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

Table of contents

Project overview: bleach
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: linkify_fuzzer
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Fuzzer: sanitize_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
/src/linkify_fuzzer.py
Dictionary
Fuzzer function priority
/src/sanitize_fuzzer.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: 2026-01-17

Project overview: bleach

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
22.0%
159 / 739
Cyclomatic complexity statically reachable by fuzzers
26.0%
673 / 2619
Runtime code coverage of functions
31.0%
229 / 739

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
linkify_fuzzer /src/linkify_fuzzer.py 208 1021 12 11 366 769 linkify_fuzzer.py
sanitize_fuzzer /src/sanitize_fuzzer.py 313 919 14 18 601 1176 sanitize_fuzzer.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: linkify_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 0 331 42.1%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 455 57.8%
All colors 786 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
68 55 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00055 bleach._vendor.html5lib._inputstream.HTMLBinaryInputStream.__init__
14 141 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.readChunk call site: 00141 bleach._vendor.html5lib._utils.isSurrogatePair
14 483 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00483 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
13 41 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00041 bleach._vendor.html5lib._inputstream.BufferedStream.seek
10 436 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00436 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
9 600 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00600 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
8 351 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00351 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
8 522 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00522 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
8 695 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00695 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
7 227 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00227 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
7 294 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00294 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
7 467 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00467 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil

Runtime coverage analysis

Covered functions
287
Functions that are reachable but not covered
127
Reachable functions
208
Percentage of reachable functions covered
38.94%
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
...linkify_fuzzer 3
bleach 2
bleach.linkifier 9
bleach.html5lib_shim 32
bleach._vendor.html5lib.serializer 7
bleach._vendor.html5lib.html5parser 22
bleach._vendor.html5lib._tokenizer 88
bleach._vendor.html5lib._inputstream 61
bleach._vendor.html5lib._utils 2
bleach._vendor.html5lib._trie.py 3

Fuzzer: sanitize_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 0 580 51.5%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 545 48.4%
All colors 1125 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
79 991 bleach.sanitizer.BleachSanitizerFilter.sanitize_stream call site: 00991 bleach._vendor.html5lib.filters.inject_meta_charset.Filter.__iter__
78 864 bleach.html5lib_shim.match_entity call site: 00864 bleach._vendor.html5lib.filters.inject_meta_charset.Filter.__iter__
67 58 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00058 bleach._vendor.html5lib._inputstream.HTMLBinaryInputStream.__init__
31 225 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.processEntityInAttribute call site: 00225 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.consumeNumberEntity
19 260 bleach._vendor.html5lib._trie.py.Trie.has_keys_with_prefix call site: 00260 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
15 839 bleach.sanitizer.BleachSanitizerFilter.merge_characters call site: 00839 bleach._vendor.html5lib.filters.alphabeticalattributes.Filter.__iter__
14 154 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.readChunk call site: 00154 bleach._vendor.html5lib._utils.isSurrogatePair
14 678 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00678 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
13 43 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00043 bleach._vendor.html5lib._inputstream.BufferedStream.seek
11 968 bleach.sanitizer.BleachSanitizerFilter.sanitize_uri_value call site: 00968 normalized_uri.split
10 325 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00325 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
9 668 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00668 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char

Runtime coverage analysis

Covered functions
287
Functions that are reachable but not covered
211
Reachable functions
313
Percentage of reachable functions covered
32.59%
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
/ 1
...sanitize_fuzzer 3
bleach 2
bleach.sanitizer 50
bleach.html5lib_shim 33
bleach._vendor.html5lib.serializer 29
bleach._vendor.html5lib.html5parser 22
bleach._vendor.html5lib._tokenizer 95
bleach._vendor.html5lib._inputstream 60
bleach._vendor.html5lib._utils 2
bleach._vendor.html5lib._trie.py 3
bleach._vendor.html5lib._trie._base 2
bleach._vendor.html5lib.filters.optionaltags 5
bleach._vendor.html5lib.filters.alphabeticalattributes 10
bleach.linkifier 29
bleach._vendor.html5lib.filters.inject_meta_charset 13
bleach._vendor.html5lib.filters.whitespace 8
bleach._vendor.html5lib.filters.sanitizer 38

