Windows: Suspicious Teams Application Related ObjectAcess Event

Rule ID

PH_Rule_SIGMA_1848

Default Status

Enabled

Description

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/builtin/security/win_security_teams_suspicious_objectaccess.yml

Severity

MITRE ATT&CK® Tactics

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/TA0006

MITRE ATT&CK® Techniques

T1528

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/T1528

Impacts

Server

Data Source

Windows Security Log via OMI or FortiSIEM Agent

Detection

Correlation

Remediation Guidance

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.

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

Filter

SubPattern Definitions

SubPattern Name: Filter

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

(eventType="Win-Security-4663" AND osObjName REGEXP ".*\\Microsoft\\Teams\\Cookies.*|.*\\Microsoft\\Teams\\Local Storage\\leveldb.*") AND (procName NOT REGEXP ".*\\Microsoft\\Teams\\current\\Teams\.exe.*")

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

hostName,osObjName,procName

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

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

hostName = Filter.hostName,
osObjName = Filter.osObjName,
procName = Filter.procName

FortiSIEM Rules