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

Table of contents

Project overview: mongoose
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: fuzz
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
test/fuzz.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: 2026-10-16

Project overview: mongoose

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
45.0%
230 / 516
Cyclomatic complexity statically reachable by fuzzers
53.0%
1914 / 3584
Runtime code coverage of functions
36.0%
184 / 516

Fuzzers overview

Fuzzer Fuzzer filename Functions Reached Functions unreached Fuzzer depth Files reached Basic blocks reached Cyclomatic complexity Details
fuzz test/fuzz.c 381 303 14 25 5024 2029 fuzz.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: fuzz

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 0 689 90.4%
gold [1:9] 0 0.0%
yellow [10:29] 4 0.52%
greenyellow [30:49] 3 0.39%
lawngreen 50+ 66 8.66%
All colors 762 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
362 170 LLVMFuzzerTestOneInput call site: 00170 mg_connect
96 574 fn(mg_connection*, int, void*) call site: 00574 mg_http_serve_file
89 672 LLVMFuzzerTestOneInput call site: 00672 mg_mgr_poll
39 533 LLVMFuzzerTestOneInput call site: 00533 mg_connect_svc
35 15 LLVMFuzzerTestOneInput call site: 00015 mg_http_get_header
12 1 LLVMFuzzerTestOneInput call site: 00001 mg_dns_parse_rr
12 58 LLVMFuzzerTestOneInput call site: 00058 mg_url_decode
10 139 LLVMFuzzerTestOneInput call site: 00139 mg_random
9 121 LLVMFuzzerTestOneInput call site: 00121 memcmp
7 107 LLVMFuzzerTestOneInput call site: 00107 mg_base64_final
6 92 LLVMFuzzerTestOneInput call site: 00092 mg_millis
5 100 LLVMFuzzerTestOneInput call site: 00100

Runtime coverage analysis

Covered functions
185
Functions that are reachable but not covered
159
Reachable functions
381
Percentage of reachable functions covered
58.27%
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.
Function name source code lines source lines hit percentage hit

Files reached

filename functions hit
test/fuzz.c 4
src/dns.c 14
src/util.c 9
src/http.c 30
src/str.c 9
src/mqtt.c 4
src/sntp.c 2
src/base64.c 7
src/json.c 5
src/net.c 16
src/tls_dummy.c 8
src/net_builtin.c 68
src/l2.c 7
src/event.c 2
src/printf.c 13
src/fmt.c 9
src/iobuf.c 5
src/url.c 4
src/log.c 4
src/ssi.c 1
src/fs.c 2
src/timer.c 3
src/ota.c 1
src/mdash.c 1
src/queue.c 3

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
mg_dash_ev_handler /src/mongoose/src/dash.c 3 ['N/A', 'int', 'N/A'] 19 0 993 119 42 239 0 1376 429
mdns_cb(mg_connection*,int,void*) /src/mongoose/src/dns.c 3 ['N/A', 'int', 'N/A'] 13 0 238 42 13 111 0 464 142
mg_l2_pppoe_rx(mg_tcpip_if*,mg_l2proto*,mg_str*,mg_str*) /src/mongoose/src/l2_ppp.c 4 ['N/A', 'N/A', 'N/A', 'N/A'] 7 0 368 58 20 56 0 141 106
mg_mqtt_connect /src/mongoose/src/mqtt.c 5 ['N/A', 'N/A', 'N/A', 'N/A', 'N/A'] 18 0 54 9 4 151 0 612 85
mg_ota_url_check /src/mongoose/src/ota.c 3 ['N/A', 'N/A', 'N/A'] 20 0 96 17 6 196 0 1052 61
mg_jwt_verify_hs256 /src/mongoose/src/jwt.c 5 ['N/A', 'size_t', 'N/A', 'N/A', 'size_t'] 7 0 108 13 6 37 0 277 57
modbus_ev_handler(mg_connection*,int,void*) /src/mongoose/src/modbus.c 3 ['N/A', 'int', 'N/A'] 11 0 141 19 7 64 0 286 55
mg_ws_cb(mg_connection*,int,void*) /src/mongoose/src/ws.c 3 ['N/A', 'int', 'N/A'] 12 0 429 67 20 99 0 467 45

