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

Table of contents

Project overview: libvnc
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: fuzz_server
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/libvncserver/test/fuzz_server.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: 2025-10-10

Project overview: libvnc

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
22.0%
107 / 482
Cyclomatic complexity statically reachable by fuzzers
22.0%
923 / 4186
Runtime code coverage of functions
20.0%
95 / 482

Fuzzers overview

Fuzzer Fuzzer filename Functions Reached Functions unreached Fuzzer depth Files reached Basic blocks reached Cyclomatic complexity Details
fuzz_server /src/libvncserver/test/fuzz_server.c 181 471 8 20 2528 1073 fuzz_server.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_server

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 0 489 59.5%
gold [1:9] 56 6.82%
yellow [10:29] 13 1.58%
greenyellow [30:49] 12 1.46%
lawngreen 50+ 251 30.5%
All colors 821 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
119 563 rfbProcessFileTransfer call site: 00563 rfbSendDirContent
59 36 rfbReleaseExtensionIterator call site: 00036 rfbUsage
40 711 rfbProcessClientNormalMessage call site: 00711 rfbSendExtendedServerCutTextData
30 292 encodingName call site: 00292 snprintf
27 5 rfbGetScreen call site: 00005 rfbUsage
16 514 rfbProcessClientNormalMessage call site: 00514 rfbSetClientColourMap
13 366 rfbSendSecurityType call site: 00366 rfbVncAuthSendChallenge
11 102 rfbInitServerWithPthreadsAndZRLE call site: 00102 rfbListenOnTCPPort
10 230 rfbClientConnectionGone call site: 00230 rfbFreeTightData
10 401 rfbProcessClientSecurityType call site: 00401 rfbAuthProcessClientMessage
9 533 sraRgnSubtract call site: 00533 sraSpanListSubtract
8 418 rfbProcessClientInitMessage call site: 00418 rfbCloseClient

Runtime coverage analysis

Covered functions
96
Functions that are reachable but not covered
104
Reachable functions
181
Percentage of reachable functions covered
42.54%
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
/src/libvncserver/test/fuzz_server.c 1
libvncserver/main.c 8
libvncserver/cargs.c 3
libvncserver/sockets.c 10
libvncserver/rfbserver.c 28
common/sockets.c 1
libvncserver/httpd.c 1
libvncserver/stats.c 8
libvncserver/rfbregion.c 21
libvncserver/rfbssl_openssl.c 1
libvncserver/zrle.c 1
libvncserver/zrleoutstream.c 2
libvncserver/tight.c 1
common/turbojpeg.c 1
libvncserver/ultra.c 1
libvncserver/auth.c 8
common/vncauth.c 1
libvncserver/cursor.c 1
libvncserver/scale.c 9
libvncserver/translate.c 1

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
rfbRunEventLoop /src/libvncserver/src/libvncserver/main.c 3 ['N/A', 'size_t', 'char'] 14 0 96 15 6 370 0 3121 2221
webSocketsCheck /src/libvncserver/src/libvncserver/websockets.c 1 ['N/A'] 4 0 162 27 11 38 0 153 127
webSocketsDecode /src/libvncserver/src/libvncserver/websockets.c 3 ['N/A', 'N/A', 'int'] 4 0 31 3 2 18 0 109 97
tjDecompress /src/libvncserver/src/common/turbojpeg.c 9 ['N/A', 'N/A', 'size_t', 'N/A', 'int', 'int', 'int', 'int', 'int'] 3 0 41 3 2 11 0 76 62
rfbDefaultPasswordCheck /src/libvncserver/src/libvncserver/main.c 3 ['N/A', 'N/A', 'int'] 3 0 101 12 5 18 0 59 51
rfbSetTranslateFunction /src/libvncserver/src/libvncserver/translate.c 1 ['N/A'] 4 0 654 74 31 15 0 83 46
rfbUltraVNCRepeaterMode2Connection /src/libvncserver/src/libvncserver/rfbserver.c 4 ['N/A', 'N/A', 'int', 'N/A'] 13 0 140 18 8 345 0 2897 39

