buffer overflows

An analysis of stack based vulnerabilities

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A short presentation I gave summarizing a project I completed for a graduate course in Network Security


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An analysis of stack based vulnerabilities

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1972: First recorded overflow vulnerability by the Computer Security Technology Planning Study

1988: The Morris worm becomes the first major Internet Worm

2001: Red Code I & II Infect hundreds of thousands of hosts

2003: SQL Slammer (aka Sapphire) becomes the fastest spreading worm in modern history

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Overflow vulnerabilities are not obvious from source code inspection alone

Linking to any vulnerable library effectively makes an application vulnerable

Effective protection may require special OS and compiler configuration

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Major CPU elements include: Memory

• Paged, Hardware protected Registers

• Move data from memory to other hardware Control Unit

• Send OpCodes, Operands, HW Signals ALU

• Perform OpCodes, set status flags

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Standardized mnemonic references for hardware supported operations• Hardware OpCode: 0x0305000000• Assembly Instruction: ADD R0, R1

All high level languages ultimately compiled, assembled, linked, and loaded

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Stack: First in, last out data structure implemented on reserved memory page

Every procedure is given a stack frame Procedures allocate space for local

variables within their frame New frame is pushed onto the stack

when a procedure is called, popped off on return

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1. Write malicious payload assembly program

2. Compile, determine OpCodes, encode in hexadecimal string

3. Overflow target buffer with addresses pointing to injected code

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Key Defensive Goals:• Make target address guess difficult• Detect or prevent the attempt at run-time

Developers:• Safe Libraries• Stack Protecting Compilers• Static Code Analysis

Hardware• NX Memory Page Bit (Sun SPARC, IBM

PowerPC, newer Intel x86-64)

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Operating System• Address Space Randomization (Linux,

Windows Vista/Server2008, some support in Mac OS 10.5)

• Memory Page protection (OpenBSD derivatives, Windows if harware supports it)

• The combination of these two techniques has great potential

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Defenses are being developed in a wide cross section of areas

Rate of new attack ideas is limited in scope and incidence • return-to-libc, format string errors

Operating system defenses will probably remove this threat one day

Best present advice: Deploy all important patches!

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[1] Alan Clements. Principles of Computer Hardware. OxfordUniversity Press, Inc., New York, NY, USA, 2000.

[2] John L. Hennessy and David A. Patterson. Computer architecture:a quantitative approach. Morgan Kaufmann PublishersInc., San Francisco, CA, USA, 2002.

[3] Intel. Intel Architecture Software Developers Manual. Volume1: Basic Architecture, 1999.

[4] Intel. Intel Architecture Software Developers Manual. Volume2: Instruction Set Reference, 1999

[5] Elias Levy. Smashing the stack for fun and profit. InternetArticle, 1996. Accessed on November 11, 2008 from http://insecure.org/stf/smashstack.html.

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