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69 lines
2.5 KiB
Markdown
69 lines
2.5 KiB
Markdown
What is it?
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------
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This directory contains fuzz targets.
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Fuzz targets are simple codes using the library.
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They are used with a so-called fuzz driver, which will generate inputs, try to process them with the fuzz target, and alert in case of an unwanted behavior (such as a buffer overflow for instance).
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These targets were meant to be used with oss-fuzz but can be used in other contexts.
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This code was contributed by Philippe Antoine ( Catena cyber ).
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How to run?
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------
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To run the fuzz targets like oss-fuzz:
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```
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git clone https://github.com/google/oss-fuzz
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cd oss-fuzz
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python infra/helper.py build_image mbedtls
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python infra/helper.py build_fuzzers --sanitizer address mbedtls
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python infra/helper.py run_fuzzer mbedtls fuzz_client
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```
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You can use `undefined` sanitizer as well as `address` sanitizer.
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And you can run any of the fuzz targets like `fuzz_client`.
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To run the fuzz targets without oss-fuzz, you first need to install one libFuzzingEngine (libFuzzer for instance).
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Then you need to compile the code with the compiler flags of the wished sanitizer.
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```
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perl scripts/config.pl set MBEDTLS_PLATFORM_TIME_ALT
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mkdir build
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cd build
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cmake ..
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make
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```
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Finally, you can run the targets like `./test/fuzz/fuzz_client`.
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Corpus generation for network trafic targets
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------
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These targets use network trafic as inputs :
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* client : simulates a client against (fuzzed) server traffic
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* server : simulates a server against (fuzzed) client traffic
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* dtls_client
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* dtls_server
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They also use the last bytes as configuration options.
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To generate corpus for these targets, you can do the following, not fully automated steps :
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* Build mbedtls programs ssl_server2 and ssl_client2
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* Run them one against the other with `reproducible` option turned on while capturing trafic into test.pcap
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* Extract tcp payloads, for instance with tshark : `tshark -Tfields -e tcp.dstport -e tcp.payload -r test.pcap > test.txt`
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* Run a dummy python script to output either client or server corpus file like `python dummy.py test.txt > test.cor`
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* Finally, you can add the options by appending the last bytes to the file test.cor
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Here is an example of dummy.py for extracting payload from client to server (if we used `tcp.dstport` in tshark command)
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```
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import sys
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import binascii
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f = open(sys.argv[1])
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for l in f.readlines():
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portAndPl=l.split()
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if len(portAndPl) == 2:
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# determine client or server based on port
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if portAndPl[0] == "4433":
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print(binascii.unhexlify(portAndPl[1].replace(":","")))
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```
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