Compiler Trojan Audit Guide

TL;DR

This guide shows you how to check open source compiler binaries for malicious code (trojans). It covers file hashing, signature verification, static analysis with tools like strings and disassemblers, and basic dynamic analysis. It’s not foolproof but significantly reduces risk.

1. Initial Checks: Hashes & Signatures

1. Download the Binary: Get the compiler from its official source (e.g., GitHub releases, project website).
2. Calculate File Hashes: Use tools like sha256sum or md5sum to create a hash of the downloaded file.

   sha256sum gcc-13.2.0-x86_64-linux-gnu.tar.xz

3. Verify Against Official Hashes: Compare your calculated hash with the official hashes published on the project’s website or in release notes. A mismatch means the file has been altered.
4. Check Digital Signatures (if available): Many projects sign their binaries for authenticity. Use tools like gpg to verify the signature.

   gpg --verify gcc-13.2.0-x86_64-linux-gnu.tar.xz.sig gcc-13.2.0-x86_64-linux-gnu.tar.xz

2. Static Analysis: Looking for Suspicious Patterns

1. Extract Strings: Use the strings command to find embedded text within the binary.

   strings gcc-13.2.0-x86_64-linux-gnu | less

   Look for unusual URLs, IP addresses, or references to unexpected files/directories.

2. Disassemble the Binary: Use a disassembler like objdump (Linux) or IDA Pro (commercial) to view the assembly code.

   objdump -d gcc-13.2.0-x86_64-linux-gnu | less

3. Identify Suspicious Functions: Look for calls to functions that are unusual for a compiler, such as network connections (e.g., socket()), file manipulation (e.g., fopen() with write access to unexpected locations), or process creation (e.g., fork(), exec()).
4. Examine Control Flow: Look for obfuscated code or unusual jumps/loops that might hide malicious logic.

3. Basic Dynamic Analysis: Running in a Safe Environment

1. Set up a Virtual Machine (VM): Use software like VirtualBox or VMware to create an isolated environment for testing. This prevents the trojan from harming your main system.
2. Run the Compiler: Compile a simple test program with the compiler binary.
3. Monitor System Calls: Use tools like strace (Linux) to observe the system calls made by the compiler during compilation. Look for unexpected file access, network connections, or process creation.

   strace gcc -v test.c 2>&1 | less

4. Monitor Network Activity: Use tools like tcpdump or Wireshark to monitor any network traffic generated by the compiler.
5. Check for File Modifications: After compilation, check if any unexpected files have been created or modified on your system.

4. Advanced Techniques (Optional)

• Sandboxing: Run the compiler in a sandbox environment to restrict its access to system resources.
• Decompilation: Use a decompiler to convert the assembly code back into C-like source code, making it easier to understand.
• Memory Analysis: Use tools like GDB to examine the compiler’s memory during runtime and look for suspicious data or code injections.

5. Reporting

If you find evidence of a trojan, report it immediately to the project maintainers and relevant cyber security authorities.