Detect Binary Padding in IBM QRadar
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. Known threat actors including APT29, Kimsuky, Emotet, QakBot, Black Basta, and Akira have employed this technique to inflate file sizes and change file hashes.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1027 Obfuscated Files or Information
- Sub-technique
- T1027.001 Binary Padding
- Canonical reference
- https://attack.mitre.org/techniques/T1027/001/
QRadar Detection Query
SELECT
DATEFORMAT(devicetime, 'yyyy-MM-dd HH:mm:ss') AS EventTime,
LOGSOURCENAME(logsourceid) AS LogSource,
username AS UserName,
"TargetFilename",
LONG("FileSize") AS FileSizeBytes,
LONG("FileSize") / 1048576 AS FileSizeMB,
"Image" AS WritingProcess,
"CommandLine",
"Hashes"
FROM events
WHERE LOGSOURCETYPENAME(devicetype) ILIKE '%Sysmon%'
AND QIDNAME(qid) ILIKE '%File Create%'
AND (
"TargetFilename" ILIKE '%.exe'
OR "TargetFilename" ILIKE '%.dll'
OR "TargetFilename" ILIKE '%.sys'
)
AND LONG("FileSize") > 52428800
AND "TargetFilename" NOT ILIKE 'C:\\Windows\\%'
AND "TargetFilename" NOT ILIKE 'C:\\Program Files\\%'
AND "TargetFilename" NOT ILIKE 'C:\\Program Files (x86)\\%'
AND devicetime > DATEADD('hour', -24, NOW())
ORDER BY FileSizeBytes DESC
LIMIT 500Detects oversized PE file creation (>50MB) via Sysmon EventCode 11 (FileCreate) in IBM QRadar AQL. Queries the events table scoped to Sysmon log sources, filtering for .exe/.dll/.sys files exceeding 50MB outside trusted system directories. Uses LONG() casting for reliable numeric comparison of the FileSize custom property extracted by the Sysmon DSM. Binary padding (T1027.001) is used by threat actors to change file hashes and evade file-size-limited AV scanners.
Data Sources
Required Tables
False Positives & Tuning
- Enterprise patch management solutions (SCCM, Ivanti) writing large application update binaries to local staging directories before moving them to final installation paths under Program Files
- Software developers building large debug-mode executables with embedded PDB symbols and statically linked runtime libraries, writing output to project build directories outside system paths
- Security research or malware analysis environments where large benign test samples are written to sandboxed analysis directories by orchestration tooling
Other platforms for T1027.001
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Inflate Executable with Null Bytes using fsutil
Expected signal: Sysmon Event ID 11: File Create for padded_calc.exe in %TEMP%. Sysmon Event ID 1: Process Create for fsutil.exe with 'file seteof' command. Security Event ID 4688 (if enabled): fsutil.exe execution. The file hash of padded_calc.exe will differ from the original calc.exe hash.
- Test 2Append Random Bytes to Binary Using PowerShell
Expected signal: Sysmon Event ID 11: File Create for padded_notepad.exe. PowerShell Script Block Logging Event ID 4104 with the Add-Content and RandomNumberGenerator commands. The file will be approximately original size + 10MB.
- Test 3Binary Padding with DD Command on Linux
Expected signal: Syslog/auditd: execve syscall for cp and dd commands with their arguments. File creation event for /tmp/padded_ls. The file will be approximately 20MB larger than the original /bin/ls. The SHA256 hash will differ from the original.
- Test 4Verify Hash Change After Padding
Expected signal: Sysmon Event ID 1: certutil.exe process creation with '-hashfile' argument (twice). Sysmon Event ID 11: File modification of test_calc.exe. The two certutil executions will produce different SHA256 hashes, demonstrating the hash change.
References (6)
- https://attack.mitre.org/techniques/T1027/001/
- https://www.welivesecurity.com/2018/03/13/oceanlotus-ships-new-backdoor/
- https://securelist.com/old-malware-tricks-to-bypass-detection-in-the-age-of-big-data/78010/
- https://www.virustotal.com/en/faq/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1027.001/T1027.001.md
- https://www.mandiant.com/resources/blog/golang-internals-symbol-recovery
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