PH_Rule_SIGMA_1770
Enabled
Detects an Excel process that opens suspicious network connections to non-private IP addresses, and attempts to cover CVE-2021-42292. You will likely have to tune this rule for your organization, but it is certainly something you should look for and could have applications for malicious activity beyond CVE-2021-42292. . This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/network_connection/net_connection_win_excel_outbound_network_connection.yml
5
Security
Execution
Execution consists of techniques that result in adversary-controlled code running on a local or remote system. Techniques that run malicious code are often paired with techniques from all other tactics to achieve broader goals, like exploring a network or stealing data. For example, an adversary might use a remote access tool to run a PowerShell script that does Remote System Discovery.
https://attack.mitre.org/tactics/TA0002T1203
Exploitation for Client Execution
Adversaries may exploit software vulnerabilities in client applications to execute code. Vulnerabilities can exist in software due to unsecure coding practices that can lead to unanticipated behavior. Adversaries can take advantage of certain vulnerabilities through targeted exploitation for the purpose of arbitrary code execution. Several types exist: Browser-based Exploitation, Office Applications and Common Third-party Applications.
https://attack.mitre.org/techniques/T1203Server
Windows Sysmon via FortiSIEM Agent
Correlation
No remediation guidance specified
If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.
300 seconds
If the following defined pattern/s occur within a 300 second time window.
Filter
This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.
This is the query logic that matches incoming events
eventType REGEXP "Win-Sysmon-3-Network-Connect.*" AND (procName REGEXP ".*\\excel\.exe" AND initiated="true" AND isIpv6="false") AND destIpAddr NOT IN (Group@PH_SYS_NETWORK_ENTERPRISE_INTERNAL_NET)
This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID
destIpAddr,hostName,initiated,isIpv6,procName
This is most typically a numerical constraint that defines when the rule should trigger an incident
COUNT(*) >= 1
This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.
The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern
destIpAddr = Filter.destIpAddr,
hostName = Filter.hostName,
initiated = Filter.initiated,
isIpv6 = Filter.isIpv6,
procName = Filter.procName