MsBuild Making Network Connections

  1[metadata]
  2creation_date = "2020/02/18"
  3integration = ["endpoint"]
  4maturity = "production"
  5updated_date = "2026/09/18"
  6[transform]
  7[[transform.osquery]]
  8label = "Osquery - Retrieve DNS Cache"
  9query = "SELECT * FROM dns_cache"
 10
 11[[transform.osquery]]
 12label = "Osquery - Retrieve All Services"
 13query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 14
 15[[transform.osquery]]
 16label = "Osquery - Retrieve Services Running on User Accounts"
 17query = """
 18SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 19NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 20user_account == null)
 21"""
 22
 23[[transform.osquery]]
 24label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 25query = """
 26SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 27services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 28authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 29"""
 30
 31
 32[rule]
 33author = ["Elastic"]
 34description = """
 35Identifies MsBuild.exe making outbound network connections. This may indicate adversarial activity as MsBuild is often
 36leveraged by adversaries to execute code and evade detection.
 37"""
 38from = "now-9m"
 39index = ["logs-endpoint.events.process-*", "logs-endpoint.events.network-*"]
 40language = "eql"
 41license = "Elastic License v2"
 42name = "MsBuild Making Network Connections"
 43note = """## Triage and analysis
 44
 45### Performance
 46
 47The performance impact of this rule is expected to be low to medium because of the first sequence, which looks for MsBuild.exe process execution. The events for this first sequence may be noisy, consider adding exceptions.
 48
 49### Investigating MsBuild Making Network Connections
 50
 51By examining the specific traits of Windows binaries (such as process trees, command lines, network connections, registry modifications, and so on) it's possible to establish a baseline of normal activity. Deviations from this baseline can indicate malicious activity, such as masquerading and deserve further investigation.
 52
 53The Microsoft Build Engine, also known as MSBuild, is a platform for building applications. This engine provides an XML schema for a project file that controls how the build platform processes and builds software, and can be abused to proxy code execution.
 54
 55This rule looks for the `Msbuild.exe` utility execution, followed by a network connection to an external address. Attackers can abuse MsBuild to execute malicious files or masquerade as those utilities in order to bypass detections and evade defenses.
 56
 57> **Note**:
 58> This investigation guide uses the [Osquery Markdown Plugin](https://www.elastic.co/guide/en/security/current/invest-guide-run-osquery.html) introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display unrendered Markdown in this guide.
 59
 60#### Possible investigation steps
 61
 62- Investigate other alerts associated with the user/host during the past 48 hours.
 63- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
 64  - Investigate any abnormal behavior by the subject process such as network connections, registry or file modifications, and any spawned child processes.
 65  - Investigate the file digital signature and process original filename, if suspicious, treat it as potential malware.
 66- Investigate the target host that the signed binary is communicating with.
 67  - Check if the domain is newly registered or unexpected.
 68  - Check the reputation of the domain or IP address.
 69- Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
 70- Examine the host for derived artifacts that indicate suspicious activities:
 71  - Analyze the process executable using a private sandboxed analysis system.
 72  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 73    - Attempts to contact external domains and addresses.
 74      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 75      - Examine the DNS cache for suspicious or anomalous entries.
 76        - $osquery_0
 77    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 78    - Examine the host services for suspicious or anomalous entries.
 79      - $osquery_1
 80      - $osquery_2
 81      - $osquery_3
 82  - Retrieve the files' SHA-256 hash values using the PowerShell `Get-FileHash` cmdlet and search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 83
 84### False positive analysis
 85
 86- If this activity is expected and noisy in your environment, consider adding exceptions — preferably with a combination of destination IP address and command line conditions.
 87
 88### Response and remediation
 89
 90- Initiate the incident response process based on the outcome of the triage.
 91- Isolate the involved host to prevent further post-compromise behavior.
 92- If the triage identified malware, search the environment for additional compromised hosts.
 93  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 94  - Stop suspicious processes.
 95  - Immediately block the identified indicators of compromise (IoCs).
 96  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 97- Remove and block malicious artifacts identified during triage.
 98- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 99- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
100- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the mean time to respond (MTTR).
101"""
102
103setup = """## Setup
104
105This rule is designed for data generated by [Elastic Defend](https://www.elastic.co/security/endpoint-security), which provides native endpoint detection and response, along with event enrichments designed to work with our detection rules.
106
107Setup instructions: https://ela.st/install-elastic-defend
108"""
109
110references = ["https://riccardoancarani.github.io/2019-10-19-hunting-covenant-msbuild/"]
111risk_score = 47
112rule_id = "0e79980b-4250-4a50-a509-69294c14e84b"
113severity = "medium"
114tags = [
115    "Domain: Endpoint",
116    "OS: Windows",
117    "Use Case: Threat Detection",
118    "Tactic: Defense Evasion",
119    "Resources: Investigation Guide",
120    "Data Source: Elastic Defend",
121    "Noise: Medium",
122    "Performance: Normal",
123    "Rule Type: Event Correlation (EQL)",
124    "Platform: Windows",
125    "Resources: Osquery",
126]
127type = "eql"
128
129query = '''
130sequence by process.entity_id with maxspan=30s
131
132  /* Look for MSBuild.exe process execution */
133  /* The events for this first sequence may be noisy, consider adding exceptions */
134  [process where host.os.type == "windows" and event.type == "start" and
135    (
136      process.pe.original_file_name: "MSBuild.exe" or
137      process.name: "MSBuild.exe"
138    ) and
139    not user.id == "S-1-5-18"]
140
141  /* Followed by a network connection to an external address */
142  /* Exclude domains that are known to be benign */
143  [network where host.os.type == "windows" and
144    event.action: ("connection_attempted", "lookup_requested") and
145    not user.id == "S-1-5-18" and
146    not cidrmatch(destination.ip, "127.0.0.1", "::1") and
147    not dns.question.name : (
148      "localhost",
149      "dc.services.visualstudio.com",
150      "vortex.data.microsoft.com",
151      "api.nuget.org")]
152'''
153
154
155[[rule.threat]]
156framework = "MITRE ATT&CK"
157
158[[rule.threat.technique]]
159id = "T1127"
160name = "Trusted Developer Utilities Proxy Execution"
161reference = "https://attack.mitre.org/techniques/T1127/"
162
163[[rule.threat.technique.subtechnique]]
164id = "T1127.001"
165name = "MSBuild"
166reference = "https://attack.mitre.org/techniques/T1127/001/"
167
168[rule.threat.tactic]
169id = "TA0005"
170name = "Defense Evasion"
171reference = "https://attack.mitre.org/tactics/TA0005/"
172
173[[rule.threat]]
174framework = "MITRE ATT&CK"
175
176[[rule.threat.technique]]
177id = "T1071"
178name = "Application Layer Protocol"
179reference = "https://attack.mitre.org/techniques/T1071/"
180
181[rule.threat.tactic]
182id = "TA0011"
183name = "Command and Control"
184reference = "https://attack.mitre.org/tactics/TA0011/"