tree: 4e49860415d9b13258bf010132fdc977f60a817b [path history] [tgz]
  1. Makefile
  3. libclose.c
  4. terminal-test.c

Fuzzing terminal emulators

Step 1: Prepare and terminal-test

$ cd /home/jagger/src/honggfuzz/examples/terminal-emulators/
$ make
../../hfuzz_cc/hfuzz-clang -std=c99  -o terminal-test terminal-test.c
cc -std=c99  -shared -o libclose.c serves one purpose only: when preloaded (with it will prevent file-descriptors 1022 and 1023 (used by honggfuzz for coverage feedback accumulation) will not be closed by the fuzzed binary (terminal emulator) before passing to the terminal-test binary.

The terminal-test program will feed the terminal emulator with data from the fuzzing engine, and will try to read back any data that the terminal can produce. See the Bonus: term.log secion on why it might matter.

Step 2: Instrument your terminal emulator

Add compiler-time instrumentation to your fuzzed terminal emulator. Typically it would consist of the following sequence of commands (for xterm):

$ cd xterm-327
$ CC=/home/jagger/src/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$CC ./configure
$ CC=/home/jagger/src/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$CC make -j4

Alternatively, you might want to compile it with ASAN enabled, for better detection of memory corruption problems

$ cd xterm-327
$ HFUZZ_CC_ASAN=1 CC=/home/jagger/src/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$CC ./configure
$ HFUZZ_CC_ASAN=1 CC=/home/jagger/src/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$CC make -j4

Step 3: Create initial input corpus

It can consist even of a single file.

$ mkdir IN
$ echo A >IN/1

Step 4: Launch it!

$ /home/jagger/src/honggfuzz/honggfuzz -z -P -f IN/ -E LD_PRELOAD=/home/jagger/src/honggfuzz/examples/terminal-emulators/ -- xterm-327/xterm -e /home/jagger/src/honggfuzz/examples/terminal-emulators/terminal-test

Typical output:

----------------------------[ honggfuzz v1.0alpha ]---------------------------
  Iterations : 4,865,546 [4.87M]
       Phase : Dynamic Main (2/2)
    Run Time : 0 hrs 0 min 15 sec
   Input Dir : [865] 'IN/'
  Fuzzed Cmd : './xterm -e /home/jagger/src/honggfuzz/examples/terminal-em...'
     Threads : 4, CPUs: 8, CPU: 733% (91%/CPU)
       Speed : 320,951/sec (avg: 324,369)
     Crashes : 0 (unique: 0, blacklist: 0, verified: 0)
    Timeouts : 0 [10 sec.]
 Corpus Size : 265, max file size: 1,024
    Coverage : bb: 850 cmp: 35,516
-----------------------------------[ LOGS ]-----------------------------------
NEW, size:912 (i,b,sw,hw,cmp): 0/0/1/0/1, Tot:0/0/772/0/32216
NEW, size:940 (i,b,sw,hw,cmp): 0/0/1/0/32, Tot:0/0/773/0/32248
NEW, size:919 (i,b,sw,hw,cmp): 0/0/0/0/9, Tot:0/0/773/0/32257
NEW, size:1024 (i,b,sw,hw,cmp): 0/0/0/0/2, Tot:0/0/773/0/32259
NEW, size:1013 (i,b,sw,hw,cmp): 0/0/0/0/1, Tot:0/0/773/0/32260

Bonus: term.log

The term.log file will contain interesting data which can be fetched from the terminal emulator‘s input buffer. It will typically contains responses to ESC sequences requesting info about terminal size, or about the current color map. But, if you notice there arbitrary or binary data, basically something that a typical terminal shouldn’t responsd with, try to investigate it. You might have just found and interesting case of RCE, where arbitrary data can be pushed into terminal's input buffer, and then read back (and potentially executed) with whatever runs under said emulator (e.g. /bin/bash)