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

Table of contents

Project overview: jupyter-nbconvert
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: fuzz_markdown_converter
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_markdown_converter.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: 2025-07-11

Project overview: jupyter-nbconvert

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
1.0%
4 / 304
Cyclomatic complexity statically reachable by fuzzers
1.0%
14 / 1028
Runtime code coverage of functions
21.0%
63 / 304

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_markdown_converter /src/fuzz_markdown_converter.py 12 854 3 3 5 35 fuzz_markdown_converter.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_markdown_converter

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 2 13.3%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 13 86.6%
All colors 15 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
1 7 nbconvert.filters.markdown_mistune.MarkdownWithMath.__init__ call site: 00007 mistune.InlineParser.__init__
1 13 nbconvert.filters.markdown_mistune.MarkdownWithMath.render call site: 00013 fdp.ConsumeUnicodeNoSurrogates

Runtime coverage analysis

Covered functions
177
Functions that are reachable but not covered
7
Reachable functions
12
Percentage of reachable functions covered
41.67%
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_markdown_converter 3
nbconvert.filters.markdown_mistune 8

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
nbconvert.nbconvertapp.NbConvertApp.convert_notebooks nbconvert.nbconvertapp 1 ['N/A'] 6 0 6 5 5 41 1 132 132
nbconvert.exporters.pdf.PDFExporter.from_notebook_node nbconvert.exporters.pdf 4 ['N/A', 'N/A', 'N/A', 'N/A'] 4 0 7 3 4 33 0 102 90
nbconvert.writers.files.FilesWriter.write nbconvert.writers.files 5 ['N/A', 'N/A', 'N/A', 'N/A', 'N/A'] 4 0 11 7 6 28 0 93 72
nbconvert.filters.ansi._ansi2anything nbconvert.filters.ansi 2 ['N/A', 'N/A'] 2 0 6 19 11 17 2 74 65
nbconvert.exporters.templateexporter.TemplateExporter._init_preprocessors nbconvert.exporters.templateexporter 1 ['N/A'] 3 0 3 2 4 23 0 77 65
nbconvert.nbconvertapp.NbConvertApp.initialize nbconvert.nbconvertapp 2 ['N/A', 'N/A'] 3 0 8 2 4 30 0 97 64
nbconvert.filters.markdown.markdown2asciidoc nbconvert.filters.markdown 2 ['N/A', 'N/A'] 4 0 1 2 4 21 0 69 60
nbconvert.exporters.exporter.Exporter.from_filename nbconvert.exporters.exporter 4 ['N/A', 'N/A', 'N/A', 'N/A'] 5 0 1 3 4 22 0 74 59
nbconvert.preprocessors.extractoutput.ExtractOutputPreprocessor.preprocess_cell nbconvert.preprocessors.extractoutput 4 ['N/A', 'N/A', 'N/A', 'N/A'] 2 0 2 12 8 18 0 63 54
nbconvert.exporters.webpdf.WebPDFExporter.run_playwright.main nbconvert.exporters.webpdf 1 ['N/A'] 1 0 10 2 4 13 2 43 43

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

Functions statically reachable by fuzzers
19.0%
57 / 304
Cyclomatic complexity statically reachable by fuzzers
23.0%
232 / 1028

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_markdown_converter.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=['nbconvert.filters.markdown_mistune.MarkdownWithMath.__init__', 'nbconvert.filters.markdown_mistune.MarkdownWithMath.render']

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
tornado.gen.coroutine 323 82 25.38% ['fuzz_markdown_converter']
tornado.web.Application 1476 334 22.62% ['fuzz_markdown_converter']
traitlets.config.catch_config_error 1736 220 12.67% ['fuzz_markdown_converter']
traitlets.config.configurable.LoggingConfigurable.postprocessor_factory 258 62 24.03% ['fuzz_markdown_converter']
tornado.httpclient.AsyncHTTPClient 245 70 28.57% ['fuzz_markdown_converter']
tornado.httpserver.HTTPServer 128 44 34.37% ['fuzz_markdown_converter']
loop.run_until_complete 287 103 35.88% ['fuzz_markdown_converter']
nbconvert.filters.ansi._latexconverter 35 0 0.0% []
nbconvert.filters.ansi._ansi2anything 65 0 0.0% []
markupsafe.Markup 182 73 40.10% ['fuzz_markdown_converter']
stream.write 564 86 15.24% ['fuzz_markdown_converter']
p.communicate 53 9 16.98% ['fuzz_markdown_converter']
pandocfilters.RawInline 152 55 36.18% ['fuzz_markdown_converter']
info.strip 38 16 42.10% ['fuzz_markdown_converter']
pygments.lexers.get_lexer_by_name 192 62 32.29% ['fuzz_markdown_converter']
pygments.formatters.LatexFormatter.get_style_defs 86 38 44.18% ['fuzz_markdown_converter']
bs4.BeautifulSoup.select 417 77 18.46% ['fuzz_markdown_converter']
element.decode 994 313 31.48% ['fuzz_markdown_converter']
xml.etree.ElementTree.Element.append 205 8 3.902% ['fuzz_markdown_converter']
s.capture 108 10 9.259% ['fuzz_markdown_converter']
nbconvert.exporters.pdf.PDFExporter.run_command 31 0 0.0% []
nbconvert.preprocessors.extractoutput.ExtractOutputPreprocessor.preprocess_cell 36 0 0.0% []
resources.pop 1640 2 0.121% ['fuzz_markdown_converter']
nbclient.client.NotebookClient.execute_cell 521 102 19.57% ['fuzz_markdown_converter']
nbformat.writes 60 22 36.66% ['fuzz_markdown_converter']
pygments.lexers.special.TextLexer 80 38 47.5% ['fuzz_markdown_converter']
nbconvert.writers.files.FilesWriter.write 36 0 0.0% []
nbconvert.exporters.templateexporter.TemplateExporter.get_template_names 48 0 0.0% []
template.endswith 497 108 21.73% ['fuzz_markdown_converter']
paths.append 460 93 20.21% ['fuzz_markdown_converter']
nbformat.validator.normalize 273 40 14.65% ['fuzz_markdown_converter']
nbconvert.exporters.slides._RevealMetadataPreprocessor.preprocess 39 3 7.692% ['fuzz_markdown_converter']
nbconvert.exporters.webpdf.WebPDFExporter.run_playwright.main 37 0 0.0% []
concurrent.futures.ThreadPoolExecutor 84 39 46.42% ['fuzz_markdown_converter']
asyncio.set_event_loop_policy 94 46 48.93% ['fuzz_markdown_converter']
nbconvert.exporters.html.find_lab_theme 31 12 38.70% ['fuzz_markdown_converter']
nbconvert.exporters.html.HTMLExporter._init_resources.resources_include_url 35 0 0.0% []
context.get 169 66 39.05% ['fuzz_markdown_converter']
jinja2.loaders.split_template_path 279 71 25.44% ['fuzz_markdown_converter']

