As MITRE says on its website, adversaries dump credentials to obtain login credentials to perform lateral movement when they got access to a computer. Several tools and techniques may be used to dump credentials of a computer. Here, I will try to show two different credential dumping techniques and prevention of it using FireEye’s Endpoint Security product, as a quick demo.
Before demo, I wanna give a short brief about lsass. LSA (Local Security Authority) is a process that authenticates user to computer. It checks SAM (Security Accounts Manager) database to validate user information. LSASS.exe (Local Security Authority Subsystem Service) is the process that is responsible for enforcing the local security policy on the system. If someone can dump lsass on the computer and get this dump file, it means the users’ credentials are stolen because lsass stores the credentials as clear text.
FireEye HX Process Guard
HX is the Endpoint Security producth of FireEye as you know already. I will not explain what it is and what it does here but typically it is an EDR solution with AV and some other prevention modules also. I wanted to try its Process Guard module, basically blocking attackers to dump lsass process.
“The Process Guard Module for FireEye Endpoint Security prevents attackers from obtaining access to credential data or key material stored within the lsass.exe process, thus protecting endpoints against common credential theft attacks” says FireEye about Process Guard.
Here, I will try to show some dump techniques to dump lsass and how Process Guard preventing it. This techniques are associated to MITRE ATT&CK (r) Tactic: Credential Access and Technique: T1003
Credential Dumping with comsvcs.dll
comsvcs.dll is a part of Windows OS. It is a system file and hidden. It is found in \Windows\System32 and can call minidump with rundll32.exe, so it can be used to dump credentials via lsass.exe process.
Firstly, process ID of lsass.exe process must be identified;
Then, the command below will dump the lsass;
A file about 48MBs being created with this process;
Now, it is time to use Mimikatz and get the passwords as clear text or hashes of the passwords (depends on the OS);
As you can see, it is very easy to get the credentials of the user of a compromised computer, if you do not prevent lsass.exe process against malicious behaviours. Now, I will try to prevent it using FireEye HX’s Process Guard module. For this, I enable Process Guard module on my computer’s policy;
lsass dump command again;
After that, when I check the created dump file, I can see a 0MB sized file has been created;
When I check Process Guard module in HX’s console, I can see HX has detected this behavior done by PowerShell;
Credential Dump with ProcDump
ProcDump is a Sysinternals tool used to generate memory dumps of applications. After disabled Process Guard module on HX again, I try to dump lsass using ProcDump;
A 48MBs sized file has been created;
Again Mimikatz and get the passwords or hashes (depends on the OS);
Then, let’s try again after enabling Process Guard. I try ProcDump again, but this time Process Guard is enabled;
It got error while creating the file and could not create any dump file.
NOTE 1: This tests are done while Antivirus of HX is disabled. Otherwise, AV would block and delete or quarantine Mimikatz. This is an alarm of this behavior;
NOTE 2: Even if you do not enable Process Guard and Antivirus at the same time, HX generates an IOC alert for these attacks. The IOC says us “-ma” command is being used with “lsass.exe” on cmd. This attack and IOC are associated to MITRE ATT&CK (r) Tactic: Credential Access and Technique: T1003