Detection rules › Splunk
Potential CVE-2024-21413: Outbound SMB from Outlook (Windows Event Log)
A critical vulnerability CVE-2024-21413 in Microsoft Outlook, discovered by Check Point, enables remote code execution from merely opening an email containing malicious links, bypassing Outlook's Protected View. This flaw, exploitable without user interaction, allows attackers to perform high-privilege actions and steal NTLM credentials via crafted Office documents. This use case detects outbound SMB connections from Outlook which may indicate successful CVE-2024-21413 execution.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Execution | T1204.001 User Execution: Malicious Link |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Security-Auditing | Event ID 5156 | The Windows Filtering Platform has permitted a connection. |
Rule body yaml
id: '28360.51640'
title: 'Potential CVE-2024-21413: Outbound SMB from Outlook'
description: A critical vulnerability CVE-2024-21413 in Microsoft Outlook, discovered
by Check Point, enables remote code execution from merely opening an email containing
malicious links, bypassing Outlook's Protected View. This flaw, exploitable without
user interaction, allows attackers to perform high-privilege actions and steal NTLM
credentials via crafted Office documents. This use case detects outbound SMB connections
from Outlook which may indicate successful CVE-2024-21413 execution.
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_winevent` (EventCode=5156 OR "<EventID>5156<")
(TERM(445) OR TERM(SMB)) "outlook.exe" | where match(dest_port, "^445$") and match(process_name,
"(?i)outlook\.exe") and not match(dest_ip, "^(10\.|172\.(1[6-9]|2[0-9]|3[0-1])\.|192\.168\.|fc00:|fd00:|fe80:)")
| table _time, host, user, dest_ip, dest_port, process_* | bin span=1s | stats values(*)
as * by _time, host '
techniques:
- execution:user execution:malicious link
technique_id:
- T1204.001
data_category:
- Windows event logs
- Process use of network
references:
- https://research.checkpoint.com/2024/the-risks-of-the-monikerlink-bug-in-microsoft-outlook-and-the-big-picture/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_winevent` (EventCode=5156 OR "<EventID>5156<") (TERM(445) OR TERM(SMB)) "outlook.exe"
Stage 2: where
| where match(dest_port, "^445$") and match(process_name, "(?i)outlook\.exe") and not match(dest_ip, "^(10\.|172\.(1[6-9]|2[0-9]|3[0-1])\.|192\.168\.|fc00:|fd00:|fe80:)")
Stage 3: table
| table _time, host, user, dest_ip, dest_port, process_*
Stage 4: bucket
| bin span=1s
Stage 5: stats
| stats values(*) as * by _time, host
Exclusions
Top-level NOT(...) conjuncts: predicates this rule actively suppresses.
| Field | Kind | Excluded values |
|---|---|---|
dest_ip | match | "^(10\.|172\.(1[6-9]|2[0-9]|3[0-1])\.|192\.168\.|fc00:|fd00:|fe80:)" |
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
EventCode | eq |
|
dest_port | match |
|
process_name | match |
|
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | "<EventID>5156<" |
| 1 | TERM |
| 1 | 445 |
| 1 | TERM |
| 1 | SMB |
| 1 | "outlook.exe" |