Program Environment Fuzzing (EnvFuzz)

EnvFuzz (εFuzz) is a new type of fuzzer that can fuzz just about anything, including:

• Network servers/clients
• Graphical User Interface (GUI) applications
• Editors
• Compilers
• Databases
• any other Linux user-mode software, etc.

For example, the following demo shows how to fuzz a GUI application using EnvFuzz:

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[Demo of EnvFuzz fuzzing a GUI application binary (gnome-calculator). First, the app is run normally, and all environmental interactions (including user inputs) are recorded to a file. Next, the app is fuzzed, this time by repeatedly replaying the original recording but with one or mutations applied. EnvFuzz quickly finds several crashes, as highlighted in red.]

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Unlike existing fuzzers, which only fuzz a specific input source (like AFL), EnvFuzz fuzzes the entire interaction between the subject and its environment (ε)---including all files (configuration, cache, resource, fonts, etc.), sockets (session manager, accessibility service, name service, etc.), user interactions via the windowing system, special files, devices, and standard streams, as illustrated below:

In other words, EnvFuzz considers the entire environment (ε) itself is the fuzz target---a.k.a. program environment fuzzing. This even includes user interactions via the windowing system (e.g., mouse movements, button clicks, etc.), which are treated as just another input source, no different than any other socket or file. This makes EnvFuzz a very comprehensive fuzzer, as it will automatically fuzz all inputs (and input combinations), even obscure inputs that are normally overlooked in a typical fuzz campaign.

EnvFuzz is also very general, and is designed to fuzz off-the-shelf user-mode Linux binaries with zero configuration or set-up. See the demo above.

How EnvFuzz Works?

EnvFuzz is based on an underlying full environmental Record and Replay (rr) and fuzzing infrastructure. The infrastructure is based on the insight that, for typical user-mode programs, all environmental interactions pass through the kernel-user mode interface. Thus, by recording this interface, we also implicitly record the program's interaction with the environment, which then can be subject to fuzzing. Basically, EnvFuzz works in two phases:

1. A Recording phase that executes the program normally, and records all interactions (e.g., system calls, signals, thread switches, etc.) between the subject and its environment into a file.
2. Next, a Replay-with-Fuzzing phase that repeatedly re-executes the program in a fuzzing loop. However, this time the original environmental interactions are replayed from the recording, but with one or more possible mutations applied. These mutations can induce new program behaviours and possible crashes.

Since EnvFuzz works at the abstraction of environmental interactions, it can fuzz a very diverse range of subjects without any special-case handling. This makes EnvFuzz powerful and easy-to-use.

An example of EnvFuzz usage is shown in the simple demo above:

1. The first phase records the gnome-calculator app using the command:

    $ ./env-fuzz record gnome-calculator
   

   This creates an out/ sub-directory, and the recording is stored in a out/RECORD.pcap.gz file.

2. The second phase fuzzes the gnome-calculator app using the command:

    $ ./env-fuzz fuzz
   

   The fuzzer uses the original recording from step (1.) as the initial seed, and repeatedly re-executes the program. Rather than replaying the original recording exactly, the fuzzer will apply one (or more) mutations, inducing new program behaviours and possible crashes.

Discovered crashes are stored in the out/crash/ sub-directory, and can be replayed using the command:

    $ ./env-fuzz replay out/crash/SIGSEGV_XXXX_m0YYYY.patch

We applied EnvFuzz to a diverse range of programs and discovered several new bugs, including those that are difficult or impossible to find with traditional fuzzers. For more information, please see the preprint listed below.

Building

To build EnvFuzz, simply run the build.sh script.

    $ ./build.sh

This has only been tested on Ubuntu-based systems.

EnvFuzz Usage

Record:

    $ ./env-fuzz record -- vim hello.txt

Replay:

    $ ./env-fuzz replay

Fuzz:

    $ ./env-fuzz fuzz

Replay crash:

    $ ./env-fuzz replay out/crash/SIGSEGV_XXXX_mYYYYY.patch

Debug crash:

    $ ./env-fuzz replay out/crash/SIGSEGV_XXXX_mYYYYY.patch -d

EnvFuzz also supports (optional) AFL-style coverage instrumentation:

Instrument program binary:

    $ ./env-fuzz instrument program

This will generate an instrumented program.rr binary, that can be substituted for the original.

