Return to Libc: Linux Exploit Development

Overview

• ret2libc (Return to libc): An exploit technique in Linux to exploit vulnerabilities by calling libc functions.
• Purpose: To bypass Data Execution Prevention (DEP) and execute commands like system(/bin/sh) to gain shell access.

Key Concepts

• Libc: Standard C library containing essential functions like system().
• DEP: A security feature preventing execution of code in non-executable memory segments.
• ASLR (Address Space Layout Randomization): Randomizes memory addresses to prevent exploitation.

Requirements

• Knowledge of where libc is loaded at runtime.
• Address calculation using a pointer leaked from a vulnerability like format string vulnerability.

Steps to Conduct Ret2libc Attack

1. Overwriting the Return Address

• Vulnerable Code: Program allows input overflow into a buffer, potentially overwriting return address.
• Vulnerability: Call to fgets() allows 1000 bytes into a buffer meant for 100 bytes.
• Technique: Use overflow to overwrite the return address with a controlled value.

2. Address Offset Consistency

• ASLR Impact: Addresses change but offsets between them remain consistent.
• Offset Calculation: Leverage consistent offsets to calculate function addresses in libc.

3. Ret2libc Attack Steps

• Step 1: Obtain libc address through format string vulnerability.
• Step 2: Calculate libc base address from the obtained pointer.
• Step 3: Calculate function addresses (e.g., system()) using base address.
• Step 4: Use another vulnerability like buffer overflow to overwrite the return address.

4. Finding Libc Base Address

• Format String Vulnerability: Leak a pointer from the stack pointing to libc.
• GDB Tools: Use GDB’s r and vmmap commands to map memory.

5. Calculating Function Addresses

• system() Address: Add known offsets to libc base to find system().
• /bin/sh Address: Locate /bin/sh string in libc using GDB search.
• POP RDI ROP Gadget: Use gadget to set pointer to /bin/sh in RDI.
• exit() Address: Similar calculation to system() to cleanly exit.

Exploit Script

1. Leak libc base address using format string vulnerability.
2. Calculate necessary function addresses using offsets.
3. Create ROP chain:
   • Use "quit" to exit loop.
   • Send 116 A's to hit return address.
   • Use POP RDI gadget to set RDI to /bin/sh.
   • Call system(), then exit().

Conclusion

• Successful execution leads to a shell via ret2libc.
• Ensures understanding of exploiting memory vulnerabilities in Linux using ret2libc.

Contact Information

• Phone: 571-969-7039