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: 2025-08-29

Project overview: njs

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
20.0%
285 / 1409
Cyclomatic complexity statically reachable by fuzzers
25.0%
3783 / 15029
Runtime code coverage of functions
36.0%
502 / 1409

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 313 1300 25 39 10782 3840 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 0 730 61.7%
gold [1:9] 73 6.17%
yellow [10:29] 29 2.45%
greenyellow [30:49] 66 5.58%
lawngreen 50+ 284 24.0%
All colors 1182 100

Fuzz blockers

The followings are the branches where fuzzer fails to bypass.

Unique non-covered Complexity Unique Reachable Complexities Unique Reachable Functions All non-covered Complexity All Reachable Complexity Function Name Function Callsite Blocked Branch
79806 344799 55 :

['njs_throw_cannot_property', 'njs_vmcode_import', 'njs_primitive_values_compare', 'njs_string_concat', 'njs_string_new', 'njs_vmcode_try_break', 'pow', 'njs_mp_alloc', 'njs_symbol_descriptive_string', 'njs_vmcode_instance_of', 'njs_vmcode_property_foreach', 'njs_value_property', 'njs_throw_error', 'njs_vm_scopes_restore', 'njs_value_property_delete', 'njs_type_string', 'njs_string_to_number', 'njs_vmcode_array', 'njs_memory_error', 'njs_function_frame_invoke', 'fmod', 'njs_vmcode_property_init', 'njs_function_name_set', 'njs_vmcode_error', 'njs_vmcode_function', 'njs_vmcode_object', 'njs_vmcode_property_in', 'njs_vmcode_try_start', 'njs_values_equal', 'njs_vm_throw', 'njs_symbol_conversion_failed', 'njs_vmcode_try_end', 'njs_dtoa', 'njs_vmcode_template_literal', 'njs_vmcode_proto_init', 'njs_value_to_string', 'njs_vmcode_arguments', 'njs_vm_exception', 'njs_vmcode_try_continue', 'njs_vmcode_typeof', 'njs_vmcode_regexp', 'njs_vmcode_return', 'njs_value_to_primitive', 'njs_value_property_set', 'njs_object_to_string', 'njs_string_eq', 'njs_vmcode_await', 'njs_vmcode_finally', 'njs_error_stack_attach', 'njs_atom_atomize_key', 'njs_mp_free', 'njs_function_frame_create', 'njs_vmcode_debugger', 'njs_object_prop_define', 'njs_primitive_value_to_string']

79806 344799 njs_vmcode_interpreter call site: 01065 /src/njs/src/njs_vmcode.c:1868
6604 6629 3 :

['njs_rbtree_delete', 'njs_vm_invoke', 'njs_engine_njs_output']

6604 6631 njs_engine_njs_process_events call site: 00000 /src/njs/external/njs_shell.c:1627
3824 3824 1 :

['njs_process_file']

3824 3824 njs_main call site: 00017 /src/njs/external/njs_shell.c:448
3482 3482 3 :

['njs_vm_value_to_string', 'njs_vm_error2', 'njs_arr_destroy']

3482 3482 njs_engine_njs_unhandled_rejection call site: 00000 /src/njs/external/njs_shell.c:1667
3195 3195 1 :

['njs_parser_export_sink']

3195 3195 njs_parser call site: 01125 /src/njs/src/njs_parser.c:612
3136 3136 1 :

['njs_vm_call']

3136 3136 njs_vm_execute_pending_job call site: 00000 /src/njs/src/njs_vm.c:711
3134 3134 1 :

['njs_async_function_frame_invoke']

3134 3134 njs_function_frame_invoke call site: 00343 /src/njs/src/njs_function.c:663
3134 3134 1 :

['njs_function_lambda_call']

3134 3134 njs_function_frame_invoke call site: 00344 /src/njs/src/njs_function.c:669
615 1078 7 :

['njs_array_add', 'njs_flathsh_each', 'njs_object_exist_in_proto', 'njs_string_new', 'njs_string_to_index', 'njs_dtoa', 'njs_flathsh_unique_find']

615 1455 njs_get_own_ordered_keys call site: 00724 /src/njs/src/njs_object.c:1019
558 558 3 :

['njs_string_index', 'njs_regexp_exec_result', 'njs_regex_capture']

558 3704 njs_regexp_builtin_exec call site: 00000 /src/njs/src/njs_regexp.c:928
329 7279 5 :

['njs_dtoa', 'njs_value_to_string', 'njs_symbol_descriptive_string', 'njs_string_new', 'njs_parser_lexer_error']

