Relocation Bonus Attacking the Windows Loader

Architecture and Background

The arbiters of defense wield many static analysis tools; disassemblers, PE viewers, and anti-viruses are among them. When you peer into their minds, these tools reveal their perilous implementations of PE file parsing.

Vulnerability Analysis

They assume PE files come as-is, but the Windows Loader actually applies many mutations (some at the command of the PE itself) before execution ever begins. This talk is about bending that loader to one's whim with the Relocations Table as a command spell. It will demonstrate how the loader can be instrumented into a mutation engine capable of transforming an utterly mangled PE file into a valid executable.

Exploitation and Demonstrations

This method starts with multiple ASLR Preselection attacks that force binary mapping at a predictable address. It then mangles the PE file, garbling any byte not required prior to relocation. Finally, it embeds a new Relocations Table which, when paired with a preselected base address, causes the loader to reconstruct the PE and execute it with ease.

Remediation and Defensive Strategies

This isn't a packer or a POC, it is a PE rebuilder which generates completely valid, stable, and vastly tool-breaking executables. This talk will show you how this attack twists the protocols of a machine against the controls meant to protect it. It flexes on tools with various look-what-I-can-break demonstrations and, if you write similar tools, it'll make you rethink how you do it.