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

Table of contents

Project overview: mp4parse-rust
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: avif
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Fuzzer: mp4
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
mp4parse_capi/fuzz/fuzz_targets/avif.rs
Dictionary
Fuzzer function priority
mp4parse_capi/fuzz/fuzz_targets/mp4.rs
Dictionary
Fuzzer function priority
Runtime coverage analysis
Complex functions with low coverage
Fuzz driver synthesis
New fuzzers
Files and Directories in report
Files in report
Directories in report
Function call coverage
Function in each files in report
Metadata section
Sink analyser for CWEs
Report generation date: 2026-10-17

Project overview: mp4parse-rust

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
5.0%
27 / 496
Cyclomatic complexity statically reachable by fuzzers
10.0%
153 / 1483
Runtime code coverage of functions
21.0%
102 / 496

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
avif mp4parse_capi/fuzz/fuzz_targets/avif.rs 78 485 18 9 0 42 avif.rs
mp4 mp4parse_capi/fuzz/fuzz_targets/mp4.rs 89 477 15 5 0 121 mp4.rs

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: avif

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 1905 98.0%
gold [1:9] 21 1.08%
yellow [10:29] 4 0.20%
greenyellow [30:49] 1 0.05%
lawngreen 50+ 12 0.61%
All colors 1943 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
334 1106 Track::new call site: 01106 read_trak
316 1441 BMFFBox::bytes_left call site: 01441 read_udta
230 747 UnsupportedFeatures::insert call site: 00747 read_iprp
175 512 BMFFBox::bytes_left call site: 00512 read_avif_meta
171 340 BMFFBox::box_iter call site: 00340 read_sinf
89 93 fail_with_status_if call site: 00093 fuzz_target
69 1758 UnsupportedFeatures::insert call site: 01758 fuzz_target
66 24 mp4parse_avif_new call site: 00024 fuzz_target
62 1880 UnsupportedFeatures::insert call site: 01880 fuzz_target
58 688 UnsupportedFeatures::insert call site: 00688 read_iloc
54 285 BMFFBox::bytes_left call site: 00285 BoxIter::next_box
50 998 calculate_ipma_total_associations call site: 00998 fuzz_target

Runtime coverage analysis

Covered functions
517
Functions that are reachable but not covered
69
Reachable functions
78
Percentage of reachable functions covered
11.54%
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
mp4parse_capi/fuzz/fuzz_targets/avif.rs 11
mp4parse_capi/src/lib.rs 64
mp4parse_capi/tests/test_xhe_aac.rs 7
mp4parse/src/lib.rs 306
mp4parse_capi/fuzz/fuzz_targets/mp4.rs 15
mp4parse/src/unstable.rs 18
mp4parse/tests/public.rs 12
mp4parse/src/tests.rs 24
mp4parse/src/macros.rs 2

Fuzzer: mp4

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 0 256 53.4%
gold [1:9] 1 0.20%
yellow [10:29] 1 0.20%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 221 46.1%
All colors 479 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
23 0 EP call site: 00000 mp4parse_new_common
20 257 get_indice_table call site: 00257 mp4parse_get_track_audio_info
18 201 get_track_audio_info call site: 00201 mp4parse_new_common
17 70 sample_to_chunk_iter call site: 00070 fuzz_target
17 435 mp4parse_is_fragmented call site: 00435 mp4parse_get_track_audio_info
14 342 SampleToChunkIterator::locate call site: 00342 TimeOffsetIterator::next
11 49 get_pssh_info call site: 00049 fuzz_target
11 467 mp4parse_get_pssh_info call site: 00467 mp4parse_get_track_audio_info
10 418 mp4parse_get_indice_table call site: 00418 fuzz_target
9 383 TimeOffsetIterator::next_offset_time call site: 00383 TimeOffsetIterator::next
8 96 mp4parse_get_track_info call site: 00096
7 289 get_indice_table call site: 00289 parse_minimal_mp4

Runtime coverage analysis

Covered functions
601
Functions that are reachable but not covered
46
Reachable functions
89
Percentage of reachable functions covered
48.31%
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
mp4parse_capi/fuzz/fuzz_targets/mp4.rs 16
mp4parse_capi/src/lib.rs 66
mp4parse_capi/tests/test_xhe_aac.rs 2
mp4parse/src/lib.rs 15
mp4parse/src/unstable.rs 45

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

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

Functions statically reachable by fuzzers
5.0%
27 / 496
Cyclomatic complexity statically reachable by fuzzers
10.0%
153 / 1483

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.

mp4parse_capi/fuzz/fuzz_targets/avif.rs

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=['Track::new', 'BMFFBox::bytes_left', 'UnsupportedFeatures::insert', 'BMFFBox::box_iter', 'fail_with_status_if', 'mp4parse_avif_new']

mp4parse_capi/fuzz/fuzz_targets/mp4.rs

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=['get_indice_table', 'get_track_audio_info', 'sample_to_chunk_iter', 'mp4parse_is_fragmented', 'SampleToChunkIterator::locate', 'get_pssh_info', 'mp4parse_get_pssh_info', 'mp4parse_get_indice_table', 'TimeOffsetIterator::next_offset_time']

