Report generation date: 2024-04-23

Project overview: libssh2

High level conclusions

Fuzzers reach 25.56% of cyclomatic complexity.

Fuzzers reach 21.42% of all functions.

Reachability and coverage overview

Functions statically reachable by fuzzers

78 / 364

Cyclomatic complexity statically reachable by fuzzers

882 / 3450

Runtime code coverage of functions

109 / 364

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
ssh2_client_fuzzer	/src/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc	104	419	13	13	2321	942	ssh2_client_fuzzer.cc

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	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: ssh2_client_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 0 203 38.8%

gold [1:9] 24 4.59%

yellow [10:29] 13 2.49%

greenyellow [30:49] 2 0.38%

lawngreen 50+ 280 53.6%

All colors 522 100

Color	Runtime hitcount	Callsite count	Percentage
red	0	203	38.8%
gold	[1:9]	24	4.59%
yellow	[10:29]	13	2.49%
greenyellow	[30:49]	2	0.38%
lawngreen	50+	280	53.6%
All colors	522	100

Fuzz blockers

The followings are the branches where fuzzer fails to bypass.

Unique non-covered Complexity	Unique Reachable Complexities	Unique Reachable Functions	All non-covered Complexity	All Reachable Complexity	Function Name	Function Callsite	Blocked Branch
960	2621	15 : View List ['strlen', '_libssh2_sha_algo_ctx_init', '_libssh2_htonu32', '_libssh2_packet_require', '_libssh2_transport_send', '_libssh2_bn_from_bin', '_libssh2_dh_secret', 'BN_num_bits', '_libssh2_sha_algo_ctx_final', '_libssh2_debug_low', 'explicit_bzero', '_libssh2_sha_algo_value_hash', 'BN_bn2bin', '_libssh2_get_string', '_libssh2_sha_algo_ctx_update']	968	3005	diffie_hellman_sha_algo	call site: 00000	/src/libssh2/src/kex.c:517
704	2668	19 : View List ['_libssh2_htonu32', '_libssh2_ecdh_gen_k', '_libssh2_get_string', 'BN_bn2bin', 'strlen', '_libssh2_sha512_init', '_libssh2_sha512_update', '_libssh2_packet_require', '_libssh2_transport_send', 'BN_num_bits', '_libssh2_sha384_update', 'explicit_bzero', '_libssh2_debug_low', '_libssh2_sha384_final', '_libssh2_sha512_final', '_libssh2_sha256_init', '_libssh2_sha256_update', '_libssh2_sha256_final', '_libssh2_sha384_init']	706	3011	ecdh_sha2_nistp	call site: 00000	/src/libssh2/src/kex.c:1972
70	2002	13 : View List ['strlen', '_libssh2_htonu32', '_libssh2_curve25519_gen_k', '_libssh2_packet_require', '_libssh2_transport_send', '_libssh2_sha256_final', 'BN_num_bits', '_libssh2_debug_low', 'explicit_bzero', '_libssh2_sha256_init', 'BN_bn2bin', '_libssh2_sha256_update', '_libssh2_get_string']	72	2345	curve25519_sha256	call site: 00000	/src/libssh2/src/kex.c:2613
28	47	4 : View List ['_libssh2_calloc', '_libssh2_list_add', '_libssh2_channel_nextid', '_libssh2_debug_low']	28	1690	packet_x11_open	call site: 00403	/src/libssh2/src/packet.c:349
25	44	3 : View List ['_libssh2_list_add', '_libssh2_channel_nextid', '_libssh2_debug_low']	25	1687	packet_authagent_open	call site: 00432	/src/libssh2/src/packet.c:506
17	43	3 : View List ['_libssh2_rsa_new', '_libssh2_eob', '_libssh2_get_string']	17	43	hostkey_method_ssh_rsa_init	call site: 00000	/src/libssh2/src/hostkey.c:102
15	67	3 : View List ['_libssh2_dsa_new', '_libssh2_eob', '_libssh2_get_string']	15	67	hostkey_method_ssh_dss_init	call site: 00000	/src/libssh2/src/hostkey.c:570
11	11	2 : View List ['kex_get_method_by_name', 'strchr']	13	85	kex_agree_kex_hostkey	call site: 00202	/src/libssh2/src/kex.c:3624
11	11	2 : View List ['kex_get_method_by_name', 'strchr']	13	33	kex_agree_hostkey	call site: 00213	/src/libssh2/src/kex.c:3541
11	11	2 : View List ['kex_get_method_by_name', 'strchr']	13	33	kex_agree_crypt	call site: 00224	/src/libssh2/src/kex.c:3703
11	11	2 : View List ['kex_get_method_by_name', 'strchr']	13	33	kex_agree_mac	call site: 00234	/src/libssh2/src/kex.c:3767
11	11	2 : View List ['kex_get_method_by_name', 'strchr']	13	33	kex_agree_comp	call site: 00245	/src/libssh2/src/kex.c:3821

Runtime coverage analysis

Covered functions

110

Functions that are reachable but not covered

35

Reachable functions

104

Percentage of reachable functions covered

66.35%

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
/src/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc	1
global.c	3
../src/openssl.c	3
session.c	16
misc.c	17
kex.c	12
hostkey.c	1
crypt.c	1
mac.c	2
comp.c	1
transport.c	6
packet.c	6
channel.c	7

