Detect Compromise Host Software Binary in CrowdStrike LogScale
Adversaries may modify host software binaries to establish persistent access to systems. Common targets include SSH clients/servers, FTP clients, web browsers, VPN daemons, and other frequently-executed system utilities. Attackers may replace a legitimate binary entirely with a trojanized version containing credential harvesting or backdoor functionality, or patch an existing binary at its entry point to redirect execution to malicious code before resuming normal operation. After modification, adversaries may use version-lock mechanisms (e.g., yum-versionlock, apt-mark hold) to prevent legitimate updates from overwriting the trojanized binary.
MITRE ATT&CK
- Tactic
- Persistence
- Technique
- T1554 Compromise Host Software Binary
- Canonical reference
- https://attack.mitre.org/techniques/T1554/
LogScale Detection Query
// Arm 1: Critical Binary File Write Events from Non-Updater Processes
#event_simpleName = "FileOpenInfo" OR #event_simpleName = "PeFileWritten"
| TargetFileName = /(?i)(\\Windows\\System32\\|\\Windows\\SysWOW64\\|\\Program Files\\OpenSSH\\|\\Program Files.*\\bin\\)/
| TargetFileName = /(?i)(ssh\.exe|sshd\.exe|sftp\.exe|curl\.exe|wget\.exe|putty\.exe|winscp\.exe|filezilla\.exe|chrome\.exe|firefox\.exe|msedge\.exe|iexplore\.exe|notepad\.exe|cmd\.exe|powershell\.exe|pwsh\.exe|taskmgr\.exe|regedit\.exe|mstsc\.exe|lsass\.exe)/
| ImageFileName != /(?i)(msiexec\.exe|TrustedInstaller\.exe|wusa\.exe|setup\.exe|install\.exe|WindowsUpdate|svchost\.exe)/
| case {
TargetFileName = /\.exe$/i => AlertReason := "WindowsSystemBinaryModification";
* => AlertReason := "SystemBinaryModification"
}
| table([_time, ComputerName, UserName, TargetFileName, ImageFileName, CommandLine, ParentBaseFileName, ParentCommandLine, AlertReason, SHA256HashData, MD5HashData])
| sort(field=_time, order=desc)
// Arm 2: Version-Lock Commands (run as separate hunt query)
// #event_simpleName = "ProcessRollup2"
// | CommandLine = /(?i)(versionlock|yum-versionlock|apt-mark\s+hold|dpkg\s+--set-selections|apt-mark\s+unhold)/
// | eval AlertReason := "VersionLockDetected"
// | table([_time, ComputerName, UserName, FileName, CommandLine, ParentBaseFileName, ParentCommandLine, AlertReason])
// | sort(field=_time, order=desc)CrowdStrike LogScale (CQL) detection for T1554 host software binary compromise. Arm 1 uses PeFileWritten and FileOpenInfo events to detect PE binary writes to critical Windows system directories from non-trusted processes. Arm 2 (commented for separate use) detects version-lock commands via ProcessRollup2 events. Both arms should be combined in a dashboard for full coverage.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike Falcon sensor updates that write sensor components to system paths — the sensor process itself may appear as a non-standard updater triggering this detection
- Software vendors that bundle their own copies of curl.exe, wget.exe, or ssh.exe in Program Files subdirectories and update them via proprietary installer processes not matching the exclusion list
- System administrators using Chocolatey, Scoop, or winget package managers which may write binaries to system directories under PowerShell or cmd.exe parent processes rather than TrustedInstaller
Other platforms for T1554
Testing Methodology
Validate this detection against 5 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 1Replace System Binary with Modified Copy (Windows)
Expected signal: Sysmon Event ID 11: FileCreate targeting C:\Windows\System32\notepad.exe with Image=powershell.exe. Sysmon Event ID 2: FileCreateTime change for notepad.exe if timestamps diverge. DeviceFileEvents ActionType=FileModified with FileName=notepad.exe in SystemBinaryPaths, InitiatingProcessFileName=powershell.exe. SHA256 will not match Microsoft-published hash.
- Test 2Hash Verification and Signature Check Workflow (Windows)
Expected signal: DeviceProcessEvents: powershell.exe executing Get-FileHash and Get-AuthenticodeSignature. No file modification events — this is read-only. Output provides hashes for comparison against Microsoft Security Response Center published values or NSRL hash database.
- Test 3Trojanize SSH Client Binary (Linux)
Expected signal: auditd: SYSCALL record for open(O_WRONLY) on /usr/bin/ssh by root/sudo, comm=cp. Linux syslog: sudo invocation logs showing binary replacement. 'rpm -V openssh-clients' reports 'S.5......' (size and hash mismatch). If MDE Linux agent deployed: DeviceFileEvents ActionType=FileModified for /usr/bin/ssh. After execution, /tmp/.t1554_harvest.log created (Sysmon Event ID 11 equivalent on Linux).
- Test 4Version Lock Compromised Package (Linux — UNC3886 TTP)
Expected signal: Linux syslog/secure: sudo execution of 'yum versionlock openssh-clients' or 'apt-mark hold openssh-client' with effective UID=0. DeviceProcessEvents (MDE Linux): ProcessCommandLine containing 'versionlock' or 'apt-mark hold', AccountName=root or sudo-invoked user. Auditd: EXECVE record for yum/apt-mark with full argument list.
- Test 5Browser Binary Replacement Simulation (macOS — XCSSET TTP)
Expected signal: macOS Unified Log: ES_EVENT_TYPE_NOTIFY_WRITE for /Applications/Firefox.app/Contents/MacOS/firefox from sudo/bash. macOS Gatekeeper: 'codesign --verify /Applications/Firefox.app' reports code signature invalid. If MDE macOS agent deployed: DeviceFileEvents ActionType=FileModified for browser binary path with initiating process=bash/sudo. macOS LaunchServices quarantine: application launch may trigger Gatekeeper alert when modified app is opened.
References (10)
- https://attack.mitre.org/techniques/T1554/
- https://cloud.google.com/blog/topics/threat-intelligence/uncovering-unc3886-espionage-operations
- https://www.welivesecurity.com/2021/01/26/kobalos-complex-linux-threat-high-performance-computing-infrastructure/
- https://www.welivesecurity.com/2014/02/21/an-in-depth-analysis-of-linuxebury/
- https://www.mandiant.com/resources/blog/cutting-edge-suspected-apt-targets-ivanti-connect-secure-vpn-zero-day-exploits
- https://web-assets.esetstatic.com/wls/2021/10/eset_fontonlake.pdf
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1554/T1554.md
- https://learn.microsoft.com/en-us/sysinternals/downloads/sigcheck
- https://man7.org/linux/man-pages/man8/auditd.8.html
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-devicefileevents-table
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