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

Functions statically reachable by fuzzers
69.0%
357 / 516
Cyclomatic complexity statically reachable by fuzzers
81.0%
2890 / 3584

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.

test/fuzz.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=['LLVMFuzzerTestOneInput', 'fn(mg_connection*, int, void*)']

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
mg_http_serve_file 78 28 35.89% ['fuzz']
mg_l2_pppoe_rx(mg_tcpip_if*,mg_l2proto*,mg_str*,mg_str*) 62 27 43.54% ['fuzz']
mg_str_to_num 68 37 54.41% ['fuzz']
mg_http_status_code_str(int) 68 7 10.29% ['fuzz']
mg_tcpip_poll(mg_tcpip_if*,unsignedlong) 87 44 50.57% ['fuzz']
rx_arp(mg_tcpip_if*,pkt*) 36 5 13.88% ['fuzz']
rx_ip(mg_tcpip_if*,pkt*) 65 27 41.53% ['fuzz']

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/mongoose/src/jwt.c [] []
/src/mongoose/src/ota_dummy.c [] []
/src/mongoose/src/fmt.c ['fuzz'] ['fuzz']
/src/mongoose/src/http.c ['fuzz'] ['fuzz']
/src/mongoose/src/net_builtin.c ['fuzz'] ['fuzz']
/src/mongoose/src/net.c ['fuzz'] ['fuzz']
/src/mongoose/test/driver_mock.c [] []
/src/mongoose/src/sntp.c ['fuzz'] ['fuzz']
/src/mongoose/src/drivers/phy.c [] []
/src/mongoose/test/mongoose.h [] []
/src/mongoose/src/printf.c ['fuzz'] ['fuzz']
/src/mongoose/src/ws.c [] []
/src/mongoose/src/l2_ppp.c [] []
/src/mongoose/src/sha1.c [] []
/src/mongoose/src/md5.c [] []
/src/mongoose/src/mdash.c ['fuzz'] ['fuzz']
/src/mongoose/src/fs_packed.c [] []
/src/mongoose/src/ota.c ['fuzz'] ['fuzz']
/src/mongoose/src/event.c ['fuzz'] ['fuzz']
/src/mongoose/src/fs_posix.c [] []
/src/mongoose/src/url.c ['fuzz'] ['fuzz']
/src/mongoose/src/json.c ['fuzz'] ['fuzz']
/src/mongoose/src/wifi_dummy.c [] []
/src/mongoose/src/health.c [] []
/src/mongoose/src/l2_eth.c [] []
/src/mongoose/src/fs.c ['fuzz'] ['fuzz']
/src/mongoose/src/ssi.c ['fuzz'] []
/src/mongoose/src/tls_dummy.c ['fuzz'] ['fuzz']
/src/mongoose/src/l2.c ['fuzz'] ['fuzz']
/src/mongoose/test/fuzz.c ['fuzz'] ['fuzz']
/src/mongoose/src/sha256.c [] []
/src/mongoose/src/modbus.c [] []
/src/mongoose/src/iobuf.c ['fuzz'] ['fuzz']
/src/mongoose/src/timer.c ['fuzz'] ['fuzz']
/src/mongoose/src/log.c ['fuzz'] ['fuzz']
/src/mongoose/src/str.c ['fuzz'] ['fuzz']
/src/mongoose/src/queue.c ['fuzz'] []
/src/mongoose/src/mqtt.c ['fuzz'] ['fuzz']
/src/mongoose/src/dns.c ['fuzz'] ['fuzz']
/src/mongoose/src/dash.c [] []
/src/mongoose/src/base64.c ['fuzz'] ['fuzz']
/src/mongoose/src/util.c ['fuzz'] ['fuzz']
/src/mongoose/src/rpc.c [] []

Directories in report

Directory
/src/mongoose/src/
/src/mongoose/test/
/src/mongoose/src/drivers/

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
fuzz fuzzerLogFile-0-JhvYQ92CoI.data fuzzerLogFile-0-JhvYQ92CoI.data.yaml fuzz.covreport