Fuzz introspector
For issues and ideas: https://github.com/ossf/fuzz-introspector/issues
Project coverage
Per-fuzzer coverage

Table of contents

Project overview: njs
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: njs_process_script_fuzzer
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Analyses and suggestions
Optimal target analysis
Remaining optimal interesting functions
All functions overview
Fuzz engine guidance
external/njs_shell.c
Dictionary
Fuzzer function priority
Runtime coverage analysis
Complex functions with low coverage
Files and Directories in report
Files in report
Directories in report
Metadata section
Report generation date: 2026-05-18

Project overview: njs

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
22.0%
329 / 1482
Cyclomatic complexity statically reachable by fuzzers
26.0%
3970 / 15243
Runtime code coverage of functions
70.0%
1041 / 1482

Warning: The number of runtime covered functions are larger than the number of reachable functions. This means that Fuzz Introspector found there are more functions covered at runtime than what is considered reachable based on the static analysis. This is a limitation in the analysis as anything covered at runtime is by definition reachable by the fuzzers.
This is likely due to a limitation in the static analysis. In this case, the count of functions covered at runtime is the true value, which means this is what should be considered "achieved" by the fuzzer.

Use the project functions table below to query all functions that were not covered at runtime.

Fuzzers overview

Fuzzer Fuzzer filename Functions Reached Functions unreached Fuzzer depth Files reached Basic blocks reached Cyclomatic complexity Details
njs_process_script_fuzzer external/njs_shell.c 356 1347 25 39 11175 4026 njs_shell.c

Project functions overview

The following table shows data about each function in the project. The functions included in this table correspond to all functions that exist in the executables of the fuzzers. As such, there may be functions that are from third-party libraries.

For further technical details on the meaning of columns in the below table, please see the Glossary .

Func name Functions filename Args Function call depth Reached by Fuzzers Runtime reached by Fuzzers Combined reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Fuzzer details

Fuzzer: njs_process_script_fuzzer

Call tree

The calltree shows the control flow of the fuzzer. This is overlaid with coverage information to display how much of the potential code a fuzzer can reach is in fact covered at runtime. In the following there is a link to a detailed calltree visualisation as well as a bitmap showing a high-level view of the calltree. For further information about these topics please see the glossary for full calltree and calltree overview

Full calltree

Call tree overview bitmap:

The distribution of callsites in terms of coloring is
Color Runtime hitcount Callsite count Percentage
red 0 290 23.1%
gold [1:9] 1 0.07%
yellow [10:29] 2 0.15%
greenyellow [30:49] 3 0.23%
lawngreen 50+ 959 76.4%
All colors 1255 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
22 1232 njs_main call site: 01232 njs_process_file
20 357 njs_engine_njs_init call site: 00357 njs_vm_compile_module
10 761 njs_object_enumerate_string call site: 00761 njs_array_alloc
9 341 njs_scope_global_index call site: 00341 njs_rejection_tracker
9 804 njs_get_own_ordered_keys call site: 00804 njs_value_property
9 915 njs_object_own_enumerate call site: 00915 njs_value_property
7 982 njs_object_prop_define call site: 00982 njs_typed_array_set_value
7 1196 njs_lexer_in_stack_push call site: 01196 njs_parser_export_sink
7 1224 njs_generate_scope call site: 01224 njs_throw_error
6 1 LLVMFuzzerTestOneInput call site: 00001 njs_dprintf
5 528 njs_function_lambda_call call site: 00528 njs_throw_error
4 105 njs_error_alloc call site: 00105 njs_throw_error

Runtime coverage analysis

Covered functions
1244
Functions that are reachable but not covered
47
Reachable functions
356
Percentage of reachable functions covered
86.8%
NB: The sum of covered functions and functions that are reachable but not covered need not be equal to Reachable functions . This is because the reachability analysis is an approximation and thus at runtime some functions may be covered that are not included in the reachability analysis. This is a limitation of our static analysis capabilities.
Warning: The number of covered functions are larger than the number of reachable functions. This means that there are more functions covered at runtime than are extracted using static analysis. This is likely a result of the static analysis component failing to extract the right call graph or the coverage runtime being compiled with sanitizers in code that the static analysis has not analysed. This can happen if lto/gold is not used in all places that coverage instrumentation is used.
Function name source code lines source lines hit percentage hit

