PH_Rule_SIGMA_1947
Enabled
Detects an access to authentication tokens and accounts of Microsoft Teams desktop application. There is a security vulnerability that Microsoft Teams stores user authentication tokens as cleartext in Windows, Linux, Mac. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/file/file_event/file_event_win_access_susp_teams.yml
7
Security
Credential Access
Credential Access consists of techniques for stealing credentials like account names and passwords. Techniques used to get credentials include keylogging or credential dumping. Using legitimate credentials can give adversaries access to systems, make them harder to detect, and provide the opportunity to create more accounts to help achieve their goals.
https://attack.mitre.org/tactics/TA0006T1528
Steal Application Access Token
Adversaries can steal user application access tokens as a means of acquiring credentials to access remote systems and resources. This can occur through social engineering and typically requires user action to grant access.
https://attack.mitre.org/techniques/T1528Server
Windows Sysmon via FortiSIEM Agent
Correlation
Determine if this was an authorized penetration testing activity or authorized sysadmin activity. Otherwise, there is no reason for this activity to be occurring. The host should be quarantined and investigated immediately. Collect the process hash and check for malware match. Investigate what other incidents are occurring on that host during that time frame. Vectra's recommendation is for users to switch to the browser version of the Microsoft Teams client.
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 fileName REGEXP ".*\\Microsoft\\Teams\\Cookies.*|.*\\Microsoft\\Teams\\Local Storage\\leveldb.*" AND (procName NOT REGEXP ".*\\Microsoft\\Teams\\current\\Teams\.exe.*")
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