@Yuan Xue Worm Attack Yuan Xue Fall 2012

@Yuan Xue Background What is worm? Self-propagating malicious code History Morris worm was one of the first worms distributed over Internet Timeline of notable worms  _worms _worms Two examples Code Red – 2001, MS IIS Slammer – 2003, MS SQL Samy (MySpace Worm) – 2005, XSS Two topics System vulnerability Propagation model

@Yuan Xue Slammer (Sapphire) Worm When Jan 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)

@Yuan Xue 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

@Yuan Xue 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.

@Yuan Xue Buffer Overflow The techniques to exploit a buffer overflow vulnerability vary per architecture, operating system and memory region Heap-based buffer overflow stack-based buffer overflow Linux system memory layout Buffer overflow is an anomalous condition where a program writes data beyond the allocated end of a buffer in memory. 1.The program's code and data consisting of the program's instructions and the initialized and uninitialized static and global data 2.Run-time heap (created using malloc/calloc) 3.Users stack. This stack is used whenever a function call is made.

@Yuan Xue 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); }

@Yuan Xue 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.

@Yuan Xue 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.

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

@Yuan Xue 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

@Yuan Xue 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

@Yuan Xue Reference Worm A Taxonomy of Computer Worms A Taxonomy of Computer Worms en.wikipedia.org/wiki/Computer_worm Slammer Worm letter.mspx letter.mspx Inside the Slammer Worm, IEEE S&P 2003 Network Telescope