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
bleach._vendor.parse.urljoin bleach._vendor.parse 3 ['N/A', 'N/A', 'N/A'] 5 0 4 12 8 36 0 126 114
bleach._vendor.html5lib.treewalkers.base.NonRecursiveTreeWalker.__iter__ bleach._vendor.html5lib.treewalkers.base 1 ['N/A'] 2 0 8 13 8 16 0 57 54
bleach._vendor.parse.urlencode bleach._vendor.parse 6 ['N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A'] 5 0 6 9 7 19 0 69 54
bleach._vendor.html5lib.html5parser.getPhases.InBodyPhase.startTagA bleach._vendor.html5lib.html5parser 2 ['N/A', 'N/A'] 2 0 6 3 4 16 0 59 53
bleach._vendor.html5lib.treebuilders.etree_lxml.TreeBuilder.insertRoot bleach._vendor.html5lib.treebuilders.etree_lxml 2 ['N/A', 'N/A'] 2 0 5 7 6 16 0 54 48
bleach._vendor.html5lib.treebuilders.etree_lxml.testSerializer.serializeElement bleach._vendor.html5lib.treebuilders.etree_lxml 2 ['N/A', 'N/A'] 2 0 15 12 8 15 2 58 46
bleach._vendor.html5lib._inputstream.EncodingParser.handleMeta bleach._vendor.html5lib._inputstream 1 ['N/A'] 3 0 0 10 7 18 0 70 45
bleach._vendor.html5lib._utils.moduleFactoryFactory.moduleFactory bleach._vendor.html5lib._utils 3 ['N/A', 'N/A', 'N/A'] 2 0 1 4 5 14 0 47 38
bleach._vendor.parse.parse_qsl bleach._vendor.parse 7 ['N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A'] 3 0 3 8 6 18 1 64 36

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

Functions statically reachable by fuzzers
28.9%
214 / 739
Cyclomatic complexity statically reachable by fuzzers
34.0%
903 / 2619

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/linkify_fuzzer.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=['bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__', 'bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.readChunk', 'bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__']

/src/sanitize_fuzzer.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=['bleach.sanitizer.BleachSanitizerFilter.sanitize_stream', 'bleach.html5lib_shim.match_entity', 'bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__', 'bleach._vendor.html5lib._tokenizer.HTMLTokenizer.processEntityInAttribute', 'bleach._vendor.html5lib._trie.py.Trie.has_keys_with_prefix', 'bleach.sanitizer.BleachSanitizerFilter.merge_characters', 'bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.readChunk', 'bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__', 'bleach.sanitizer.BleachSanitizerFilter.sanitize_uri_value']

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
bleach.linkifier.LinkifyFilter.handle_links 41 0 0.0% ['sanitize_fuzzer']
bleach.linkifier.LinkifyFilter.__iter__ 31 0 0.0% ['sanitize_fuzzer']
bleach._vendor.html5lib._inputstream.HTMLBinaryInputStream.determineEncoding 41 0 0.0% ['linkify_fuzzer', 'sanitize_fuzzer']
bleach._vendor.html5lib._inputstream.EncodingParser.getAttribute 52 0 0.0% []
bleach._vendor.html5lib.filters.sanitizer.Filter.allowed_token 33 0 0.0%
bleach._vendor.html5lib._tokenizer.HTMLTokenizer.consumeEntity 43 0 0.0% ['sanitize_fuzzer']
webencodings.lookup 123 45 36.58% ['linkify_fuzzer', 'sanitize_fuzzer']
bleach._vendor.html5lib.treebuilders.etree.getETreeBuilder.testSerializer.serializeElement 47 0 0.0% []
bleach._vendor.html5lib.treebuilders.etree.getETreeBuilder.tostring.serializeElement 39 7 17.94% ['linkify_fuzzer', 'sanitize_fuzzer']
bleach._vendor.parse.urljoin 39 0 0.0% []
bleach._vendor.parse.urlencode 39 0 0.0% []