329 7279 njs_variable_scope_find call site: 00324 /src/njs/src/njs_variable.c:176
329 7279 5 :

['njs_dtoa', 'njs_value_to_string', 'njs_symbol_descriptive_string', 'njs_string_new', 'njs_parser_lexer_error']

329 7279 njs_variable_scope_find call site: 00324 /src/njs/src/njs_variable.c:215

Runtime coverage analysis

Covered functions
630
Functions that are reachable but not covered
116
Reachable functions
313
Percentage of reachable functions covered
62.94%
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 17
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 1
src/njs_diyfp.c 2
src/njs_number.c 6
src/njs_strtod.c 4
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_generator.c 5

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 1039 133 7 298 0 3865 602
njs_ext_import_key /src/njs/external/njs_webcrypto_module.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 42 0 1123 165 52 286 0 3597 460
njs_engine_njs_process_events /src/njs/external/njs_shell.c 1 ['N/A'] 21 0 150 17 6 245 0 3478 299
njs_date_constructor /src/njs/src/njs_date.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 36 0 678 73 28 220 0 3413 279
njs_regexp_prototype_symbol_replace /src/njs/src/njs_regexp.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 37 0 2298 268 96 236 0 3446 274
njs_fs_readlink /src/njs/external/njs_fs_module.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 43 0 363 56 21 240 0 3427 234
njs_parser_property_definition /src/njs/src/njs_parser.c 3 ['N/A', 'N/A', 'N/A'] 43 0 2715 252 87 245 0 3549 205
njs_engine_njs_eval /src/njs/external/njs_shell.c 2 ['N/A', 'N/A'] 16 0 73 9 4 269 0 3682 198
njs_ext_export_key /src/njs/external/njs_webcrypto_module.c 5 ['N/A', 'N/A', 'int', 'size_t', 'N/A'] 42 0 514 70 21 276 0 3419 182
njs_error_prototype_stack /src/njs/src/njs_error.c 6 ['N/A', 'N/A', 'int', 'N/A', 'N/A', 'N/A'] 37 0 477 56 21 225 0 3351 165

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

Functions statically reachable by fuzzers
37.0%
521 / 1409
Cyclomatic complexity statically reachable by fuzzers
44.0%
6559 / 15029

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_vmcode_interpreter', 'njs_value_property_set', 'njs_engine_njs_init', 'njs_main', 'njs_array_destroy', 'njs_object_value_alloc', 'njs_regexp_alloc', 'njs_vmcode_property_init']

