[New Rule] Unusual Web Config File Access (#4927)

* [New Rule] Unusual Web Config File Access

* Update credential_access_web_config_file_access.toml

Author: w0rk3r

rules/windows/credential_access_web_config_file_access.toml

@@ -0,0 +1,63 @@
+[metadata]
+creation_date = "2025/07/23"
+integration = ["endpoint"]
+maturity = "production"
+updated_date = "2025/07/23"
+
+[rule]
+author = ["Elastic"]
+description = """
+Detects unusual access to the web.config file, which contains sensitive credential information such as database
+connection strings, machineKey validation/decryption keys, and SAML/OAuth token settings. Attackers can use the
+information extracted to forge malicious __VIEWSTATE requests for persistent RCE on the web server or pivot to the SQL
+server using exposed connection strings.
+"""
+from = "now-9m"
+index = ["logs-endpoint.events.file-*"]
+language = "kuery"
+license = "Elastic License v2"
+name = "Unusual Web Config File Access"
+references = [
+    "https://unit42.paloaltonetworks.com/microsoft-sharepoint-cve-2025-49704-cve-2025-49706-cve-2025-53770/",
+]
+risk_score = 47
+rule_id = "5841b80f-a1f8-4c00-a966-d2cc4a7a82e4"
+severity = "medium"
+tags = [
+    "Domain: Endpoint",
+    "OS: Windows",
+    "Use Case: Threat Detection",
+    "Tactic: Credential Access",
+    "Data Source: Elastic Defend",
+]
+timestamp_override = "event.ingested"
+type = "new_terms"
+
+query = '''
+event.category:file and host.os.type:windows and event.action:open and
+  file.name:"web.config" and file.path : *VirtualDirectories*
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1003"
+name = "OS Credential Dumping"
+reference = "https://attack.mitre.org/techniques/T1003/"
+
+
+
+[rule.threat.tactic]
+id = "TA0006"
+name = "Credential Access"
+reference = "https://attack.mitre.org/tactics/TA0006/"
+
+[rule.new_terms]
+field = "new_terms_fields"
+value = ["process.executable", "user.id"]
+[[rule.new_terms.history_window_start]]
+field = "history_window_start"
+value = "now-7d"
+
+