MsBuild Making Network Connections

  1[metadata]
  2creation_date = "2020/02/18"
  3integration = ["endpoint"]
  4maturity = "production"
  5updated_date = "2025/03/20"
  6
  7[transform]
  8[[transform.osquery]]
  9label = "Osquery - Retrieve DNS Cache"
 10query = "SELECT * FROM dns_cache"
 11
 12[[transform.osquery]]
 13label = "Osquery - Retrieve All Services"
 14query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 15
 16[[transform.osquery]]
 17label = "Osquery - Retrieve Services Running on User Accounts"
 18query = """
 19SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 20NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 21user_account == null)
 22"""
 23
 24[[transform.osquery]]
 25label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 26query = """
 27SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 28services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 29authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 30"""
 31
 32
 33[rule]
 34author = ["Elastic"]
 35description = """
 36Identifies MsBuild.exe making outbound network connections. This may indicate adversarial activity as MsBuild is often
 37leveraged by adversaries to execute code and evade detection.
 38"""
 39from = "now-9m"
 40index = ["logs-endpoint.events.process-*", "logs-endpoint.events.network-*"]
 41language = "eql"
 42license = "Elastic License v2"
 43name = "MsBuild Making Network Connections"
 44note = """## Triage and analysis
 45
 46### Performance
 47
 48The 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.
 49
 50### Investigating MsBuild Making Network Connections
 51
 52By 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.
 53
 54The 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.
 55
 56This 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.
 57
 58> **Note**:
 59> 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.
 60
 61#### Possible investigation steps
 62
 63- Investigate other alerts associated with the user/host during the past 48 hours.
 64- 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.
 65  - Investigate any abnormal behavior by the subject process such as network connections, registry or file modifications, and any spawned child processes.
 66  - Investigate the file digital signature and process original filename, if suspicious, treat it as potential malware.
 67- Investigate the target host that the signed binary is communicating with.
 68  - Check if the domain is newly registered or unexpected.
 69  - Check the reputation of the domain or IP address.
 70- Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
 71- Examine the host for derived artifacts that indicate suspicious activities:
 72  - Analyze the process executable using a private sandboxed analysis system.
 73  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 74    - Attempts to contact external domains and addresses.
 75      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 76      - Examine the DNS cache for suspicious or anomalous entries.
 77        - $osquery_0
 78    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 79    - Examine the host services for suspicious or anomalous entries.
 80      - $osquery_1
 81      - $osquery_2
 82      - $osquery_3
 83  - 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.
 84
 85### False positive analysis
 86
 87- 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.
 88
 89### Response and remediation
 90
 91- Initiate the incident response process based on the outcome of the triage.
 92- Isolate the involved host to prevent further post-compromise behavior.
 93- If the triage identified malware, search the environment for additional compromised hosts.
 94  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 95  - Stop suspicious processes.
 96  - Immediately block the identified indicators of compromise (IoCs).
 97  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 98- Remove and block malicious artifacts identified during triage.
 99- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
100- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
101- 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).
102"""
103references = ["https://riccardoancarani.github.io/2019-10-19-hunting-covenant-msbuild/"]
104risk_score = 47
105rule_id = "0e79980b-4250-4a50-a509-69294c14e84b"
106severity = "medium"
107tags = [
108    "Domain: Endpoint",
109    "OS: Windows",
110    "Use Case: Threat Detection",
111    "Tactic: Defense Evasion",
112    "Resources: Investigation Guide",
113    "Data Source: Elastic Defend",
114]
115type = "eql"
116
117query = '''
118sequence by process.entity_id with maxspan=30s
119
120  /* Look for MSBuild.exe process execution */
121  /* The events for this first sequence may be noisy, consider adding exceptions */
122  [process where host.os.type == "windows" and event.type == "start" and
123    (
124      process.pe.original_file_name: "MSBuild.exe" or
125      process.name: "MSBuild.exe"
126    ) and
127    not user.id == "S-1-5-18"]
128
129  /* Followed by a network connection to an external address */
130  /* Exclude domains that are known to be benign */
131  [network where host.os.type == "windows" and
132    event.action: ("connection_attempted", "lookup_requested") and
133    (
134      process.pe.original_file_name: "MSBuild.exe" or
135      process.name: "MSBuild.exe"
136    ) and
137    not user.id == "S-1-5-18" and
138    not cidrmatch(destination.ip, "127.0.0.1", "::1") and
139    not dns.question.name : (
140      "localhost",
141      "dc.services.visualstudio.com",
142      "vortex.data.microsoft.com",
143      "api.nuget.org")]
144'''
145
146
147[[rule.threat]]
148framework = "MITRE ATT&CK"
149[[rule.threat.technique]]
150id = "T1127"
151name = "Trusted Developer Utilities Proxy Execution"
152reference = "https://attack.mitre.org/techniques/T1127/"
153[[rule.threat.technique.subtechnique]]
154id = "T1127.001"
155name = "MSBuild"
156reference = "https://attack.mitre.org/techniques/T1127/001/"
157
158
159
160[rule.threat.tactic]
161id = "TA0005"
162name = "Defense Evasion"
163reference = "https://attack.mitre.org/tactics/TA0005/"