t1505-002-transport-agent

name	T1505.002_transport-agent
description	Adversaries may abuse Microsoft transport agents to establish persistent access to systems.
category	configuration
version	18.1
author	cyberstrike-official
tags	["mitre-attack","enterprise","t1505.002","persistence","linux","windows","sub-technique"]
technique_id	T1505.002
tactic	persistence
all_tactics	["persistence"]
platforms	["Linux","Windows"]
mitre_url	https://attack.mitre.org/techniques/T1505/002
tech_stack	["linux","windows"]
cwe_ids	["CWE-276"]
chains_with	["T1505","T1505.001","T1505.003","T1505.004","T1505.005","T1505.006"]
prerequisites	["T1505"]
severity_boost	{"T1505":"Chain with T1505 for deeper attack path","T1505.001":"Chain with T1505.001 for deeper attack path","T1505.003":"Chain with T1505.003 for deeper attack path"}

T1505.002 Transport Agent

Sub-technique of: T1505

High-Level Description

Adversaries may abuse Microsoft transport agents to establish persistent access to systems. Microsoft Exchange transport agents can operate on email messages passing through the transport pipeline to perform various tasks such as filtering spam, filtering malicious attachments, journaling, or adding a corporate signature to the end of all outgoing emails. Transport agents can be written by application developers and then compiled to .NET assemblies that are subsequently registered with the Exchange server. Transport agents will be invoked during a specified stage of email processing and carry out developer defined tasks.

Adversaries may register a malicious transport agent to provide a persistence mechanism in Exchange Server that can be triggered by adversary-specified email events. Though a malicious transport agent may be invoked for all emails passing through the Exchange transport pipeline, the agent can be configured to only carry out specific tasks in response to adversary defined criteria. For example, the transport agent may only carry out an action like copying in-transit attachments and saving them for later exfiltration if the recipient email address matches an entry on a list provided by the adversary.

Kill Chain Phase

• Persistence (TA0003)

Platforms: Linux, Windows

What to Check

• Identify if Transport Agent technique is applicable to target environment
• Check Linux systems for indicators of Transport Agent
• Check Windows systems for indicators of Transport Agent
• Verify mitigations are bypassed or absent (3 known mitigations)
• Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Install MS Exchange Transport Agent Persistence

Install a Microsoft Exchange Transport Agent for persistence. This requires execution from an Exchange Client Access Server and the creation of a DLL with specific exports. Seen in use by Turla. More details- https://docs.microsoft.com/en-us/exchange/transport-agents-exchange-2013-help