>tee
Tee reads from standard input and writes to standard output and files. Attackers abuse SUID or sudo tee to append unauthorized credentials to /etc/passwd or overwrite system configuration.
Default Executable Paths
/usr/bin/teeIntegrity & Metadata
Appending a line with UID 0 (root) into /etc/passwd creates an immediate backdoor administrative account.
Monitor process creation of tee targeting sensitive system files like /etc/passwd, /etc/shadow, or /etc/sudoers.
Executive Summary & AI Quick Reference
tee is a native utility pre-installed on Linux systems. Threat actors and red teams abuse tee as a Living-off-the-Land Binary (LOLBin) to achieve Persistence without triggering traditional antivirus file-hash alerts. Legitimate system administrators use it for routine administration, making behavioral command-line telemetry essential for differentiation.
Weaponized Parameters & Proof-of-Concepts
Documented attack commands, parameter flags, and privilege prerequisites.
Appends an unauthorized administrative account directly into the local passwd file.
echo "backdoor:x:0:0::/root:/bin/bash" | tee -a /etc/passwdSIEM & EDR Detection Rules
Production telemetry rules configured for Microsoft Defender, Sigma, and Splunk.
Telemetry & SIEM Detection Suite (tee)
Validated against MITRE T1565.001, T1136.0011DeviceProcessEvents | where FileName =~ "tee" | where ProcessCommandLine has_any ("/etc/passwd", "/etc/shadow", "/etc/sudoers") | project Timestamp, DeviceName, AccountName, ProcessCommandLineMitigation, Hardening & Prevention
Recommended defensive controls to block or constrain tee abuse.
Audit and remove unnecessary SUID / SGID bits (`chmod u-s /path/to/$tee`) and restrict sudoers NOPASSWD execution grants.
Implement AppArmor or SELinux profiles restricting tee network socket creation and read access to sensitive user directories.
Deploy the KQL, Sigma, and Splunk detection queries below. Alert on anomalous child processes, web requests to unrated external IPs, or encoded payload strings.
Frequently Asked Questions (FAQ) • tee
Key operational questions and defensive answers about tee LOLBin tradecraft.
What is tee and why is it classified as a LOLBin?
tee is a legitimate, pre-installed or trusted utility on Linux. It is classified as a Living-off-the-Land Binary (LOLBin) because adversaries abuse its built-in functionality to perform malicious operations—such as Persistence—without dropping custom malware binaries on disk.
How do threat actors abuse tee in cyber intrusions?
Adversaries leverage tee to execute stealthy actions while evading signature-based security controls. For example, attackers execute commands like "echo "backdoor:x:0:0::/root:/bin/bash" | tee -a /etc/passwd" to achieve Persistence, masquerading behind legitimate system process lineage.
How can SOC analysts detect suspicious tee activity?
Detection engineers monitor process creation events (Windows Event ID 4688 or Sysmon Event ID 1; Linux auditd EXECVE; macOS Endpoint Security) inspecting anomalous command line arguments, unusual parent-child process relationships (e.g. Office apps or web servers spawning tee), and unexpected network connections.
What MITRE ATT&CK techniques does tee map to?
tee maps to MITRE ATT&CK technique(s): T1565.001, T1136.001. These techniques cover adversary actions across tactics such as Defense Evasion, Execution, Persistence, and Command and Control.
How can organizations mitigate and restrict tee?
Mitigation strategies include implementing Application Control policies (AppLocker or Windows Defender Application Control - WDAC), enforcing Attack Surface Reduction (ASR) rules, configuring strict privilege separation (disallowing standard users from running sensitive switches), and alerting on execution from non-standard directories.
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