The Chips N Crisp, unveiling the mysteries of chcp

Unveiling Hidden Commands

Delving into Lesser-Known Windows Secrets

Recently, I was investigating an incident, during the flow I created a table within the SIEM solution that displayed the attacker's _time, ProcessCommandLine, ParentProcessCommandLine, message, and more. I started analyzing the attacker's executed commands, which ranged from Active Directory enumerations to host enumerations and obfuscated PowerShell commands. However, one command that caught my attention was called Chcp.

Have you ever heard of the chcp command? I like to call it the "chips 'n' crisp" (Bro is delusional), but its main name is the code page. Now, let's dive into it. But first, let’s understand how the command line interprets the code we enter.

Command Line Demystified

Decoding Console Code Pages: A Deep Dive into CHCP

The active console code page is a crucial aspect of how text is displayed and interpreted in the Windows command prompt.

A code page is essentially a set of character codes used to decode text. The default code page is determined by the Windows Locale, but you can change it using the CHCP command, which stands for Change Code Page.

Why Does It Matter? Unveiling the Importance of Code Pages

• Character Display: The code page dictates which characters are displayed when you type in the command prompt. This is especially important when dealing with characters outside the standard ASCII range (0-127), like special symbols or characters from non-English languages.
• Session Specific: Any changes made to the code page using CHCP are only for the current session. If you open a new command prompt, it will use the default code page unless you change it again.

Real-World Applications: How to Use CHCP Effectively

1. Simply type CHCP in the command prompt, and it will display the current active code page number.
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C:\> CHCP
Active code page: 437

2. To change the code page, use CHCP followed by the code page number, For example, to change to code page 65001 (UTF-8), you would type:
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C:\> CHCP 65001

1. This command changes the code page for the current session to 65001.
3. If you start another command prompt from within the current one, it will inherit the new code page. For instance:
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C:\> CMD

1. The new command prompt window will use the code page 65001 set in the original session.

Top Code Pages You Should Know

Decoding Character Encoding Standards

ASCII: American Standard Code for Information Interchange, a 7-bit character encoding standard for text. Example: A is represented by 65.

Code Page Clues: Unmasking Attackers Through the chcp Command

C:\> chcp 

C:\> Active code page: 437

Unveiling Locale Secrets

• Attackers identify system locale settings (e.g., language, character encoding).
• Knowing the code page ensures their scripts or malware run without encoding errors.

Crafting Region-Specific Payloads

• A non-English code page (e.g., 850 for Western European languages) prompts attackers to use localized filenames, commands, or data formats.

Spotting Anomalies in Encoding Commands

• Security tools can flag unusual usage of chcp during odd times or by suspicious processes.
• Rare use by legitimate users makes it a potential red flag for malicious activity.

Turning Recon into a Defense Opportunity

• Alerting on such behavior offers early insight into possible reconnaissance attempts.
• Defenders can respond proactively to mitigate further malicious actions.

IcedID Detection through Code Page Change Monitoring

EDR agents detected chcp.exe being run by cmd.exe with specific command-line arguments. This activity can indicate malware, like IcedID, which uses this technique to determine the locale, language, or country of the compromised system. If malicious, this could lead to further system compromise and data exfiltration

Cracking the Code: MITRE ATT&CK

Resource Link: Command and Scripting Interpreter, Technique T1059 - Enterprise | MITRE ATT&CK®

KQL Command-Line Sleuth: Detecting Suspicious CodePage IcedID Switches via CHCP

We are going to write a Kusto Query Language (KQL) query to detect suspicious code page switches in command line.

SecurityEvent
| where ProcessName endswith "chcp.com"
| where CommandLine has_any (" 936", " 1258")
| project TimeGenerated, Computer, ProcessName, CommandLine, ParentCommandLine

Closing Thoughts

Written By: Sameer Fakhoury aka.semo