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
mp4parse::read_audio_sample_entry::mp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::OffsetReadermp4parse_capi::Mp4parseIo 74 32 43.24%
mp4parse::read_video_sample_entry::mp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::OffsetReadermp4parse_capi::Mp4parseIo 137 58 42.33%
mp4parse::read_colr::mp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::OffsetReadermp4parse_capi::Mp4parseIo 44 17 38.63%
mp4parse::read_ilst::mp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::OffsetReadermp4parse_capi::Mp4parseIo 58 14 24.13%
mp4parse::read_iprp::mp4parse::BMFFBoxmp4parse::OffsetReadermp4parse_capi::Mp4parseIo 166 74 44.57%
mp4parse::read_stbl::mp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::BMFFBoxmp4parse::OffsetReadermp4parse_capi::Mp4parseIo 36 15 41.66%
mp4parse::read_avif::mp4parse_capi::Mp4parseIo::{closure:#7} 41 7 17.07%

Fuzz driver synthesis

New fuzzers

The below fuzzers are templates and suggestions for how to target the set of optimal functions above

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/mp4parse-rust/mp4parse/src/macros.rs ['avif'] []
/src/mp4parse-rust/mp4parse/src/lib.rs ['avif', 'mp4'] ['avif', 'mp4']
/src/mp4parse-rust/mp4parse_capi/tests/test_afconvert.rs [] []
/src/mp4parse-rust/mp4parse_capi/tests/test_sample_table.rs [] []
/src/mp4parse-rust/mp4parse_capi/tests/test_encryption.rs [] []
/src/mp4parse-rust/mp4parse_capi/fuzz/fuzz_targets/mp4.rs ['avif', 'mp4'] []
/src/mp4parse-rust/mp4parse_capi/tests/test_avis.rs [] []
/src/mp4parse-rust/mp4parse/tests/overflow.rs [] []
/src/mp4parse-rust/mp4parse/src/tests.rs ['avif'] []
/src/mp4parse-rust/mp4parse_capi/tests/test_fragment.rs [] []
/src/mp4parse-rust/mp4parse_capi/src/lib.rs ['avif', 'mp4'] ['avif', 'mp4']
/src/mp4parse-rust/mp4parse_capi/tests/test_xhe_aac.rs ['avif', 'mp4'] []
/src/mp4parse-rust/mp4parse_capi/examples/dump.rs [] []
/src/mp4parse-rust/mp4parse_capi/tests/test_workaround_stsc.rs [] []
/src/mp4parse-rust/mp4parse/src/boxes.rs [] []
/src/mp4parse-rust/mp4parse/benches/avif_benchmark.rs [] []
/src/mp4parse-rust/mp4parse/tests/public.rs ['avif'] []
/src/mp4parse-rust/mp4parse_capi/tests/test_rotation.rs [] []
/src/mp4parse-rust/mp4parse/src/unstable.rs ['avif', 'mp4'] ['avif', 'mp4']
/src/mp4parse-rust/mp4parse_capi/tests/test_colour_info.rs [] []
/src/mp4parse-rust/mp4parse_capi/tests/test_chunk_out_of_range.rs [] []
/src/mp4parse-rust/mp4parse_capi/fuzz/fuzz_targets/avif.rs ['avif'] ['avif']

Directories in report

Directory
/src/mp4parse-rust/mp4parse_capi/examples/
/src/mp4parse-rust/mp4parse_capi/src/
/src/mp4parse-rust/mp4parse_capi/tests/
/src/mp4parse-rust/mp4parse/benches/
/src/mp4parse-rust/mp4parse/tests/
/src/mp4parse-rust/mp4parse/src/
/src/mp4parse-rust/mp4parse_capi/fuzz/fuzz_targets/

Function call coverage

This section shows a list of 3rd party function calls and their relative coverage information. By static analysis of the target project code, all of the 3rd party function call and their caller information, including the source file and line number that initiate the call are captured. The caller source code file and line number are shown in column 2 while column 1 is the function name of the 3rd party function call. Each occurrent of the 3rd party function call will occuply a separate row. Column 3 of each row indicate if the 3rd party call in the source file line is unreachable. Column 4 lists all fuzzers that have covered that particular system call in that specific location (source file and line)during their dynamic fuzzing.

Function in each files in report

Target sink Callsite location Reached by fuzzer Covered by Fuzzers

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
avif fuzzerLogFile-avif.data fuzzerLogFile-avif.data.yaml avif.covreport
mp4 fuzzerLogFile-mp4.data fuzzerLogFile-mp4.data.yaml mp4.covreport

Sink analyser for CWEs

No sink functions/methods found in the target project.