Microsoft 365 Exchange Safe Attachment Rule Disabled

calendar May 22, 2024 · Domain: Cloud Data Source: Microsoft 365 Use Case: Configuration Audit Tactic: Defense Evasion  ·
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Identifies when a safe attachment rule is disabled in Microsoft 365. Safe attachment rules can extend malware protections to include routing all messages and attachments without a known malware signature to a special hypervisor environment. An adversary or insider threat may disable a safe attachment rule to exfiltrate data or evade defenses.

Elastic rule (View on GitHub)

 1[metadata]
 2creation_date = "2020/11/19"
 3integration = ["o365"]
 4maturity = "production"
 5updated_date = "2024/05/21"
 6
 7[rule]
 8author = ["Elastic"]
 9description = """
10Identifies when a safe attachment rule is disabled in Microsoft 365. Safe attachment rules can extend malware
11protections to include routing all messages and attachments without a known malware signature to a special hypervisor
12environment. An adversary or insider threat may disable a safe attachment rule to exfiltrate data or evade defenses.
13"""
14false_positives = [
15    """
16    A safe attachment rule may be disabled by a system or network administrator. Verify that the configuration change
17    was expected. Exceptions can be added to this rule to filter expected behavior.
18    """,
19]
20from = "now-30m"
21index = ["filebeat-*", "logs-o365*"]
22language = "kuery"
23license = "Elastic License v2"
24name = "Microsoft 365 Exchange Safe Attachment Rule Disabled"
25note = """## Setup
26
27The Office 365 Logs Fleet integration, Filebeat module, or similarly structured data is required to be compatible with this rule."""
28references = [
29    "https://docs.microsoft.com/en-us/powershell/module/exchange/disable-safeattachmentrule?view=exchange-ps",
30]
31risk_score = 21
32rule_id = "03024bd9-d23f-4ec1-8674-3cf1a21e130b"
33severity = "low"
34tags = [
35    "Domain: Cloud",
36    "Data Source: Microsoft 365",
37    "Use Case: Configuration Audit",
38    "Tactic: Defense Evasion",
39]
40timestamp_override = "event.ingested"
41type = "query"
42
43query = '''
44event.dataset:o365.audit and event.provider:Exchange and event.category:web and event.action:"Disable-SafeAttachmentRule" and event.outcome:success
45'''
46
47
48[[rule.threat]]
49framework = "MITRE ATT&CK"
50[[rule.threat.technique]]
51id = "T1562"
52name = "Impair Defenses"
53reference = "https://attack.mitre.org/techniques/T1562/"
54
55
56[rule.threat.tactic]
57id = "TA0005"
58name = "Defense Evasion"
59reference = "https://attack.mitre.org/tactics/TA0005/"

Setup

The Office 365 Logs Fleet integration, Filebeat module, or similarly structured data is required to be compatible with this rule.

References

  • Disable-SafeAttachmentRule (ExchangePowerShell)

    Safe Attachments is a feature in Microsoft Defender for Office 365 that opens email attachments in a special hypervisor environment to detect malicious activity. For more information, see Safe Attachments in Defender for Office 365. You need to be assigned permissions before you can run this cmdlet. Although this topic lists all parameters for the cmdlet, you may not have access to some parameters if they're not included in the permissions assigned to you. To find the permissions required to run any cmdlet or parameter in your organization, see Find the permissions required to run any Exchange cmdlet.


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