Ret2dlresolve

👉 Overview

👀 What ?

Ret2dlresolve, short for 'return-to-dl-resolve', is an advanced binary exploitation technique used in cybersecurity. It is a method of defeating Address Space Layout Randomization (ASLR) by redirecting program execution to the 'dl-resolve' function within the system's dynamic linker. The dynamic linker is responsible for resolving symbolic references to dynamic libraries at run-time.

🧐 Why ?

Understanding Ret2dlresolve is vital for both offensive and defensive cybersecurity practitioners. On the offensive side, it presents a powerful tool for exploiting vulnerabilities in binary applications, especially those that use ASLR. On the defensive side, comprehending this technique can help in building more secure applications and systems, as well as detecting and responding to such attacks.

⛏️ How ?

Ret2dlresolve works by exploiting a vulnerability that allows control over the program's execution flow. The attacker then diverts the execution flow to the 'dl-resolve' function, passing it crafted data structures that cause it to load and execute a chosen function from a dynamic library, such as the 'system' function from libc. This, in turn, allows the attacker to execute arbitrary system commands.

⏳ When ?

The use of Ret2dlresolve as an exploitation technique has been prevalent since the early 2000s, following the widespread adoption of ASLR as a security measure in operating systems.

⚙️ Technical Explanations

At its core, Ret2dlresolve leverages the process of lazy binding. Lazy binding is a mechanism where the dynamic linker resolves symbols (like function names) only when they are first called, not when the program starts. When a function is called for the first time, an indirect call is made to 'dl-resolve', which resolves the symbol and replaces the function's entry in the Global Offset Table (GOT) with the actual address. In a Ret2dlresolve attack, an attacker crafts fake data structures to make 'dl-resolve' resolve a function of their choosing (like 'system'), and then modifies a function's GOT entry to point to this crafted data. This results in arbitrary command execution when the function is called next time. To successfully execute a Ret2dlresolve attack, an attacker needs a write-what-where condition and the ability to control the program’s execution flow.