Files reached

filename functions hit
external/njs_shell.c 16
src/njs_sprintf.c 5
src/njs_rbtree.c 6
src/njs_mp.c 15
src/njs_malloc.c 2
src/njs_vm.c 17
src/njs_regexp.c 6
external/njs_regex.c 8
src/njs_error.c 8
src/njs_builtin.c 2
src/njs_atom.c 4
src/njs_flathsh.c 11
src/njs_string.c 20
src/njs_utf8.c 5
src/njs_djb_hash.c 1
src/njs_trace.c 1
src/njs_object.c 15
src/njs_dtoa.c 35
src/njs_cutils.h 8
src/njs_number.c 2
src/njs_arr.c 4
src/njs_function.c 18
src/njs_symbol.c 3
src/njs_scope.c 2
src/njs_value.c 17
src/njs_module.c 2
src/njs_variable.c 6
src/njs_parser.c 7
src/njs_lexer.c 11
src/njs_object_prop.c 7
src/njs_async.c 1
src/njs_promise.c 5
src/njs_array.c 11
src/njs_vmcode.c 29
src/njs_utils.c 2
src/njs_typed_array.c 3
src/njs_array_buffer.c 1
src/njs_chb.c 7
src/njs_generator.c 7

Analyses and suggestions

Optimal target analysis

Remaining optimal interesting functions

The following table shows a list of functions that are optimal targets. Optimal targets are identified by finding the functions that in combination, yield a high code coverage.

Func name Functions filename Arg count Args Function depth hitcount instr count bb count cyclomatic complexity Reachable functions Incoming references total cyclomatic complexity Unreached complexity
njs_generate /src/njs/src/njs_generator.c 3 ['N/A', 'N/A', 'N/A'] 40 0 1044 141 7 362 0 4211 753
njs_ext_unwrap_key /src/njs/external/njs_webcrypto_module.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 42 0 407 58 24 379 0 4051 731
njs_date_constructor /src/njs/src/njs_date.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 36 0 634 73 28 260 0 3596 279
njs_engine_njs_process_events /src/njs/external/njs_shell.c 1 ['N/A'] 20 0 142 17 6 278 0 3637 275
njs_regexp_prototype_symbol_replace /src/njs/src/njs_regexp.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 37 0 2201 268 96 272 0 3604 249
njs_fs_readlink /src/njs/external/njs_fs_module.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 43 0 346 56 21 280 0 3610 228
njs_parser_property_definition /src/njs/src/njs_parser.c 3 ['N/A', 'N/A', 'N/A'] 40 0 2457 252 87 287 0 3740 213
njs_ext_wrap_key /src/njs/external/njs_webcrypto_module.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 42 0 295 40 17 369 0 3860 201
njs_engine_njs_eval /src/njs/external/njs_shell.c 2 ['N/A', 'N/A'] 15 0 68 9 4 305 0 3853 199
njs_json_stringify /src/njs/src/njs_json.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 49 0 693 98 34 258 0 3503 147

Implementing fuzzers that target the above functions will improve reachability such that it becomes:

Functions statically reachable by fuzzers
40.0%
593 / 1482
Cyclomatic complexity statically reachable by fuzzers
46.0%
7047 / 15243

All functions overview

If you implement fuzzers for these functions, the status of all functions in the project will be:

Func name Functions filename Args Function call depth Reached by Fuzzers Runtime reached by Fuzzers Combined reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Fuzz engine guidance

This sections provides heuristics that can be used as input to a fuzz engine when running a given fuzz target. The current focus is on providing input that is usable by libFuzzer.

external/njs_shell.c

Dictionary

Use this with the libFuzzer -dict=DICT.file flag


Fuzzer function priority

Use one of these functions as input to libfuzzer with flag: -focus_function name 

-focus_function=['njs_main', 'njs_engine_njs_init', 'njs_object_enumerate_string', 'njs_scope_global_index', 'njs_get_own_ordered_keys', 'njs_object_own_enumerate', 'njs_object_prop_define', 'njs_lexer_in_stack_push', 'njs_generate_scope', 'LLVMFuzzerTestOneInput']

Runtime coverage analysis

This section shows analysis of runtime coverage data.

