PH_Rule_SIGMA_853
Enabled
Detects suspicious activity in which the MSExchangeMailboxReplication process writes .asp and .apsx files to disk, which could be a sign of ProxyShell exploitation. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/file/file_event/file_event_win_susp_exchange_aspx_write.yml
7
Security
Persistence
Persistence consists of techniques that adversaries use to keep access to systems across restarts, changed credentials, and other interruptions that could cut off their access. Techniques used for persistence include any access, action, or configuration changes that let them maintain their foothold on systems, such as replacing or hijacking legitimate code or adding startup code.
https://attack.mitre.org/tactics/TA0003T1505.003
Server Software Component: Web Shell
Adversaries may backdoor web servers with web shells to establish persistent access to systems. A Web shell is a Web script that is placed on an openly accessible Web server to allow an adversary to use the Web server as a gateway into a network. A Web shell may provide a set of functions to execute or a command-line interface on the system that hosts the Web server.
https://attack.mitre.org/techniques/T1505/003Server
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="Win-Sysmon-11-FileCreate" AND procName REGEXP "\\MSExchangeMailboxReplication\.exe$" AND fileName REGEXP "\.asp$|\.aspx$"
This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID
fileName,hostName,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
fileName = Filter.fileName,
hostName = Filter.hostName,
procName = Filter.procName