Rare Connection to WebDAV Target

 1[metadata]
 2creation_date = "2025/04/28"
 3integration = ["endpoint", "system", "windows", "m365_defender", "crowdstrike"]
 4maturity = "production"
 5updated_date = "2026/01/23"
 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[[rule.threat.technique]]
91id = "T1187"
92name = "Forced Authentication"
93reference = "https://attack.mitre.org/techniques/T1187/"
94
95
96[rule.threat.tactic]
97id = "TA0006"
98name = "Credential Access"
99reference = "https://attack.mitre.org/tactics/TA0006/"