Configuration Fuzzing for Software Vulnerability Detection Huning Dai, Chris Murphy, Gail Kaiser Columbia University

Observation Most vulnerabilities only reveal themselves under three conditions: 1. particular inputs Fuzz Testing (Miller et al., 1988 ) A. Randomly generated inputs may fail to satisfy syntactic constraints. B. It is hard to evaluate how much of the input/configuration space is explored C. Limited information about the "failure"

Observation Most vulnerabilities only reveal themselves under three conditions: 2. particular configurations of the software Configuration Testing (Memon and Porter et al., 2004) A. Didn’t apply to security testing. B. Provide little information other than pass/fail

Observation Most vulnerabilities only reveal themselves under three conditions: 3. particular runtime environment. Fault Injection (Hsueh et al., 1997) A. Permutes the external environment. B. Relies on the faults being injected. C. Considerable false postives.

Our Solution Configuration Fuzzing A. Instead of generating random inputs, Configuration Fuzzing mutates the application configuration. B. To increase effectiveness, Configuration Fuzzing tests are carried out “In Vivo” after a software is released, with real-world inputs and runtime environment. C. Instead of only checking for failure, surveillance functions are run throughout the tests; these functions check for violations of “security invariants” and log detailed information.

Overview Background Model ConFu Framework Case Studies Limitations and Conclusion

Background In Vivo Testing (Murphy et al., 2009) Executes tests in the context of the running program after the software is released without affecting the main process. Security Invariants (Biskup, 2009) Not merely const int security; const char secure; But rules once broken indicates …

Approach Configuration Fuzzing Configuration Fuzzing mutates the application configuration under predefined configuration constraints of the software-under-test to look for potential vulnerabilities. Surveillance functions using security invariants are executed throughout the test in order to detect vulnerabilities. Tests are executed in the deployment process while the application is running, “in vivoly”.

Model

Introduction to ConFu ConFu: CONfiguration FUzzing testing framework Steps: 1. Identifying the configuration variables 2. Generating fuzzing code 3. Identifying functions to test 4. Generating test code 5. Executing tests

STEP 1 Identifying the configuration variables X11Forwarding yes #[options.x11_forwarding]@{0,1} TCPKeepAlive yes #[options.tcp_keep_alive]@{0,1} UseLogin no #[options.use_login]@{0,1} Protocol 1 #[options.permit_root_login]@{1,2,3} … … Part of the annotated configuration file of OpenSSH

STEP 2 Generating fuzzing code An example fuzzer for OpenSSH typedef struct { int x11_forward; int tcp_keep_alive; … } result; void fuzz_config() { /* generate a set of values */ result r=covering_array(); options.x11_forward = r.x11_forward; options.tcp_keep_alive = r.tcp_keep_alive; ... } An example fuzzer for OpenSSH

STEP 3 & STEP 4 Identifying functions to test Generating test code do_child()  ConFu_do_child() Generating test code void ConFu_test_do_child(…) { fuzz_config(); /*Fuzz configuration*/ ConFu_do_child(…); /*Call the original function*/ check_invariants(); } Test function for do_child()

STEP 5 Executing tests fork() void do_child(…) { do_child(Wrapper) void do_child(…) { /*Create new process*/ int pid = fork(); if(pid == 0){ /*Test function*/ ConFu_test_do_child(…); exit(0); } /*Original function*/ return ConFu_do_child(); fork() test_do_child(test) _do_child(original) exit continue Wrapper function for do_child()

Case Studies: Feasibility Reproduce known vulnerabilities and use ConFu to detect them. CVE-2000-0525: early versions of OpenSSH do not properly drop privileges when the UseLogin option is enabled, which allow local users to execute arbitrary commands by providing the command to the ssh daemon. CVE-2009-2958: The tftp_request function in tftp.c in dnsmasq before 2.50, when --enable-tftp is used, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a TFTP read (aka RRQ) request.

Case Studies: Performance Target program: OpenSSH 2.1.0 Chosen function: do_child() Configuration: permit root login, ignore rhosts, ignore user known hosts, strict modes, x11 forwarding … a total of 15 configuration variables. Environment: Intel Core2Quad Q6600 server with 2.40GHz and 2GB of RAM running Ubuntu 8.04.3

Case Studies: Performance Results # of tests Overhead introduced by fuzz_config Per test introduced by _do_child Per test Check_invariants Per test Total Avg. Additional Time Per test 100 0.034 0.0027 0.00001 0.037 1000 0.042 0.0024 0.045 10000 0.038 0.0029 0.041 100000 0.0023 0.039 Overhead of instrumented do_child()(in seconds) with varying number of tests

Limitations and Future Work Testers’ intervention is required to identify the functions to test A priori knowledge of the potential exploitation behavior is required

Conclusion Our contribution is an approach that checks for software vulnerability after the software is released and developed a testing framework based on this approach. Useful in helping developers build more secure software and improve the security of existing software systems.

Configuration Fuzzing for Software Vulnerability Detection Huning Dai dai@cs.columbia.edu

What is Covering Array? A B C 0 0 0 0 1 1 1 0 1 1 1 0 0 0 0 0 1 1 1 0 1 1 1 0 A 2-way covering array for three variables We notice that whichever two columns out of the three columns are chosen, all possible pairs of values appear. Specifically, the pairs 00, 01, 10 and 11 all appear in the rows when we look at the columns of AB only, AC only and BC only.