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Worm Attack

Worm Attack. Yuan Xue Fall 2012. Background. What is worm? Self-propagating malicious code History Morris worm was one of the first worms distributed over Internet Timeline of notable worms http://en.wikipedia.org/wiki/Timeline_of_notable_computer_viruses_and_worms Two examples

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Worm Attack

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  1. Worm Attack Yuan Xue Fall 2012

  2. Background • What is worm? • Self-propagating malicious code • History • Morris worm was one of the first worms distributed over Internet • Timeline of notable worms • http://en.wikipedia.org/wiki/Timeline_of_notable_computer_viruses_and_worms • Two examples • Code Red – 2001, MS IIS • Slammer – 2003, MS SQL • Samy (MySpace Worm) – 2005, XSS • Two topics • System vulnerability • Propagation model

  3. Slammer (Sapphire) Worm • When • Jan 25 2003 • How • Exploit Buffer-overflow with MS SQL/MS SQL Server Desktop Engine (known vulnerability, July 2002) • Scale • At least 74,000 hosts • Feature • Fast propagation speed (>55million scans per second, two orders of magnitude faster than Code Red worm) • No harmful payload • Countermeasure • Patch • Firewall (port blocking)

  4. Scale The diameter of each circle is a function of the logarithm of the number of infected machines, so large circles visually underrepresent the number of infected cases in order to minimize overlap with adjacent locations

  5. Details of Slammer Worm • SQL server vulnerability • The SSRS (SQL Server Resolution Service (SSRS) ) contains a stack buffer overflow that allows an attacker to execute arbitrary code by sending a crafted request to port 1434/udp • The code within such a request will be executed by the server host with the privileges of the SQL Server service account. • Slammer worm • Crafts packets of 376-bytes and send them to a chosen IP addresses on port 1434/udp • Random scanning • Randomly select IP addresses • If the packet is sent to a vulnerable machine, this victim machine will become infected and will also begin to propagate.

  6. Buffer Overflow Buffer overflow is an anomalous condition where a program writes data beyond the allocated end of a buffer in memory. • The techniques to exploit a buffer overflow vulnerability vary per architecture, operating system and memory region • Heap-based buffer overflow • stack-based buffer overflow • The program's code and data consisting of the program's instructions and the initialized and uninitialized static and global data • Run-time heap (created using malloc/calloc) • Users stack. This stack is used whenever a function call is made. Linux system memory layout

  7. Buffer Overflow • Stack-based buffer overflow • An example void function (int a, int b, int c){ char buffer1[5]; char buffer2[10]; } int main(){ function(1,2,3); }

  8. Buffer Overflow • Stack-based buffer overflow • Overwrite a function's return address, which in turn can alter the program's execution path void function (char *str) { char buffer[16]; strcpy (buffer, str); } int main () { char *str = "I am greater than 16 bytes"; // length of str = 27 bytes function (str); } • Function's return address is the address of the next instruction in memory, which is executed immediately after the function returns.

  9. Buffer Overflow • Stack-based buffer overflow • Overwrite a function's return address, which in turn can alter the program's execution path • Hacker can spawn a shell (with root permissions) by jumping the execution path to such code. • If there is no such code in the program to be exploited • Place the code we are trying to execute in the buffer's overflowing area. • Overwrite the return address so it points back to the buffer and executes the intended code. • Such code can be inserted into the program using environment variables or program input parameters.

  10. Propagation Model • Random Scanning • Initially spread exponentially, slows as the worms retry infected or immune addresses • Probes of Slammer worm from Dshield data set • Initially matched random scanning worm • Soon slowed down due to bw saturation and network failures Probe rate of Code red worm (a typical random-scanning worm)

  11. Why Slammer Was So Fast? • Bandwidth constraint vs. delay constraint • Slammer 404 bytes (376 payload) UDP based-- bandwidth constraint • Code Red 4K bytes TCP based – delay constraint • UDP vs. TCP

  12. How to Defend? • Buffer Overflow • Write secure code • Use of safe libraries • Compiler tools • Choice of programming language • Dynamic run-time checks • Executable space protection • Stack-smashing protection • Worm • Patch • MS has released the patch before the worm attack happens • Firewall • IDS • Deep packet inspection • Architecture • Address space layout randomization

  13. Reference • Worm • A Taxonomy of Computer Worms • en.wikipedia.org/wiki/Computer_worm • Slammer Worm • http://www.microsoft.com/sql/prodinfo/previousversions/letter.mspx • http://www.cert.org/advisories/CA-2003-04.html • Inside the Slammer Worm, IEEE S&P 2003 • Network Telescope • http://en.wikipedia.org/wiki/Network_telescope • http://www.caida.org/research/security/telescope/

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