For futher technical details on how this section is generated, please see the Glossary .

Complex functions with low coverage

Func name Function total lines Lines covered at runtime percentage covered Reached by fuzzers
njs_array_prototype_push 47 22 46.80% ['njs_process_script_fuzzer']
njs_array_prototype_slice_copy 100 50 50.0% ['njs_process_script_fuzzer']
njs_buffer_from_object 62 29 46.77% ['njs_process_script_fuzzer']
njs_dtoa_max_len 39 20 51.28% ['njs_process_script_fuzzer']
njs_error_alloc 71 38 53.52% ['njs_process_script_fuzzer']
njs_function_capture_global_closures 42 10 23.80% ['njs_process_script_fuzzer']
njs_object_iterate_reverse 124 67 54.03% ['njs_process_script_fuzzer']
njs_json_stringify_array 65 15 23.07% ['njs_process_script_fuzzer']
njs_object_math_func 143 62 43.35% ['njs_process_script_fuzzer']
njs_module_find 44 15 34.09% ['njs_process_script_fuzzer']
njs_object_enumerate_array 62 27 43.54% ['njs_process_script_fuzzer']
njs_object_enumerate_typed_array 47 22 46.80% ['njs_process_script_fuzzer']
njs_object_enumerate_string 93 23 24.73% ['njs_process_script_fuzzer']
njs_object_own_enumerate_object 49 14 28.57% ['njs_process_script_fuzzer']
njs_parser_export 73 8 10.95% ['njs_process_script_fuzzer']
njs_parser_import 62 28 45.16% ['njs_process_script_fuzzer']
njs_vsprintf 257 128 49.80% ['njs_process_script_fuzzer']
njs_typed_array_prototype_iterator 146 73 50.0% ['njs_process_script_fuzzer']
njs_value_own_enumerate 66 11 16.66% ['njs_process_script_fuzzer']

Files and Directories in report

This section shows which files and directories are considered in this report. The main reason for showing this is fuzz introspector may include more code in the reasoning than is desired. This section helps identify if too many files/directories are included, e.g. third party code, which may be irrelevant for the threat model. In the event too much is included, fuzz introspector supports a configuration file that can exclude data from the report. See the following link for more information on how to create a config file: link

Files in report

Source file Reached by Covered by
[] []
/src/njs/src/njs_utils.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_string.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_generator.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_symbol.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_typed_array.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_promise.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_async.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_utf8.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_utf16.c [] []
/src/njs/external/njs_fs_module.c [] []
/src/njs/src/njs_module.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_shell.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_query_string_module.c [] []
/src/njs/external/njs_crypto_module.c [] []
/src/njs/src/njs_scope.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_extern.c [] []
/src/njs/src/njs_value.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_flathsh.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_regexp.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_arr.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_lexer.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_rbtree.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_chb.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_cutils.h ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_webcrypto_module.c [] []
/src/njs/src/njs_utils.h [] []
/src/njs/src/njs_malloc.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_zlib_module.c [] []
/src/njs/src/njs_str.c [] []
/src/njs/src/njs_variable.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_regex.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_boolean.c [] []
/src/njs/src/njs_encoding.c [] []
/src/njs/src/njs_number.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_builtin.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_parser.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_error.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_function.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_mp.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_djb_hash.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_math.c [] []
/src/njs/src/njs_vm.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_array_buffer.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_object_prop.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_json.c [] []
/src/njs/src/njs_buffer.c [] []
/src/njs/src/njs_disassembler.c [] []
/src/njs/src/njs_object.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_array.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_trace.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_atom.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_random.c [] []
/src/njs/src/njs_sprintf.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_iterator.c [] []
/src/njs/src/njs_dtoa.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_date.c [] []
/src/njs/src/njs_vmcode.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']

Directories in report

Directory
/src/njs/src/
/src/njs/external/

Metadata section

This sections shows the raw data that is used to produce this report. This is mainly used for further processing and developer debugging.

Fuzzer Calltree file Program data file Coverage file
njs_process_script_fuzzer fuzzerLogFile-0-hD1HXpfVsM.data fuzzerLogFile-0-hD1HXpfVsM.data.yaml njs_process_script_fuzzer.covreport