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
[] []
markupsafe [] []
nbconvert.utils.exceptions [] []
codecs [] []
nbconvert.exporters.webpdf [] []
nbconvert.utils.version [] []
nbconvert.exporters.script [] []
nbconvert.preprocessors.tagremove [] []
nbconvert.postprocessors [] []
nbconvert.exporters [] []
base64 [] []
nbconvert.preprocessors.highlightmagics [] []
nbconvert.preprocessors.clearmetadata [] []
glob [] []
datetime [] []
nbconvert.filters.citation [] []
nbconvert.filters.latex [] []
random [] []
tornado [] []
warnings [] []
nbconvert.exporters.latex [] []
nbconvert.resources [] []
defusedxml [] []
asyncio [] []
nbconvert.exporters.markdown [] []
xml [] []
pathlib [] []
nbconvert.writers.stdout [] []
nbconvert.utils._contextlib_chdir [] []
mistune [] []
nbconvert.utils.lexers [] []
collections [] []
nbconvert.preprocessors.extractattachments [] []
urllib [] []
jinja2 [] []
nbconvert.utils.base [] []
pandocfilters [] []
io [] []
IPython [] []
nbconvert.preprocessors.csshtmlheader [] []
pygments [] []
binascii [] []
nbconvert.writers.debug [] []
nbconvert.exporters.asciidoc [] []
traitlets [] []
nbconvert.exporters.qtpdf [] []
webbrowser [] []
_winreg [] []
nbconvert.exporters.base [] []
nbconvert.utils.pandoc [] []
nbconvert.preprocessors.sanitize [] []
nbconvert.preprocessors.convertfigures [] []
bleach [] []
html [] []
nbconvert.exporters.qt_screenshot [] []
nbconvert.postprocessors.base [] []
nbconvert.utils.iso639_1 [] []
nbconvert.exporters.html [] []
nbconvert.filters.metadata [] []
[] []
nbconvert.exporters.rst [] []
jupyter_core [] []
nbconvert.filters.pandoc [] []
nbconvert.utils [] []
nbconvert.writers [] []
pprint [] []
nbconvert.exporters.notebook [] []
bs4 [] []
sys [] []
nbconvert.filters.filter_links [] []
nbconvert.exporters.templateexporter [] []
nbconvert.writers.files [] []
nbconvert.exporters.qtpng [] []
nbconvert.filters.datatypefilter [] []
playwright [] []
nbconvert.preprocessors.svg2pdf [] []
nbconvert.exporters.pdf [] []
nbconvert.utils.io [] []
nbconvert.exporters.exporter [] []
os [] []
nbconvert.preprocessors [] []
nbconvert.filters.markdown [] []
json [] []
nbconvert.filters.markdown_mistune ['fuzz_markdown_converter'] []
atheris [] []
nbconvert.__main__ [] []
tempfile [] []
nbconvert.preprocessors.coalescestreams [] []
packaging [] []
subprocess [] []
nbconvert.nbconvertapp [] []
nbconvert.filters.ansi [] []
shutil [] []
nbconvert.conftest [] []
re [] []
nbconvert.filters.strings [] []
winreg [] []
nbconvert.exporters.slides [] []
nbconvert.preprocessors.extractoutput [] []
nbconvert.preprocessors.base [] []
copy [] []
nbconvert.exporters.python [] []
hashlib [] []
nbconvert.preprocessors.execute [] []
typing [] []
textwrap [] []
importlib_metadata [] []
nbconvert.writers.base [] []
nbconvert.preprocessors.clearoutput [] []
nbformat [] []
nbconvert._version [] []
PyQt5 [] []
nbconvert.filters.widgetsdatatypefilter [] []
nbconvert.utils.text [] []
nbconvert.preprocessors.regexremove [] []
mimetypes [] []
nbconvert.filters.highlight [] []
nbclient [] []
nbconvert.filters [] []
nbconvert.exporters.qt_exporter [] []
threading [] []
nbconvert.preprocessors.latex [] []
importlib [] []
nbconvert [] []
nbconvert.postprocessors.serve [] []
...fuzz_markdown_converter ['fuzz_markdown_converter'] []

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_markdown_converter fuzzerLogFile-fuzz_markdown_converter.data fuzzerLogFile-fuzz_markdown_converter.data.yaml all_cov.json