>less
Less is an interactive terminal file pager. When invoked via sudo without secure mode, operators can escape to an interactive shell by issuing !/bin/sh from within the viewer.
Default Executable Paths
/usr/bin/less/bin/lessIntegrity & Metadata
If LESSSECURE environment variable is not set, less permits unrestricted external command execution.
Monitor for shell processes (/bin/sh, /bin/bash) whose parent process is less.
Executive Summary & AI Quick Reference
less is a native utility pre-installed on Linux systems. Threat actors and red teams abuse less as a Living-off-the-Land Binary (LOLBin) to achieve Execute 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.
Open file in less pager, then type !/bin/sh and press Enter to spawn a privileged shell.
less /etc/hostsSIEM & EDR Detection Rules
Production telemetry rules configured for Microsoft Defender, Sigma, and Splunk.
Telemetry & SIEM Detection Suite (less)
Validated against MITRE T1059.0041DeviceProcessEvents | where InitiatingProcessFileName =~ "less" and FileName in~ ("sh", "bash", "dash", "zsh") | project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, FileName, ProcessCommandLineMitigation, Hardening & Prevention
Recommended defensive controls to block or constrain less abuse.
Audit and remove unnecessary SUID / SGID bits (`chmod u-s /path/to/$less`) and restrict sudoers NOPASSWD execution grants.
Implement AppArmor or SELinux profiles restricting less 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) • less
Key operational questions and defensive answers about less LOLBin tradecraft.
What is less and why is it classified as a LOLBin?
less 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 Execute—without dropping custom malware binaries on disk.
How do threat actors abuse less in cyber intrusions?
Adversaries leverage less to execute stealthy actions while evading signature-based security controls. For example, attackers execute commands like "less /etc/hosts" to achieve Execute, masquerading behind legitimate system process lineage.
How can SOC analysts detect suspicious less 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 less), and unexpected network connections.
What MITRE ATT&CK techniques does less map to?
less maps to MITRE ATT&CK technique(s): T1059.004. These techniques cover adversary actions across tactics such as Defense Evasion, Execution, Persistence, and Command and Control.
How can organizations mitigate and restrict less?
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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