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

Table of contents

Project overview: jupyter_server
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: fuzz_serialization
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
/src/fuzz_serialization.py
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: 2025-07-04

Project overview: jupyter_server

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
1.0%
17 / 1440
Cyclomatic complexity statically reachable by fuzzers
1.0%
60 / 4838
Runtime code coverage of functions
10.0%
147 / 1440

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
fuzz_serialization /src/fuzz_serialization.py 71 2822 6 5 28 219 fuzz_serialization.py

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_serialization

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 67 45.5%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 80 54.4%
All colors 147 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
33 26 jupyter_client.session.json_packer call site: 00026 jupyter_client.jsonutil.json_clean
10 9 jupyter_client.session.Session._check_packers call site: 00009 jupyter_client.jsonutil.squash_dates
6 106 jupyter_client.session.Session.msg call site: 00106 fdp.ConsumeBytes
5 20 jupyter_client.session.Session._check_packers call site: 00020 jupyter_client.session.Session._check_packers.
5 71 jupyter_client.session.Session._check_packers call site: 00071 jupyter_client.session.Session._check_packers.
3 142 jupyter_client.jsonutil.parse_date call site: 00142 warnings.warn
2 97 jupyter_client.session.Session._new_auth call site: 00097 traitlets.log.get_logger
2 103 jupyter_client.session.Session.msg call site: 00103 .isinstance
1 136 jupyter_client.jsonutil.extract_dates call site: 00136 jupyter_client.jsonutil.extract_dates

Runtime coverage analysis

Covered functions
246
Functions that are reachable but not covered
54
Reachable functions
71
Percentage of reachable functions covered
23.94%
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
/ 1
...fuzz_serialization 9
jupyter_client.session 29
jupyter_client.jsonutil 30
jupyter_server.services.kernels.connection.base 13

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
jupyter_server.serverapp.ServerApp.initialize jupyter_server.serverapp 5 ['N/A', 'N/A', 'N/A', 'N/A', 'N/A'] 7 0 20 5 5 158 0 512 482
jupyter_server.auth.decorator.authorized.wrapper.inner jupyter_server.auth.decorator 3 ['N/A', 'N/A', 'N/A'] 5 0 1 6 5 146 0 471 413
jupyter_server.services.contents.filemanager.FileContentsManager.save jupyter_server.services.contents.filemanager 3 ['N/A', 'N/A', 'N/A'] 9 0 12 9 7 98 0 318 261
jupyter_client.manager.in_pending_state.wrapper jupyter_client.manager 3 ['N/A', 'N/A', 'N/A'] 5 0 5 2 4 66 0 215 176
jupyter_client.localinterfaces._load_ips jupyter_client.localinterfaces 1 ['N/A'] 3 0 3 2 4 43 2 140 125
jupyter_server.auth.identity.IdentityProvider._get_user jupyter_server.auth.identity 2 ['N/A', 'N/A'] 4 0 5 8 6 42 1 136 100
jupyter_server.services.kernels.kernelmanager.MappingKernelManager._async_start_kernel jupyter_server.services.kernels.kernelmanager 4 ['N/A', 'N/A', 'N/A', 'N/A'] 6 0 8 6 5 89 0 284 98

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

Functions statically reachable by fuzzers
16.0%
230 / 1440
Cyclomatic complexity statically reachable by fuzzers
17.0%
821 / 4838

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.

/src/fuzz_serialization.py

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=['jupyter_client.session.json_packer', 'jupyter_client.session.Session._check_packers', 'jupyter_client.session.Session.msg', 'jupyter_client.jsonutil.parse_date', 'jupyter_client.session.Session._new_auth', 'jupyter_client.jsonutil.extract_dates']

