Windows: Potential CVE-2021-42287 Exploitation Attempt

Rule ID

PH_Rule_SIGMA_1160

Default Status

Enabled

Description

Detects attempts to exploit CVE-2021-42287 (sAMAccountName spoofing, deceiving the KDC) by creating a computer object and clearing the attribute ServicePrincipalName on the computer object. Being the CREATOR OWNER, user gets granted additional permissions and can do many changes to the object. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/builtin/system/microsoft_windows_directory_services_sam/win_system_exploit_cve_2021_42287.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

T1558.003

Steal or Forge Kerberos Tickets: Kerberoasting

Adversaries may attempt to subvert Kerberos authentication by stealing or forging Kerberos tickets to enable Pass the Ticket. Adversaries may abuse a valid Kerberos ticket-granting ticket (TGT) or sniff network traffic to obtain a ticket-granting service (TGS) ticket that may be vulnerable to Brute Force. Cracked hashes may enable Persistence, Privilege Escalation, and Lateral Movement via access to Valid Accounts.

https://attack.mitre.org/techniques/T1558/003

Impacts

Server

Data Source

Windows System Log via OMI or FortiSIEM Agent

Detection

Correlation

Remediation Guidance

Determine if this was an authorized penetration testing 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.

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 IN ("Win-System-Microsoft-Windows-Directory-Services-SAM-16990","Win-System-Microsoft-Windows-Directory-Services-SAM-16991")

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

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

FortiSIEM Rules