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_regex_escape 73 18 24.65% ['njs_process_script_fuzzer']
njs_regex_compile 77 30 38.96% ['njs_process_script_fuzzer']
njs_atom_atomize_key 57 25 43.85% ['njs_process_script_fuzzer']
njs_top_level_constructor 32 12 37.5% ['njs_process_script_fuzzer']
njs_chb_drop 35 9 25.71% ['njs_process_script_fuzzer']
njs_dtoa_format 36 19 52.77%
njs_error_alloc 72 38 52.77% ['njs_process_script_fuzzer']
njs_generate_return_statement_end 58 24 41.37% ['njs_process_script_fuzzer']
njs_generate_try_left 90 39 43.33% ['njs_process_script_fuzzer']
njs_generate_try_catch 60 17 28.33% ['njs_process_script_fuzzer']
njs_lexer_number 57 25 43.85% ['njs_process_script_fuzzer']
njs_lexer_division 40 20 50.0% ['njs_process_script_fuzzer']
njs_object_enumerate_string 96 24 25.0% ['njs_process_script_fuzzer']
njs_object_own_enumerate_object 49 14 28.57% ['njs_process_script_fuzzer']
njs_get_own_ordered_keys 144 60 41.66% ['njs_process_script_fuzzer']
njs_parser_formal_parameters 56 28 50.0% ['njs_process_script_fuzzer']
njs_parser_match_arrow_expression 59 22 37.28% ['njs_process_script_fuzzer']
njs_parser_left_hand_side_expression 32 9 28.12% ['njs_process_script_fuzzer']
njs_parser_primary_expression_test 184 92 50.0% ['njs_process_script_fuzzer']
njs_parser_escape_string_create 169 58 34.31% ['njs_process_script_fuzzer']
njs_parser_escape_string_calc_length 107 38 35.51% ['njs_process_script_fuzzer']
njs_parser_regexp_literal 77 32 41.55% ['njs_process_script_fuzzer']
njs_parser_reference 87 45 51.72% ['njs_process_script_fuzzer']
njs_parser_optional_chain_after 36 13 36.11% ['njs_process_script_fuzzer']
njs_parser_unary_expression_next 43 22 51.16% ['njs_process_script_fuzzer']
njs_parser_coalesce_expression 31 8 25.80% ['njs_process_script_fuzzer']
njs_parser_assignment_operator 85 35 41.17% ['njs_process_script_fuzzer']
njs_parser_statement_wo_node 67 30 44.77% ['njs_process_script_fuzzer']
njs_parser_iteration_statement_for_map 77 35 45.45% ['njs_process_script_fuzzer']
njs_parser_for_var_binding_or_var_list 76 41 53.94% ['njs_process_script_fuzzer']
njs_parser_for_expression_map_continue 39 21 53.84% ['njs_process_script_fuzzer']
njs_parser_catch_or_finally 67 30 44.77% ['njs_process_script_fuzzer']
njs_parser_expression_statement 49 12 24.48% ['njs_process_script_fuzzer']
njs_regexp_exec 41 19 46.34% ['njs_process_script_fuzzer']
njs_regexp_prototype_symbol_split 194 82 42.26% ['njs_process_script_fuzzer']
njs_vsprintf 257 85 33.07% ['njs_process_script_fuzzer']
njs_string_prototype_concat 118 43 36.44% ['njs_process_script_fuzzer']
njs_string_trim 85 39 45.88% ['njs_process_script_fuzzer']
njs_string_prototype_split 111 28 25.22% ['njs_process_script_fuzzer']
njs_utf8_is_whitespace 32 6 18.75%
njs_qsort 63 9 14.28% ['njs_process_script_fuzzer']
njs_type_string 37 7 18.91% ['njs_process_script_fuzzer']
njs_value_property_set 164 56 34.14% ['njs_process_script_fuzzer']
njs_value_species_constructor 33 17 51.51% ['njs_process_script_fuzzer']
njs_array_property_query 85 15 17.64% ['njs_process_script_fuzzer']
njs_variable_scope_find 75 40 53.33% ['njs_process_script_fuzzer']
njs_vmcode_interpreter 1264 418 33.06% ['njs_process_script_fuzzer']
njs_vmcode_property_init 77 31 40.25% ['njs_process_script_fuzzer']
njs_function_frame_create 45 15 33.33% ['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_module.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_extern.c [] []
/src/njs/src/njs_rbtree.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_vm.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_typed_array.c ['njs_process_script_fuzzer'] []
/src/njs/src/njs_iterator.c [] []
/src/njs/src/njs_buffer.c [] []
/src/njs/src/njs_strtod.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_variable.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_fs_module.c [] []
/src/njs/external/njs_query_string_module.c [] []
/src/njs/src/njs_utils.h [] []
/src/njs/src/njs_math.c [] []
/src/njs/external/njs_sha2.c [] []
/src/njs/src/njs_json.c [] []
/src/njs/src/njs_number.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_object.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_date.c [] []
/src/njs/src/njs_dtoa.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_utils.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_sha1.c [] []
/src/njs/src/njs_utf16.c [] []
/src/njs/external/njs_zlib_module.c [] []
/src/njs/src/njs_disassembler.c [] []
/src/njs/src/njs_vmcode.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_function.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_md5.c [] []
/src/njs/src/njs_encoding.c [] []
/src/njs/src/njs_scope.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_diyfp.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_chb.c [] []
/src/njs/src/njs_malloc.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_sprintf.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_promise.c ['njs_process_script_fuzzer'] []
/src/njs/src/njs_lexer.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_arr.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_webcrypto_module.c [] []
/src/njs/src/njs_atom.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_string.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_dtoa_fixed.c [] []
/src/njs/src/njs_boolean.c [] []
/src/njs/src/njs_random.c [] []
/src/njs/src/njs_async.c ['njs_process_script_fuzzer'] []
/src/njs/src/njs_trace.c ['njs_process_script_fuzzer'] []
/src/njs/src/njs_error.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/external/njs_crypto_module.c [] []
/src/njs/src/njs_symbol.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_str.c [] []
/src/njs/src/njs_builtin.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_array.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/src/njs/src/njs_array_buffer.c ['njs_process_script_fuzzer'] []
/src/njs/src/njs_utf8.c ['njs_process_script_fuzzer'] ['njs_process_script_fuzzer']
/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']

Directories in report

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

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-p5xdpxjkx8.data fuzzerLogFile-0-p5xdpxjkx8.data.yaml njs_process_script_fuzzer.covreport