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: sanitize_fuzzer
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Fuzzer: linkify_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/sanitize_fuzzer.py
Dictionary
Fuzzer function priority
/src/linkify_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: 2025-12-05

Project overview: bleach

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
21.0%
158 / 736
Cyclomatic complexity statically reachable by fuzzers
26.0%
668 / 2610
Runtime code coverage of functions
31.0%
227 / 736

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
sanitize_fuzzer /src/sanitize_fuzzer.py 294 937 16 18 575 1108 sanitize_fuzzer.py
linkify_fuzzer /src/linkify_fuzzer.py 206 1023 12 11 365 763 linkify_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: 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 0 545 50.4%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 535 49.5%
All colors 1080 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
66 60 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00060 bleach._vendor.html5lib._inputstream.HTMLBinaryInputStream.__init__
59 966 bleach.sanitizer.BleachSanitizerFilter.sanitize_stream call site: 00966 bleach._vendor.html5lib.filters.inject_meta_charset.Filter.__iter__
51 846 bleach.html5lib_shim.match_entity call site: 00846 bleach._vendor.html5lib.filters.optionaltags.Filter.__iter__
31 217 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.processEntityInAttribute call site: 00217 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.consumeNumberEntity
19 252 bleach._vendor.html5lib._trie.py.Trie.has_keys_with_prefix call site: 00252 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
17 900 bleach.sanitizer.BleachSanitizerFilter.merge_characters call site: 00900 bleach._vendor.html5lib.filters.optionaltags.Filter.__iter__
14 159 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.readChunk call site: 00159 bleach._vendor.html5lib._utils.isSurrogatePair
14 822 bleach.sanitizer.Cleaner.clean call site: 00822 bleach._vendor.html5lib.serializer.HTMLSerializer.serialize
13 46 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00046 bleach._vendor.html5lib._inputstream.BufferedStream.seek
11 943 bleach.sanitizer.BleachSanitizerFilter.sanitize_uri_value call site: 00943 normalized_uri.split
10 472 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00472 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
9 760 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00760 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char

Runtime coverage analysis

Covered functions
287
Functions that are reachable but not covered
195
Reachable functions
294
Percentage of reachable functions covered
33.67%
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.
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 94
bleach._vendor.html5lib._inputstream 61
bleach._vendor.html5lib._utils 2
bleach._vendor.html5lib._trie.py 3
bleach._vendor.html5lib._trie._base 2
bleach._vendor.html5lib.filters.whitespace 8
bleach.linkifier 29
bleach._vendor.html5lib.filters.optionaltags 5
bleach._vendor.html5lib.filters.inject_meta_charset 13
bleach._vendor.html5lib.filters.alphabeticalattributes 10
bleach._vendor.html5lib.filters.sanitizer 9

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 0 332 42.3%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 452 57.6%
All colors 784 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
66 52 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00052 bleach._vendor.html5lib._inputstream.HTMLBinaryInputStream.__init__
14 140 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.readChunk call site: 00140 bleach._vendor.html5lib._utils.isSurrogatePair
14 358 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00358 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
13 38 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__ call site: 00038 bleach._vendor.html5lib._inputstream.BufferedStream.seek
10 238 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00238 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
9 380 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00380 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
8 415 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00415 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
8 510 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00510 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
8 662 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00662 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil
7 200 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00200 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
7 258 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00258 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.char
7 424 bleach._vendor.html5lib._tokenizer.HTMLTokenizer.__iter__ call site: 00424 bleach._vendor.html5lib._inputstream.HTMLUnicodeInputStream.charsUntil

Runtime coverage analysis

Covered functions
287
Functions that are reachable but not covered
126
Reachable functions
206
Percentage of reachable functions covered
38.83%
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 59
bleach._vendor.html5lib._utils 2
bleach._vendor.html5lib._trie.py 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
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.html5lib.treebuilders.etree_lxml.TreeBuilder.insertRoot bleach._vendor.html5lib.treebuilders.etree_lxml 2 ['N/A', 'N/A'] 2 0 5 7 6 18 0 60 54
bleach._vendor.parse.urlencode bleach._vendor.parse 6 ['N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A'] 4 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.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
28.0%
209 / 736
Cyclomatic complexity statically reachable by fuzzers
34.0%
886 / 2610

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/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._vendor.html5lib._inputstream.HTMLUnicodeInputStream.__init__', 'bleach.sanitizer.BleachSanitizerFilter.sanitize_stream', 'bleach.html5lib_shim.match_entity', '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.sanitizer.Cleaner.clean', 'bleach.sanitizer.BleachSanitizerFilter.sanitize_uri_value']

/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__']

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

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