Rare Connection to WebDAV Target

  1[metadata]
  2creation_date = "2025/04/28"
  3integration = ["endpoint", "system", "windows", "m365_defender", "crowdstrike"]
  4maturity = "production"
  5updated_date = "2026/03/24"
  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-3660s"
 15language = "esql"
 16license = "Elastic License v2"
 17name = "Rare Connection to WebDAV Target"
 18note = """## Triage and analysis
 19
 20### Investigating Rare Connection to WebDAV Target
 21
 22### Possible investigation steps
 23
 24- Examine the reputation of the destination domain or IP address.
 25- Verify if the target user opened any attachments or clicked links pointing to the same target within seconds from the alert timestamp.
 26- Correlate the findings with other security logs and alerts to identify any patterns or additional indicators of compromise related to the potential relay attack.
 27
 28### False positive analysis
 29
 30- User accessing legit WebDAV resources.
 31
 32### Response and remediation
 33
 34- Conduct a password reset for the target account that may have been compromised or are at risk, ensuring the use of strong, unique passwords.
 35- Verify whether other users were targeted but did not open the lure..
 36- 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.
 37- 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."""
 38references = ["https://attack.mitre.org/techniques/T1187/"]
 39risk_score = 47
 40rule_id = "6756ee27-9152-479b-9b73-54b5bbda301c"
 41severity = "medium"
 42tags = [
 43    "Domain: Endpoint",
 44    "OS: Windows",
 45    "Use Case: Threat Detection",
 46    "Tactic: Credential Access",
 47    "Data Source: Elastic Defend",
 48    "Data Source: Windows Security Event Logs",
 49    "Data Source: Microsoft Defender for Endpoint",
 50    "Data Source: Crowdstrike",
 51    "Resources: Investigation Guide",
 52]
 53timestamp_override = "event.ingested"
 54type = "esql"
 55
 56query = '''
 57from 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
 58| where
 59    @timestamp > now() - 8 hours and
 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 domain or IP address from process cmdline
 66| grok process.command_line """(?<Esql.server_webdav_server>((http|https)://[a-zA-Z0-9-\.]{1,}\.[a-zA-Z]{2,3}[@\/]+)|(\b(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\b)[@\/]+)"""
 67// remove sub domains from URL
 68| eval Esql.server_webdav_server = REPLACE(Esql.server_webdav_server, """((http|https)://[a-zA-Z0-9-]{1,}\.)""", "")
 69| eval Esql.server_webdav_server = REPLACE(Esql.server_webdav_server, "/", "")
 70| where
 71    Esql.server_webdav_server is not null and
 72    not Esql.server_webdav_server in ("www.google.com", "www.elastic.co", "sharepoint.com", "live.net", "google.com", "SHAREPOINT.COM", "github.com") and
 73    // excludes private IP ranges
 74    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})"""
 75| stats
 76    Esql.event_count = count(*),
 77    Esql.host_id_count_distinct = count_distinct(host.id),
 78    Esql.host_id_values = values(host.id),
 79    Esql.user_name_values = values(user.name)
 80  by Esql.server_webdav_server
 81| where
 82    Esql.host_id_count_distinct == 1 and Esql.event_count <= 3
 83| 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)
 84| KEEP host.id, user.name, destination.domain, Esql.*
 85'''
 86
 87
 88[[rule.threat]]
 89framework = "MITRE ATT&CK"
 90
 91[[rule.threat.technique]]
 92id = "T1187"
 93name = "Forced Authentication"
 94reference = "https://attack.mitre.org/techniques/T1187/"
 95
 96[rule.threat.tactic]
 97id = "TA0006"
 98name = "Credential Access"
 99reference = "https://attack.mitre.org/tactics/TA0006/"
100
101[[rule.threat]]
102framework = "MITRE ATT&CK"
103
104[[rule.threat.technique]]
105id = "T1218"
106name = "System Binary Proxy Execution"
107reference = "https://attack.mitre.org/techniques/T1218/"
108
109[[rule.threat.technique.subtechnique]]
110id = "T1218.011"
111name = "Rundll32"
112reference = "https://attack.mitre.org/techniques/T1218/011/"
113
114[rule.threat.tactic]
115id = "TA0005"
116name = "Defense Evasion"
117reference = "https://attack.mitre.org/tactics/TA0005/"