Umberto is a library designed for mutating generic structured data (e.g., JSON, XML, X.509) and a command line application wrapping this functionality. It can apply a variety of mutations, synthesize totally new values, and apply existing mutators (e.g. Radamsa) to structure components. If you're trying to perform grammar-based fuzzing, you might find it very useful. It's probably easiest to understand by example:

echo -n "{\"a\": 1, \"b\": 2, \"c\": \"test\"}" | umberto-mutate json knuth all

    {"a":2,"c":"tesb","t":1}

echo -n "{\"a\": 1, \"b\": 2, \"c\": \"test\"}" | umberto-mutate json newvals nums

    {"a":-2.8e-20,"b":-40000,"c":"test"}

echo -n "{\"a\": 1, \"b\": 2, \"c\": \"test\"}" | umberto-mutate json radamsa strings

    {"c\u0008^\u001f":"ó �¨teï»â�¨¿st","�1�31�31�31�31�31�31�31�3â":1,"ô ó ����ó �¶Db":2}

echo -n "{\"a\": 1, \"b\": 2, \"c\": \"test\"}" | umberto-mutate string replacement all
    
    :"c2:tb{ :"{c"}t"as }c"e": "2

Umberto uses stack. Install stack, clone this repo, then run stack build && stack install. If you want to use the Radamsa fuzzer, you will also need to install it separately.

Umberto provides a simple executable, umberto-mutate, that wraps most of its functionality. Typical usage is as follows:

echo -n mydata | umberto-mutate FORMAT MUTATOR TARGET

FORMAT can be any of the following:

• json

• string (or essentially "no format")

• xml (relatively untested)

• der (X.509 DER, relatively untested)

MUTATOR can be any of the following:

• knuth: Knuth shuffle targeted values

• replacement: Replacement-shuffle targeted values

• newvals: Synthesize new targeted values in place of old ones

• radamsa: Shell out to radamsa for mutation (only works on strings)

TARGET can be any of the following:

• strings: String types

• nums: Numeric types

• all: All types

Most of the functionality of Umberto is available in lib/Umberto.hs. Mutators that make use of typeclass polymorphism require some usage of Template Haskell to violate the open world assumption. This is available in Umberto.TH but should only be used in executable code, never in libraries.