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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 BiswajitMazumder RohitHooda ArpanChowdhary
Agenda • 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? • Short for FUZZ-TESTING. • Technique of Black-box testing Fuzzer Inputs: Malformed / SemiMalformed Random / Adaptive Black Box Crashes / Information leaks / Delays
Fuzzing Techniques • Event-Driven Fuzz • Character-Driven Fuzz • Database Fuzz
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 • 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 • 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 2.6.27.7 i.e. sys_getdomainname(). • Sanitize method for Local root exploit for vmsplice() syscall.
structutsname /* Structure describing the system and machine. */ structutsname { /* Name of the implementation of the operating system. */ char sysname[_UTSNAME_SYSNAME_LENGTH]; /* Name of this node on the network. */ char nodename[_UTSNAME_NODENAME_LENGTH]; /* Current release level of this implementation. */ char release[_UTSNAME_RELEASE_LENGTH]; /* Current version level of this release. */ char version[_UTSNAME_VERSION_LENGTH]; /* Name of the hardware type the system is running on. */ char machine[_UTSNAME_MACHINE_LENGTH]; /* 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. temp.mynetwork.org “mynetwork” is the domainname.
sys_getdomainname() contd… asmlinkage long sys_getdomainname(char __user *name, intlen) { intnlen; int err = -EINVAL; + if (len < 0 || len > __NEW_UTS_LEN) + goto done; down_read(&uts_sem); nlen = strlen(utsname()->domainname) + 1; if (nlen < len) len = nlen; if ( copy_to_user(name, utsname()->domainname, len) ){ err = -EFAULT; goto done; } err = 0; done: up_read(&uts_sem); return err; }
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() • 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 • Enables non-root user to become root • Doesn’t need specific hardware Available at: • http://www.milw0rm.com/exploits/5092
Conclusion • 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.
