## 6 Analysis of Post-Exploitation Behavior and Defense Mechanisms  
Given the results presented in Section 5, a thorough understanding of the C3's post-exploitation behavior is crucial. Therefore, we proceed with an analysis and offer suggestions for detecting this activity. Several potential detection points emerge. First, the -_load-extension_ flag is present in the browser's process execution, providing a readily identifiable characteristic. Second, communication between the extension and the native application consistently involves a command-prompt (cmd) process initiated as a subprocess of the Chrome browser. Third, this communication occurs in cleartext, enabling EDR solutions to inspect the exchanged messages. Fourth, command executions, such as ping 8.8.8.8, spawn additional child processes of the native application. Specifically, the process flow is as follows: chrome\(\rightarrow\)cmd\(\rightarrow\)native_messaging\(\rightarrow\)cmd\(\rightarrow\)PING. This distinct process hierarchy offers a clear indicator of potentially malicious subprocesses originating from the Chrome browser. Consequently, to detect this post-exploitation activity, the YARA rule in Listing 1 can serve as a PoC. It is important to note that this rule is tailored to the specific implementation described herein and functions as a signature-based detection method. The rule searches for Chrome or MSEdge process executions that include a cmd process, an _.exe_ process, and the -_load-extension_ string. To utilize this YARA rule, the appropriate executable can be downloaded from the official VirusTotal YARA repository [15]. ```
1:functionDetect_Browser_CMD_Execution(input_data)
2:Define suspicious_strings:
3:browser_chrome \(\leftarrow\) \"chrome.exe\" (nocase)
4:browser_edge \(\leftarrow\) \"msede.exe\" (nocase)
5:cmd \(\leftarrow\) \"cmd.exe\" (nocase)
6:exe \(\leftarrow\) \".exe\" (nocase)
7: suspicious_string \(\leftarrow\) \"-load-extension\" (nocase)
8:ifbrowser_chrome or browser_edge in input_data then
9:ifcmd in input_data then
10:ifexe in input_data then
11:if suspicious_string in input_data then
12:return \"Suspicious Execution Detected\"
13:endif
14:endif
15:endif
16:endif
17:return \"No Suspicious Activity Detected\"
18:endfunction
```  
**Listing 1**. Detection of suspicious CMD execution initiated by a browser. An additional defense strategy against this post-exploitation technique in Microsoft Windows-based enterprise environments involves leveraging Group Policy Objects (GPOs) within Active Directory. A specifically configured GPO can mitigate this attack by preventing the installation and execution of browser extensions. This involves first downloading the Windows-specific ADMX template for each target browser and adding it to the Group Policy Management Editor. Subsequently, the extension installation blocklist should be enabled and configured with the asterisk (*) wildcard value. This configuration blocks the execution of all extensions not explicitly included in the allowlist. Finally, the allowlist must be enabled and populated with the extension IDs of permitted extensions. However, GPO policies are susceptible to circumvention under certain conditions. Misconfigurations, such as applying the policy at the user level instead of the machine level, can enable users to bypass restrictions by switching user profiles or employing alternative methods, including portable browsers or unmanaged software. Furthermore, an attacker could circumvent the policy by utilizing a portable browser that does not adhere to system-wide settings or by switching to a different installed browser not subject to the policy. For example, if the GPO is enforced for Chrome but not MSEdge, an attacker could simply switch browsers to evade the restriction. Concerning shortcut files, enterprise-managed Windows workstations typically store shortcuts created after application installation in the C:\Users\Public\Desktop directory. By default, all authenticated users possess \"Modify\" (M) permissions within this location.