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| -rw-r--r-- | docs/fuzzing_in_depth.md | 20 |
1 files changed, 8 insertions, 12 deletions
diff --git a/docs/fuzzing_in_depth.md b/docs/fuzzing_in_depth.md index 19d8e783..2365c6fd 100644 --- a/docs/fuzzing_in_depth.md +++ b/docs/fuzzing_in_depth.md @@ -336,22 +336,19 @@ target as possible improves the efficiency a lot. To operate correctly, the fuzzer requires one or more starting files that contain a good example of the input data normally expected by the targeted -application. There are two basic rules: +application. -- Keep the files small. Under 1 kB is ideal, although not strictly necessary. - For a discussion of why size matters, see [perf_tips.md](perf_tips.md). +Try to gather valid inputs for the target from wherever you can. E.g., if it is +the PNG picture format, try to find as many PNG files as possible, e.g., from +reported bugs, test suites, random downloads from the internet, unit test case +data - from all kind of PNG software. -- Use multiple test cases only if they are functionally different from each - other. There is no point in using fifty different vacation photos to fuzz an - image library. +If the input format is not known, you can also modify a target program to write +normal data it receives and processes to a file and use these. You can find many good examples of starting files in the [testcases/](../testcases) subdirectory that comes with this tool. -PS. If a large corpus of data is available for screening, you may want to use -the afl-cmin utility to identify a subset of functionally distinct files that -exercise different code paths in the target binary. - #### b) Making the input corpus unique Use the AFL++ tool `afl-cmin` to remove inputs from the corpus that do not @@ -787,8 +784,7 @@ Another tool in AFL++ is the afl-analyze tool. It takes an input file, attempts to sequentially flip bytes, and observes the behavior of the tested program. It then color-codes the input based on which sections appear to be critical, and which are not; while not bulletproof, it can often offer quick insights into -complex file formats. More info about its operation can be found near the end of -[technical_details.md](technical_details.md). +complex file formats. ### The End |