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
jupyter_client.session.Session.send 41 0 0.0% []
jupyter_client.session.Session.deserialize 41 0 0.0% []
jupyter_client.multikernelmanager.MultiKernelManager.list_kernel_ids 33 0 0.0% []
traitlets.HasTraits.settings.update 1736 362 20.85% ['fuzz_serialization']
q.append 44 22 50.0% ['fuzz_serialization']
traitlets.config.configurable.LoggingConfigurable.__init__ 258 87 33.72% ['fuzz_serialization']
pathlib.Path.relative_to 502 42 8.366% ['fuzz_serialization']
loop.call_later 287 103 35.88% ['fuzz_serialization']
jupyter_core.utils.ensure_dir_exists 106 45 42.45% ['fuzz_serialization']
io.BytesIO 94 46 48.93% ['fuzz_serialization']
jupyter_client.client.KernelClient._async_wait_for_ready 32 0 0.0% []
jupyter_client.client.KernelClient._async_execute_interactive 54 0 0.0% []
time.perf_counter 496 178 35.88% ['fuzz_serialization']
stream.on_recv_stream 732 115 15.71% ['fuzz_serialization']
jupyter_client.connect.write_connection_file 55 0 0.0% []
paths.items 460 62 13.47% ['fuzz_serialization']
re.match 159 72 45.28% ['fuzz_serialization']
platform.platform 99 11 11.11% ['fuzz_serialization']
tornado.httpserver.HTTPServer 128 44 34.37% ['fuzz_serialization']
tornado.concurrent.Future 84 39 46.42% ['fuzz_serialization']
ns.get 75 30 40.0% ['fuzz_serialization']
jupyter_client.launcher.launch_kernel 54 1 1.851% ['fuzz_serialization']
jupyter_client.jsonutil.json_clean 31 0 0.0% ['fuzz_serialization']
tornado.netutil.bind_sockets 234 65 27.77% ['fuzz_serialization']
tornado.httpclient.AsyncHTTPClient.fetch 245 70 28.57% ['fuzz_serialization']
jupyter_server.base.handlers.JupyterHandler.prepare 31 0 0.0% []
tornado.web.RequestHandler.application.last_activity 1476 337 22.83% ['fuzz_serialization']
inspect.isclass 676 118 17.45% ['fuzz_serialization']
template.render 497 108 21.73% ['fuzz_serialization']
tornado.log.app_log.exception 116 27 23.27% ['fuzz_serialization']
resources.get 1640 2 0.121% ['fuzz_serialization']
traitlets.config.application.Application.launch_instance 520 144 27.69% ['fuzz_serialization']
tornado.httputil.format_timestamp 470 141 30.0% ['fuzz_serialization']
tornado.escape.json_encode 127 44 34.64% ['fuzz_serialization']
traitlets.config.loader.JSONFileConfigLoader.load_config 587 153 26.06% ['fuzz_serialization']
tornado.gen.with_timeout 323 77 23.83% ['fuzz_serialization']
tornado.websocket.WebSocketHandler.ping 746 166 22.25% ['fuzz_serialization']
future.add_done_callback 404 73 18.06% ['fuzz_serialization']
zmq.eventloop.zmqstream.ZMQStream 278 74 26.61% ['fuzz_serialization']
connection.disconnect 453 66 14.56% ['fuzz_serialization']
registry.get 111 58 52.25% ['fuzz_serialization']
parser.parse_args 817 128 15.66% ['fuzz_serialization']

