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ATT&CK Technique

Port Monitors

T1547.010 · persistence, privilege-escalation

Adversaries may use port monitors to run an adversary supplied DLL during system boot for persistence or privilege escalation. A port monitor can be set through the AddMonitor API call to set a DLL to be loaded at startup. This DLL can be located in C:\Windows\System32 and will be loaded and run by the print spooler service, spoolsv.exe, under SYSTEM level permissions on boot.

Alternatively, an arbitrary DLL can be loaded if permissions allow writing a fully-qualified pathname for that DLL to the Driver value of an existing or new arbitrarily named subkey of HKLM\SYSTEM\CurrentControlSet\Control\Print\Monitors. The Registry key contains entries for the following: Local Port Standard TCP/IP Port USB Monitor WSD Port.

Windows
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Atomic Tests

1
Executable Atomic Red Team test cases for exercising this technique in a lab. Copy a command, run it on the listed platform, confirm your detections fire.
command_promptelevatedwindowsAdd Port Monitor persistence in Registry
Add key-value pair to a Windows Port Monitor registry. On the subsequent reboot DLL will be execute under spoolsv with NT AUTHORITY/SYSTEM privilege.
reg add "hklm\system\currentcontrolset\control\print\monitors\AtomicRedTeam" /v "Driver" /d "#{monitor_dll}" /t REG_SZ /f
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Detection Coverage

2/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) 4
Analytics (MITRE CAR) 1
Runtime / container (Falco) none
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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CAR Analytics

1
MITRE Cyber Analytics Repository - field-tested detection logic for this technique, written as pseudocode/queries you adapt to your own SIEM (Splunk, Sentinel, EQL). Each is a ready starting point for a detection rule, not just a description.
CAR-2013-01-002Moderate coverageAutorun Differences

The Sysinternals tool [Autoruns](../sensors/autoruns) checks the registry and file system for known identify persistence mechanisms. It will output any tools identified, including built-in or added-on Microsoft functionality and third party software. Many of these locations are known by adversaries and used to obtain Persistence.

Running Autoruns periodically in an environment makes it possible to collect and monitor its output for differences, which may include the removal or addition of persistent tools. Depending on the persistence mechanism and location, legitimate software may be more likely to make changes than an adversary tool. Thus, this analytic may result in significant noise in a highly dynamic environment.

While Autoruns is a convenient method to scan for programs using persistence mechanisms its scanning nature does not conform well to streaming based analytics. This analytic could be replaced with one that draws from sensors that collect registry and file information if streaming analytics are desired. Utilizes the Sysinternals autoruns tool (ignoring validated Microsoft entries).

Primarily not a detection analytic by itself but through analysis of results by an analyst can be used for such. Building another analytic on top of this one identifying unusual entries would likely be a beneficial alternative.

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