Binary Padding
Binary Padding [T1027.001]
Last updated
Binary Padding [T1027.001]
Last updated
Name: Binary Padding
ID: T1027.001
Tactics:
Technique:
Binary Padding (T1027.001) is a sub-technique within the MITRE ATT&CK framework under the parent technique "Obfuscated Files or Information" (T1027). Attackers utilize binary padding to evade detection by adding superfluous data or null bytes to executables or binary files. This additional padding modifies the file's hash signature, making it challenging for security tools that rely on hash-based detection or file size heuristics to identify malicious binaries. Binary padding does not typically alter the functionality of the executable, but it can severely hinder signature-based detection methods.
Binary padding involves appending arbitrary data, commonly null bytes (0x00), random bytes, or repeating patterns, to the end or within the body of a binary file. Attackers perform this padding to alter the file's cryptographic hash without affecting the executable's functionality. Padding can be done using various tools and scripting languages, making it straightforward and accessible to threat actors.
Technical details and execution mechanisms include:
Appending Null Bytes:
Attackers append sequences of null bytes to the end of a binary file.
Null bytes do not affect program execution but change the file hash, bypassing signature-based detection.
Random Byte Padding:
Random data is appended or inserted within unused sections of a binary.
Random padding further complicates detection by creating unpredictably altered hashes.
Section Padding:
Attackers insert padding into unused or less critical file sections, such as the PE (Portable Executable) file format sections.
Padding can occur in sections like .data, .rsrc, or custom-created sections that do not affect the executable's functionality.
File Alignment Padding:
Files may be padded to align them to specific offsets or sizes, disguising malicious payloads in otherwise legitimate-looking files.
Real-world procedures often involve:
Using scripting languages (Python, PowerShell) or custom tools to automate padding processes.
Leveraging open-source tools or malware frameworks to quickly modify binaries and evade antivirus signatures.
Combining binary padding techniques with other obfuscation methods, such as packing or encryption, to further complicate detection.
Attackers typically employ binary padding in various scenarios and stages of cyber-attacks, including:
Initial Access and Delivery:
Malicious binaries delivered via spear-phishing attachments or links may be padded to avoid email gateway detection.
Padding helps attackers bypass perimeter defenses relying on hash-based or signature-based detection.
Execution and Persistence:
Malware executables placed on compromised systems may be padded to evade endpoint detection and response (EDR) solutions.
Attackers use padding to maintain persistence by periodically altering binaries to avoid detection over time.
Defense Evasion and Lateral Movement:
Attackers pad binaries used in lateral movement tools, such as Mimikatz or PsExec variants, to evade internal monitoring tools.
Padding is used to evade detection during post-compromise activities, ensuring stealthier lateral movement.
Command and Control (C2):
Malicious payloads delivered from C2 servers may use binary padding to bypass network-based detection systems that analyze file hashes or sizes.
Detection of binary padding typically involves multiple methods and tools, including:
Behavioral Analysis and Sandboxing:
Running executables in sandbox environments to detect malicious behaviors despite hash evasion.
Observing runtime behaviors helps detect padded binaries that evade static analysis.
Entropy and File Structure Analysis:
Analyzing file entropy to detect abnormal padding or randomness within binaries.
Tools such as PEStudio, Detect It Easy (DIE), and YARA rules can identify abnormal padding patterns.
Advanced Endpoint Detection and Response (EDR):
EDR solutions continuously monitor binary execution and file modifications, detecting suspicious files even when padded.
Detection of unusual file modifications or file size changes can trigger alerts.
File Integrity Monitoring (FIM):
Monitoring changes in file sizes or hashes can help detect padded binaries.
FIM solutions alert on unexpected file modifications, providing early indicators of compromise.
Static and Dynamic Analysis Tools:
Static analysis tools that detect unusual sections or appended data in PE files.
Dynamic analysis tools that monitor runtime behavior, identifying malicious activity despite padding.
Indicators of Compromise (IoCs) specific to binary padding include:
Unexpected file size increases or discrepancies.
High entropy sections appended to binaries.
Unusual padding bytes (null bytes, repetitive patterns) at the end of files.
Frequent file hash changes without corresponding functionality changes.
Detecting binary padding is crucial due to its potential impacts and threat implications:
Evasion of Traditional Detection Mechanisms:
Binary padding effectively bypasses hash-based detection methods, allowing malware to evade antivirus and endpoint protection systems.
Prolonged Persistence and Stealth:
Attackers using padded binaries can maintain persistent access undetected for extended periods, increasing potential damage and lateral movement opportunities.
Increased Difficulty of Incident Response:
Padded binaries complicate incident response and forensic analysis, making it harder to correlate malicious files across multiple compromised systems.
Potential for Malware Delivery and Execution:
Attackers leverage binary padding to successfully deliver and execute malicious payloads, leading to data theft, ransomware deployment, or espionage activities.
Reduced Security Posture and Increased Risk:
Failure to detect padded binaries can lead to prolonged attacker dwell time, enabling attackers to escalate privileges, exfiltrate sensitive data, or disrupt critical systems.
Early detection of binary padding techniques significantly reduces the risk of successful cyber-attacks, limits attacker dwell time, and strengthens overall organizational security posture.
Real-world examples and scenarios involving binary padding include:
APT29 (Cozy Bear):
Known to utilize binary padding to evade detection during initial access and lateral movement.
Padded binaries delivered via spear-phishing emails bypassed signature-based antivirus detection, enabling initial foothold establishment.
TrickBot Malware:
Frequently uses binary padding to evade endpoint detection solutions.
Attackers padded TrickBot binaries with null bytes or random data to alter hashes, enabling successful execution and persistence.
Emotet Malware Campaigns:
Emotet operators appended random data to binaries to avoid hash-based detection mechanisms.
Padded binaries were delivered via malicious email attachments, successfully evading email gateways and endpoint antivirus solutions.
Cobalt Strike Framework:
Attackers using Cobalt Strike payloads often pad binaries to evade static detection tools.
Binary padding combined with other obfuscation methods allowed attackers to establish command-and-control channels and maintain persistence undetected.
Custom Malware Used in Targeted Attacks:
Advanced persistent threats (APTs) frequently pad custom malware binaries to evade detection.
Padding techniques enabled attackers to maintain stealthy persistence within targeted organizations, facilitating data exfiltration and espionage activities.