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
[] []
concurrent [] []
socketserver [] []
datetime [] []
io [] []
jupyter_server.services.contents.handlers [] []
jupyter_server.gateway.managers [] []
jupyter_client.ssh [] []
jupyter_server.auth.identity [] []
jupyter_server.services.kernels.connection.channels [] []
jupyter_client.channelsabc [] []
_winapi [] []
dateutil [] []
signal [] []
jupyter_server.serverapp [] []
ctypes [] []
netifaces [] []
jupyter_server.view.handlers [] []
jupyter_server.files [] []
json [] []
packaging [] []
pexpect [] []
jupyter_server.services.sessions.sessionmanager [] []
jupyter_server.base.zmqhandlers [] []
jupyter_client.client [] []
jupyter_server.services.config [] []
jupyter_server.services.shutdown [] []
jupyter_server.base.websocket [] []
jupyter_server._version [] []
jupyter_server.base.handlers [] []
jupyter_server.auth.decorator [] []
hashlib [] []
jupyter_server.services.security.handlers [] []
queue [] []
jupyter_client.kernelspec [] []
jupyter_client.manager [] []
jupyter_server.services.contents.fileio [] []
jupyter_server.extension.serverextension [] []
colorama [] []
...fuzz_serialization ['fuzz_serialization'] []
jupyter_server.services.events.handlers [] []
jupyter_server.services.config.handlers [] []
sys [] []
argon2 [] []
jupyter_client.adapter [] []
jupyter_client.clientabc [] []
ipykernel [] []
threading [] []
jupyter_server.auth.authorizer [] []
jupyter_server._tz [] []
[] []
jupyter_server.services.contents.manager [] []
jupyter_client.blocking [] []
jupyter_events [] []
itertools [] []
jupyter_server.services.kernelspecs [] []
jupyter_server.services.kernels.websocket [] []
weakref [] []
fnmatch [] []
jupyter_client.threaded [] []
jupyter_client.win_interrupt [] []
argparse [] []
gettext [] []
jupyter_server.extension [] []
jupyter_server.extension.handler [] []
jupyter_server.base [] []
jupyter_server.gateway [] []
platform [] []
subprocess [] []
jupyter_client.blocking.client [] []
multiprocessing [] []
uuid [] []
jupyter_client.ssh.tunnel [] []
jupyter_client.kernelapp [] []
jupyter_server.auth.login [] []
jupyter_server.services.kernels.connection [] []
jupyter_server.services.api.handlers [] []
jupyter_server.services.security [] []
jupyter_client.provisioning.local_provisioner [] []
importlib_metadata [] []
contextvars [] []
jupyter_server.auth.__main__ [] []
shutil [] []
math [] []
pysqlite2 [] []
find_connection_file [] []
textwrap [] []
jupyter_server.transutils [] []
importlib [] []
jupyter_server.gateway.gateway_client [] []
glob [] []
jupyter_server [] []
types [] []
pathlib [] []
jupyter_server.extension.application [] []
jupyter_client.localinterfaces [] []
jupyter_client.managerabc [] []
jupyter_server.services.kernelspecs.handlers [] []
jupyter_server.__main__ [] []
jupyter_client.asynchronous [] []
logging [] []
jupyter_client.utils [] []
time [] []
jupyter_client.ioloop [] []
jupyter_server.services.contents.filemanager [] []
struct [] []
jupyter_client.jsonutil ['fuzz_serialization'] []
IPython [] []
jupyter_server.services.events [] []
jupyter_client.runapp [] []
jupyter_server.nbconvert [] []
stat [] []
jupyter_client.channels [] []
jupyter_client.multikernelmanager [] []
zipfile [] []
jupyter_client.launcher [] []
random [] []
jinja2 [] []
os [] []
traceback [] []
collections [] []
jupyter_server.auth.utils [] []
jupyter_client.ssh.forward [] []
zmq [] []
jupyter_server.traittypes [] []
sqlite3 [] []
jupyter_server.pytest_plugin [] []
nbformat [] []
jupyter_server.services.config.manager [] []
jupyter_client._version [] []
jupyter_server.services.contents [] []
jupyter_client.connect [] []
jupyter_server.extension.config [] []
ast [] []
jupyter_server.extension.utils [] []
jupyter_server._sysinfo [] []
jupyter_server.utils [] []
jupyter_server.services.sessions [] []
binascii [] []
re [] []
jupyter_client.provisioning.factory [] []
jupyter_server.services.contents.checkpoints [] []
jupyter_server.services.kernels.connection.base ['fuzz_serialization'] []
jupyter_client.provisioning [] []
jupyter_server.services.kernels.kernelmanager [] []
jupyter_server.services [] []
nbconvert [] []
jupyter_server.services.nbconvert.handlers [] []
select [] []
abc [] []
socket [] []
dataclasses [] []
getpass [] []
ipaddress [] []
email [] []
jupyter_server.kernelspecs [] []
jupyter_server.services.api [] []
jupyter_server.gateway.handlers [] []
jupyter_client.ioloop.restarter [] []
jupyter_server.extension.manager [] []
jupyter_server.terminal [] []
jupyter_server.terminal.api_handlers [] []
hmac [] []
jupyter_server.config_manager [] []
jupyter_server.auth [] []
atexit [] []
jupyter_client.ioloop.manager [] []
jupyter_server.prometheus [] []
copy [] []
pickle [] []
http [] []
jupyter_client [] []
jupyter_server.nbconvert.handlers [] []
tornado [] []
jupyter_server.terminal.terminalmanager [] []
jupyter_server.services.kernels [] []
jupyter_core [] []
jupyter_server.services.kernels.handlers [] []
urllib [] []
jupyter_server.auth.logout [] []
jupyter_server.services.contents.filecheckpoints [] []
jupyter_server.base.call_context [] []
jupyter_server.services.kernels.connection.abc [] []
tempfile [] []
jupyter_server.i18n [] []
jupyter_client.consoleapp [] []
jupyter_client.provisioning.provisioner_base [] []
jupyter_server.gateway.connections [] []
jupyter_client.session ['fuzz_serialization'] []
send2trash [] []
pprint [] []
jupyter_server.prometheus.log_functions [] []
jupyter_server.services.contents.largefilemanager [] []
anyio [] []
jupyter_server.view [] []
tunnel_to_kernel [] []
webbrowser [] []
atheris [] []
inspect [] []
mimetypes [] []
asyncio [] []
jupyter_server.kernelspecs.handlers [] []
jupyter_server.prometheus.metrics [] []
jupyter_server.terminal.handlers [] []
functools [] []
typing [] []
jupyter_server.services.sessions.handlers [] []
warnings [] []
jupyter_client.asynchronous.client [] []
_subprocess [] []
jupyter_server.files.handlers [] []
base64 [] []
jupyter_client.kernelspecapp [] []
psutil [] []
jupyter_server.log [] []
jupyter_client.restarter [] []
notebook [] []
jupyter_server.services.nbconvert [] []
websocket [] []
resource [] []
paramiko [] []
prometheus_client [] []
traitlets [] []
jupyter_server.auth.security [] []

Directories in report

Directory

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_serialization fuzzerLogFile-fuzz_serialization.data fuzzerLogFile-fuzz_serialization.data.yaml all_cov.json