Access Token Theft and Manipulation Attacks – A Door to Local Privilege Escalation

Executive Summary

Many malware attacks designed to inflict damage on a network are armed with lateral movement capabilities. Post initial infection, such malware would usually need to perform a higher privileged task or execute a privileged command on the compromised system to be able to further enumerate the infection targets and compromise more systems on the network. Consequently, at some point during its lateral movement activities, it would need to escalate its privileges using one or the other privilege escalation techniques. Once malware or an attacker successfully escalates its privileges on the compromised system, it will acquire the ability to perform stealthier lateral movement, usually executing its tasks under the context of a privileged user, as well as bypassing mitigations like User Account Control.

Process access token manipulation is one such privilege escalation technique which is widely adopted by malware authors. These set of techniques include process access token theft and impersonation, which eventually allows malware to advance its lateral movement activities across the network in the context of another logged in user or higher privileged user.

When a user authenticates to Windows via console (interactive logon), a logon session is created, and an access token is granted to the user. Windows manages the identity, security, or access rights of the user on the system with this access token, essentially determining what system resources they can access and what tasks can be performed. An access token for a user is primarily a kernel object and an identification of that user in the system, which also contains many other details like groups, access rights, integrity level of the process, privileges, etc. Fundamentally, a user’s logon session has an access token which also references their credentials to be used for Windows single sign on (SSO) authentication to access the local or remote network resources.

Once the attacker gains an initial foothold on the target by compromising the initial system, they would want to move around the network laterally to access more resource or critical assets. One of the ways for an attacker to achieve this is to use the identity or credentials of already logged-on users on the compromised machine to pivot to other systems or escalate their privileges and perform the lateral movement in the context of another logged on higher privileged user. Process access token manipulation helps the attackers to precisely accomplish this goal.

For our YARA rule, MITRE ATT&CK techniques and to learn more about the technical details of token manipulation attacks and how malware executes these attacks successfully at the code level, read our complete technical analysis here.

Coverage

McAfee On-Access-Scan has a generic detection for this nature of malware  as shown in the below screenshot:

Additionally, the YARA rule mentioned at the end of the technical analysis document can also be used to detect the token manipulation attacks by importing the rule in the Threat detection solutions like McAfee Advance Threat Defence, this behaviour can be detected.

Summary of the Threat

Several types of malware and advanced persistent threats abuse process tokens to gain elevated privileges on the system. Malware can take multiple routes to achieve this goal. However, in all these routes, it would abuse the Windows APIs to execute the token stealing or token impersonation to gain elevated privileges and advance its lateral movement activities.

• If the current logged on user on the compromised or infected machine is a part of the administrator group of users OR running a process with higher privileges (e.g., by using “runas” command), malware can abuse the privileges of the process’s access token to elevate its privileges on the system, thereby enabling itself to perform privileged tasks.
• Malware can use multiple Windows APIs to enumerate the Windows processes running with higher privileges (usually SYSTEM level privileges), acquire the access tokens of those processes and start new processes with the acquired token. This results in the new process being started in the context of the user represented by the token, which is SYSTEM.
• Malware can also execute a token impersonation attack where it can duplicate the access tokens of the higher privileged SYSTEM level process, convert it into the impersonation token by using appropriate Windows functionality and then impersonate the SYSTEM user on the infected machine, thereby elevating its privileges.
• These token manipulation attacks will allow malware to use the credentials of the current logged on user or the credentials of another privileged user to authenticate to the remote network resource, leading to advancement of its lateral movement activities.
• These attack techniques allows malware to bypass multiple mitigations like UAC, access control lists, heuristics detection techniques and allowing malware to remain stealthier while moving laterally inside the network.

Access Token Theft and Manipulation Attacks – Technical Analysis

Access Token Theft and Manipulation Attacks – A Door to Local Privilege Escalation.

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