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

Functions statically reachable by fuzzers
68.0%
329 / 482
Cyclomatic complexity statically reachable by fuzzers
82.0%
3432 / 4186

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/libvncserver/test/fuzz_server.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=['rfbProcessFileTransfer', 'rfbReleaseExtensionIterator', 'rfbProcessClientNormalMessage', 'encodingName', 'rfbGetScreen', 'rfbSendSecurityType', 'rfbInitServerWithPthreadsAndZRLE', 'rfbClientConnectionGone', 'rfbProcessClientSecurityType']

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
rfbProcessArguments 154 6 3.896% ['fuzz_server']
sraSpanListSubtract 54 8 14.81% ['fuzz_server']
rfbProcessFileTransfer 266 16 6.015% ['fuzz_server']
rfbInitSockets 88 28 31.81% ['fuzz_server']
rfbCloseClient 41 19 46.34% ['fuzz_server']
rfbReadExactTimeout 62 8 12.90% ['fuzz_server']
rfbWriteExact 81 3 3.703% ['fuzz_server']
rfbListenOnTCP6Port 53 27 50.94% ['fuzz_server']
encodingName 60 29 48.33% ['fuzz_server']

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/libvncserver/src/common/minilzo.c [] []
/src/libvncserver/src/libvncserver/sockets.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/ws_decode.c [] []
/src/libvncserver/src/libvncserver/zrleoutstream.c ['fuzz_server'] []
/src/libvncserver/src/libvncserver/tableinit24.c [] []
/src/libvncserver/src/libvncserver/rre.c [] []
/src/libvncserver/test/fuzz_server.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/common/vncauth.c ['fuzz_server'] []
/src/libvncserver/src/libvncserver/zrlepalettehelper.c [] []
/src/libvncserver/src/libvncserver/auth.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/tableinitcmtemplate.c [] []
/src/libvncserver/src/libvncserver/cursor.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/cargs.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/ultra.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/zlib.c [] []
/src/libvncserver/src/common/zywrletemplate.c [] []
/src/libvncserver/src/libvncserver/translate.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/main.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/common/crypto_openssl.c [] []
/src/libvncserver/src/libvncserver/zrleencodetemplate.c [] []
/src/libvncserver/src/libvncserver/rfbserver.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/corre.c [] []
/src/libvncserver/src/libvncserver/tight.c ['fuzz_server'] []
/src/libvncserver/src/libvncserver/hextile.c [] []
/src/libvncserver/src/common/base64.c [] []
/src/libvncserver/src/libvncserver/httpd.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/rfbregion.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/tabletrans24template.c [] []
/src/libvncserver/src/libvncserver/tabletranstemplate.c [] []
/src/libvncserver/src/common/sockets.c ['fuzz_server'] []
/src/libvncserver/src/libvncserver/scale.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/zrle.c ['fuzz_server'] ['fuzz_server']
/usr/include/x86_64-linux-gnu/bits/byteswap.h [] []
/src/libvncserver/src/libvncserver/websockets.c [] []
/src/libvncserver/src/common/turbojpeg.c ['fuzz_server'] []
/src/libvncserver/src/libvncserver/stats.c ['fuzz_server'] ['fuzz_server']
/src/libvncserver/src/libvncserver/rfbssl_openssl.c ['fuzz_server'] []
/src/libvncserver/src/libvncserver/tableinittctemplate.c [] []

Directories in report

Directory
/src/libvncserver/src/libvncserver/
/usr/include/x86_64-linux-gnu/bits/
/src/libvncserver/test/
/src/libvncserver/src/common/

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_server fuzzerLogFile-0-oC6lmXTuE3.data fuzzerLogFile-0-oC6lmXTuE3.data.yaml fuzz_server.covreport