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
bleach.html5lib_shim ['linkify_fuzzer', 'sanitize_fuzzer'] []
[] []
webencodings [] []
weakref [] []
bleach._vendor.html5lib.treewalkers.genshi [] []
itertools [] []
bleach._vendor.html5lib.treewalkers.base [] []
bleach.sanitizer ['sanitize_fuzzer'] []
bleach.parse_shim [] []
bleach._vendor.html5lib.filters.lint [] []
...linkify_fuzzer ['linkify_fuzzer'] []
bleach.six_shim [] []
bisect [] []
bleach._vendor.html5lib.treebuilders.etree_lxml [] []
bleach._vendor.html5lib.filters.alphabeticalattributes ['sanitize_fuzzer'] []
atheris [] []
bleach._vendor.html5lib.treebuilders.base [] []
bleach._vendor.html5lib._utils ['linkify_fuzzer', 'sanitize_fuzzer'] []
bleach._vendor.html5lib.treebuilders.dom [] []
bleach ['linkify_fuzzer', 'sanitize_fuzzer'] []
bleach._vendor [] []
copy [] []
bleach._vendor.html5lib.treebuilders [] []
bleach.linkifier ['linkify_fuzzer', 'sanitize_fuzzer'] []
...sanitize_fuzzer ['sanitize_fuzzer'] []
bleach._vendor.html5lib [] []
unicodedata [] []
bleach._vendor.html5lib.filters.inject_meta_charset ['sanitize_fuzzer'] []
bleach._vendor.html5lib.treeadapters.genshi [] []
[] []
io [] []
sys [] []
genshi [] []
lxml [] []
tinycss2 [] []
bleach.css_sanitizer [] []
bleach._vendor.parse [] []
bleach._vendor.html5lib.constants [] []
re [] []
bleach._vendor.html5lib.serializer ['linkify_fuzzer', 'sanitize_fuzzer'] []
bleach._vendor.html5lib.filters.whitespace ['sanitize_fuzzer'] []
bleach._vendor.html5lib.filters [] []
warnings [] []
bleach._vendor.html5lib.treewalkers.etree [] []
collections [] []
bleach._vendor.html5lib.treewalkers.dom [] []
bleach._vendor.html5lib._inputstream ['linkify_fuzzer', 'sanitize_fuzzer'] []
bleach.callbacks [] []
bleach._vendor.html5lib.treebuilders.etree [] []
operator [] []
bleach._vendor.html5lib.treewalkers.etree_lxml [] []
bleach._vendor.html5lib._tokenizer ['linkify_fuzzer', 'sanitize_fuzzer'] []
urllib [] []
codecs [] []
bleach._vendor.html5lib.treewalkers [] []
bleach._vendor.html5lib._trie [] []
bleach._vendor.html5lib.filters.base [] []
bleach._vendor.html5lib.html5parser ['linkify_fuzzer', 'sanitize_fuzzer'] []
bleach._vendor.html5lib.treeadapters [] []
bleach._vendor.html5lib.filters.optionaltags ['sanitize_fuzzer'] []
bleach._vendor.html5lib._trie._base ['sanitize_fuzzer'] []
bleach._vendor.html5lib.treeadapters.sax [] []
types [] []
bleach._vendor.html5lib._ihatexml [] []
bleach._vendor.html5lib.filters.sanitizer ['sanitize_fuzzer'] []
xml [] []
chardet [] []
bleach._vendor.html5lib._trie.py ['linkify_fuzzer', 'sanitize_fuzzer'] []

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
linkify_fuzzer fuzzerLogFile-linkify_fuzzer.data fuzzerLogFile-linkify_fuzzer.data.yaml all_cov.json
sanitize_fuzzer fuzzerLogFile-sanitize_fuzzer.data fuzzerLogFile-sanitize_fuzzer.data.yaml all_cov.json