theft ×2.56
credential-access same
T1558 · Steal or Forge Kerberos Tickets ×2.88
discovery same
T1012 · Query Registry ×2.42
lateral-movement same
T1550.003 · Pass the Ticket ×2.88
collection same
T1602 · Data from Configuration Repository ×3.20
exfiltration same
T1048.002 · Exfiltration Over Asymmetric Encrypted Non-C2 Protocol ×2.56
other same
T1562.002 · Disable Windows Event Logging ×2.56
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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.
shlinux, macosPad 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 `/tmp/evil-binary`, therefore the expected hash will change. 
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
shlinux, macosPad 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 `/tmp/evil-binary`, therefore the expected hash will change. 
truncate -s +1 #{file_to_pad} #adds a byte to the file size
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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) 3
Analytics (MITRE CAR) none
Runtime / container (Falco) none
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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Comply & Defend

D3FEND12 defensive techniques
Intelligence Graph · click any node to traverse
CVETechnique ActorTool Family
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External lookups - second-class, for what we don’t hold ourselves
MITRE ATT&CKAtomic Red Teamcar (MITRE)
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