Use of fuzzing in detecting security vulnerabilities
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Use of Fuzzing in detecting security vulnerabilities. Biswajit Mazumder Rohit Hooda Arpan Chowdhary. Agenda. What is F uzzing ? Fuzzing techniques Types of F uzzing Fuzzing explained Case study and changes: SCRASHME sys_getdomainname () vmsplice () : Local Root Exploit Conclusion.

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Use of fuzzing in detecting security vulnerabilities

Use of Fuzzing in detecting security vulnerabilities





  • What is Fuzzing?

  • Fuzzing techniques

  • Types of Fuzzing

  • Fuzzing explained

  • Case study and changes: SCRASHME

  • sys_getdomainname()

  • vmsplice() : Local Root Exploit

  • Conclusion

What is fuzzing
What is Fuzzing?

  • Short for FUZZ-TESTING.

  • Technique of Black-box testing



Malformed / SemiMalformed

Random / Adaptive

Black Box

Crashes /

Information leaks /


Fuzzing techniques
Fuzzing Techniques

  • Event-Driven Fuzz

  • Character-Driven Fuzz

  • Database Fuzz

Types of fuzzing
Types of Fuzzing

Based on type of Fuzzer:

  • Tool oriented Fuzzing

  • Manual Fuzzing

    Based on Attack Targets:

  • Application fuzzing.

  • Protocol fuzzing.

  • File-format fuzzing.

  • Operating System fuzzing.

Fuzzing explained
Fuzzing Explained

  • Simple fuzz approach using a pseudo random number generator as input.

  • Validation of fuzz attempts to assure that the random input is reasonable.

  • A combined approach using valid test data and invalid random input interjection.

Case study scrashme
Case Study: SCRASHME

  • Open source system call fuzzer for Linux.

  • Stress tests system calls for robustness and security flaws.

  • -i: use sanitize methods before calling syscalls.

  • -c#: do syscall # with random inputs.

  • -C: check syscalls that call capable() return -EPERM.

  • -r: call random syscalls with random inputs.

  • -Sr: pass struct filled with random junk.

  • -Sxx: pass struct filled with hex value xx.

  • -x#: use value as register arguments.

  • -z: use all zeros as register parameters.

Scrashme changes

  • Support for new syscall #333 in Linux Kernel i.e. sys_getdomainname().

  • Sanitize method for Local root exploit for vmsplice() syscall.

Struct utsname

/* Structure describing the system and machine. */



/* Name of the implementation of the operating system. */


/* Name of this node on the network. */


/* Current release level of this implementation. */


/* Current version level of this release. */


/* Name of the hardware type the system is running on. */


/* Name of the domain of this node on the network. */

char domainname[_UTSNAME_DOMAIN_LENGTH];


Sys getdomainname

  • getdomainname () is used to access the domain name of the current processor/node.

  • getdomainname() currently calls uname() in the current versions of Linux Kernel.

  • setdomainname() is used to change the domain name of the current processor/node.

  • In a FQDN e.g. “mynetwork” is the domainname.

Sys getdomainname contd
sys_getdomainname() contd…

asmlinkage long sys_getdomainname(char __user *name, intlen) {


int err = -EINVAL;

+ if (len < 0 || len > __NEW_UTS_LEN)

+ goto done;


nlen = strlen(utsname()->domainname) + 1;

if (nlen < len)

len = nlen;

if ( copy_to_user(name, utsname()->domainname, len) ){

err = -EFAULT;

goto done;


err = 0;



return err;


What is vmsplice
What is vmsplice()?

  • Splices a user pages into a pipe.

  • Provides userspace programs with full control over an arbitrary kernel buffer

  • “Copies" data from user space into the kernel buffer.

    long vmsplice(intfd, const structiovec *iov, unsigned long nr_segs, unsigned int flags);

    Description: The vmsplice() system call maps nr_segsranges of user memory described by iov into a pipe. The file descriptor fd must refer to a pipe.

Bugs in vmsplice
Bugs in vmsplice()

  • Doesn't check whether that application had the right to write to a specific memory location. So it acts as a quick-and-easy rootkit installation mechanism.

  • Doesn’t check whether the iovec structures (memory region) passed were in readable memory.

  • The third problem is in the memory-to-pipe implementation. This is an information disclosure vulnerability.  

Vmsplice local root exploit
vmsplice() : Local Root Exploit

  • Enables non-root user to become root

  • Doesn’t need specific hardware

    Available at:



  • Allows detection of critical security vulnerabilities in short time periods for various applications.

  • Simple, efficient and can be automated.

  • Considerable speed up of the whole process of security vulnerabilities detection.

  • Downside: Not the final solution for detection of all security vulnerabilities that exist in an application.