It is also possible to instrument library code:

    $ ./env-fuzz instrument /path/to/library.so

This will place an instrumented version of the library into the lib/ sub-directory, which is included in the library search path.

EnvFuzz Files

During fuzzing, several files will be generated:

• out/COMMAND.cmd: The command-line
• out/RECORD.pcap.gz: The recording
• out/crash/*.patch: Crashing patches
• out/hang/*.patch: Hanging patches
• out/abort/*.patch: Aborting patches
• out/queue/m*/*.patch: Interesting patches
• lib/: Location where the patched libc and instrumented libraries are stored.

Note that interactions stored in the out/RECORD.pcap.gz file can be viewed using Wireshark.

EnvFuzz Technical Information

EnvFuzz uses E9Patch to statically rewrite all syscall instructions in libc.

• https://github.com/GJDuck/e9patch

Thus, whenever the program invokes a system call (e.g., open, read, write, etc.), the call will be diverted to our record-and-replay infrastructure. For recording, the infrastructure acts as a man-in-the-middle between user and kernel-mode, and all interactions are saved to a file. For replay (with fuzzing), the program is (repeatedly) executed again, but this time each system call is replayed from the original recording, possibly with one or more mutations applied. During replay, system calls are almost entirely serviced from the recording, and there is no interaction with the kernel and the real environment. In addition to libc system calls, EnvFuzz also special methods for handling the vDSO, signals, thread switches, and syscall instructions outside of libc. EnvFuzz does not use ptrace.

One problem is that program behaviour can (and will) diverge after a mutation is applied. Indeed, the main point of fuzzing is to induce new behaviours in the hope of finding new bugs. To handle this case, EnvFuzz resorts to "system call emulation" after mutation, in a "relaxed" replay-mode. This allows for diverse program behaviours to be explored using only the original recording. Please see the preprint below for more information.

EnvFuzz Status

Implementing a full environmental record and replay infrastructure is notoriously challenging. For example, the related rr-debug project estimates a total of five person-years total (source) was spent on development (as of 2017), and even then it cannot perfectly record and replay all programs. Our underlying record and eplay framework has not nearly had as much development time, and the current implementation should be viewed as a "research prototype" that will not necessarily work for all programs. Nevertheless, we provide the system "as-is", since EnvFuzz has been proven effective at finding bugs that other fuzzers cannot detect, even if the implementation is not fully polished.

We will continue to develop and improve EnvFuzz depending on the level of interest from the community.

EnvFuzz Issues

Please keep in mind that EnvFuzz is alpha-quality software and a research prototype.

Please report obvious bugs here:

• https://github.com/GJDuck/EnvFuzz/issues

Issues relating to unexpected divergence during replay should generally not be reported. That said, pull requests that fix divergence issues are very welcome.

Similarly, issues relating to missing ioctls, fcntls, and prctls should not be reported. Instead, you should update the corresponding .tab file if possible, and consider making a pull request.

Acknowledgement

This research is supported by the National Research Foundation, Singapore, and Cyber Security Agency of Singapore under its National Cybersecurity R&D Programme (Fuzz Testing NRF-NCR25-Fuzz-0001). Any opinions, findings and conclusions, or recommendations expressed in this material are those of the author(s) and do not reflect the views of National Research Foundation, Singapore, and Cyber Security Agency of Singapore.

License

This software has been released under the GNU Public License (GPL) Version 3. See the LICENSE file for more information.

Citing EnvFuzz

For more information, please see our research paper:

• Ruijie Meng, Gregory J. Duck, Abhik Roychoudhury, Program Environment Fuzzing, ACM SIGSAC Conference on Computer and Communications Security (CCS), 2024.

If you use this code in your scientific work, please cite the paper as follows:

@inproceedings{envfuzz,
    title={Program Environment Fuzzing},
    author={Meng, Ruijie and Duck, Gregory J. and Roychoudhury, Abhik},
    booktitle={Proceedings of the 31st ACM SIGSAC Conference on Computer and Communications Security (CCS)},
    year={2024}
}