Rare Connection to WebDAV Target

  1[metadata]
  2creation_date = "2025/04/28"
  3integration = ["endpoint", "system", "windows", "m365_defender", "crowdstrike"]
  4maturity = "production"
  5updated_date = "2026/08/18"
  6
  7[rule]
  8author = ["Elastic"]
  9description = """
 10Identifies rare connection attempts to a Web Distributed Authoring and Versioning (WebDAV) resource. Attackers may
 11inject WebDAV paths in files or features opened by a victim user to leak their NTLM credentials via forced
 12authentication.
 13"""
 14from = "now-8h"
 15interval="1h"
 16language = "esql"
 17license = "Elastic License v2"
 18name = "Rare Connection to WebDAV Target"
 19note = """## Triage and analysis
 20
 21### Investigating Rare Connection to WebDAV Target
 22
 23### Possible investigation steps
 24
 25- Examine the reputation of the destination domain or IP address.
 26- Verify if the target user opened any attachments or clicked links pointing to the same target within seconds from the alert timestamp.
 27- Correlate the findings with other security logs and alerts to identify any patterns or additional indicators of compromise related to the potential relay attack.
 28
 29### False positive analysis
 30
 31- User accessing legit WebDAV resources.
 32
 33### Response and remediation
 34
 35- Conduct a password reset for the target account that may have been compromised or are at risk, ensuring the use of strong, unique passwords.
 36- Verify whether other users were targeted but did not open the lure..
 37- Escalate the incident to the security operations center (SOC) or incident response team for further investigation and to determine the full scope of the breach.
 38- Conduct a post-incident review to identify any gaps in security controls and update policies or procedures to prevent recurrence, ensuring lessons learned are applied to improve overall security posture."""
 39references = ["https://attack.mitre.org/techniques/T1187/"]
 40risk_score = 47
 41rule_id = "6756ee27-9152-479b-9b73-54b5bbda301c"
 42severity = "medium"
 43tags = [
 44    "Domain: Endpoint",
 45    "OS: Windows",
 46    "Use Case: Threat Detection",
 47    "Tactic: Credential Access",
 48    "Data Source: Elastic Defend",
 49    "Data Source: Windows Security Event Logs",
 50    "Data Source: Microsoft Defender XDR",
 51    "Data Source: Crowdstrike",
 52    "Resources: Investigation Guide",
 53]
 54timestamp_override = "event.ingested"
 55type = "esql"
 56
 57query = '''
 58from logs-endpoint.events.process-*, logs-windows.sysmon_operational-*, logs-system.security-*, logs-windows.*, winlogbeat-*, logs-crowdstrike.fdr*, logs-m365_defender.event-* METADATA _id, _version, _index
 59| where
 60    event.category == "process" and
 61    event.type == "start" and
 62    process.name == "rundll32.exe" and
 63    process.command_line like "*DavSetCookie*"
 64| keep host.id, process.command_line, user.name, user.id
 65// extract the host from the WebDAV URL authority, excluding optional credentials and port
 66| grok process.command_line """(?i:https?)://(?:[^/@\s]+@)?(?<Esql.server_webdav_server>[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*)"""
 67| eval Esql.server_webdav_server = TO_LOWER(Esql.server_webdav_server)
 68| where
 69    Esql.server_webdav_server is not null and
 70    not Esql.server_webdav_server in ("www.google.com", "www.elastic.co", "google.com", "github.com", "www.github.com", "sharepoint.com", "live.net") and
 71    not Esql.server_webdav_server like ("*.live.net", "*.sharepoint.com") and
 72    // excludes private IP ranges
 73    not Esql.server_webdav_server rlike """(10\.(\d{1,3}\.){2}\d{1,3}|172\.(1[6-9]|2\d|3[0-1])\.(\d{1,3}\.)\d{1,3}|192\.168\.(\d{1,3}\.)\d{1,3})"""
 74| stats
 75    Esql.event_count = count(*),
 76    Esql.host_id_count_distinct = count_distinct(host.id),
 77    Esql.host_id_values = values(host.id),
 78    Esql.user_name_values = values(user.name)
 79  by Esql.server_webdav_server
 80| where
 81    Esql.host_id_count_distinct == 1 and Esql.event_count <= 3
 82| eval host.id = MV_MIN(Esql.host_id_values), user.name = MV_MIN(Esql.user_name_values), destination.domain = MV_MIN(Esql.server_webdav_server)
 83| KEEP host.id, user.name, destination.domain, Esql.*
 84'''
 85
 86setup = """## Setup
 87
 88This 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.
 89
 90Setup instructions: https://ela.st/install-elastic-defend
 91
 92### Additional data sources
 93
 94This rule also supports the following third-party data sources. For setup instructions, refer to the links below:
 95
 96- [CrowdStrike](https://ela.st/crowdstrike-integration)
 97- [Microsoft Defender XDR](https://ela.st/m365-defender)
 98- [Sysmon Event ID 1 - Process Creation](https://ela.st/sysmon-event-1-setup)
 99- [Windows Process Creation Logs](https://ela.st/audit-process-creation)
100"""
101
102
103[[rule.threat]]
104framework = "MITRE ATT&CK"
105
106[[rule.threat.technique]]
107id = "T1187"
108name = "Forced Authentication"
109reference = "https://attack.mitre.org/techniques/T1187/"
110
111[rule.threat.tactic]
112id = "TA0006"
113name = "Credential Access"
114reference = "https://attack.mitre.org/tactics/TA0006/"
115
116[[rule.threat]]
117framework = "MITRE ATT&CK"
118
119[[rule.threat.technique]]
120id = "T1218"
121name = "System Binary Proxy Execution"
122reference = "https://attack.mitre.org/techniques/T1218/"
123
124[[rule.threat.technique.subtechnique]]
125id = "T1218.011"
126name = "Rundll32"
127reference = "https://attack.mitre.org/techniques/T1218/011/"
128
129[rule.threat.tactic]
130id = "TA0005"
131name = "Defense Evasion"
132reference = "https://attack.mitre.org/tactics/TA0005/"