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	instr count	bb count	cyclomatic complexity	Reachable functions	total cyclomatic complexity	Unreached complexity
`hostkey_method_ssh_ed25519_initPEMFromMemory`	/src/libssh2/src/hostkey.c	5	['struct._LIBSSH2_SESSION ', 'char ', 'size_t', 'char *', 'N/A']	9	89	14	6	123	612	539
`kex_method_ecdh_key_exchange`	/src/libssh2/src/kex.c	2	['struct._LIBSSH2_SESSION ', 'struct.key_exchange_state_low_t ']	28	358	44	17	117	1139	401
`kex_method_curve25519_key_exchange`	/src/libssh2/src/kex.c	2	['struct._LIBSSH2_SESSION ', 'struct.key_exchange_state_low_t ']	28	359	45	17	111	968	215
`kex_method_diffie_hellman_group_exchange_sha1_key_exchange`	/src/libssh2/src/kex.c	2	['struct._LIBSSH2_SESSION ', 'struct.key_exchange_state_low_t ']	28	347	39	16	117	983	207
`_libssh2_pub_priv_keyfile`	/src/libssh2/src/../src/openssl.c	7	['struct._LIBSSH2_SESSION ', 'N/A', 'size_t ', 'N/A', 'size_t ', 'char ', 'char *']	8	164	16	4	121	535	59
`libssh2_channel_read_ex`	/src/libssh2/src/channel.c	4	['struct._LIBSSH2_CHANNEL ', 'int', 'char ', 'size_t']	29	169	33	10	72	739	53
`libssh2_channel_direct_streamlocal_ex`	/src/libssh2/src/channel.c	4	['struct._LIBSSH2_SESSION ', 'char ', 'char *', 'int']	29	101	20	7	75	736	46
`libssh2_poll`	/src/libssh2/src/session.c	3	['struct._LIBSSH2_POLLFD *', 'int', 'size_t']	12	915	111	30	73	731	45
`_libssh2_pem_parse`	/src/libssh2/src/pem.c	7	['struct._LIBSSH2_SESSION ', 'char ', 'char ', 'char ', 'struct._IO_FILE ', 'N/A', 'size_t ']	5	740	98	39	26	120	41
`hostkey_method_ssh_ecdsa_sig_verify`	/src/libssh2/src/hostkey.c	6	['struct._LIBSSH2_SESSION ', 'char ', 'size_t', 'char *', 'size_t', 'N/A']	3	140	20	9	23	73	38

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

Functions statically reachable by fuzzers

182 / 364

Cyclomatic complexity statically reachable by fuzzers

2364 / 3450

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	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/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc

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=['session_free', 'packet_queue_listener', '_libssh2_packet_add', 'packet_x11_open', 'session_startup', 'packet_authagent_open', '_libssh2_kex_agree_instr', '_libssh2_transport_send']

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
hostkey_method_ssh_rsa_init	53	25	47.16%	[]
hostkey_method_ssh_dss_init	40	12	30.0%	[]
libssh2_keepalive_send	31	7	22.58%	['ssh2_client_fuzzer']
kex_agree_kex_hostkey	53	27	50.94%	['ssh2_client_fuzzer']
kex_agree_hostkey	48	22	45.83%	['ssh2_client_fuzzer']
kex_agree_crypt	37	17	45.94%	['ssh2_client_fuzzer']
kex_agree_mac	42	20	47.61%	['ssh2_client_fuzzer']
kex_agree_comp	37	17	45.94%	['ssh2_client_fuzzer']
curve25519_sha256	403	114	28.28%	[]
ecdh_sha2_nistp	405	104	25.67%	[]
diffie_hellman_sha_algo	628	209	33.28%	[]
_libssh2_error_flags	31	15	48.38%	['ssh2_client_fuzzer']
_libssh2_debug_low	53	23	43.39%	['ssh2_client_fuzzer']
packet_queue_listener	170	56	32.94%	['ssh2_client_fuzzer']
packet_x11_open	146	59	40.41%	['ssh2_client_fuzzer']
packet_authagent_open	126	39	30.95%	['ssh2_client_fuzzer']
_libssh2_wait_socket	62	33	53.22%	['ssh2_client_fuzzer']
session_startup	106	39	36.79%	['ssh2_client_fuzzer']
session_free	206	88	42.71%	['ssh2_client_fuzzer']
_libssh2_transport_send	170	70	41.17%	['ssh2_client_fuzzer']
debugdump	47	10	21.27%	['ssh2_client_fuzzer']
fullpacket	108	39	36.11%	['ssh2_client_fuzzer']
send_existing	41	8	19.51%	['ssh2_client_fuzzer']

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/libssh2/src/global.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/misc.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/crypt.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/comp.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/hostkey.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/channel.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/kex.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/bcrypt_pbkdf.c	[]	[]
/src/libssh2/src/keepalive.c	[]	[]
/src/libssh2/src/../src/blowfish.c	[]	[]
/src/libssh2/src/session.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/../src/openssl.c	['ssh2_client_fuzzer']	[]
/src/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/mac.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/transport.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/packet.c	['ssh2_client_fuzzer']	['ssh2_client_fuzzer']
/src/libssh2/src/pem.c	[]	[]

Directories in report

Directory

/src/libssh2/src/../src/
/src/libssh2/src/
/src/libssh2/tests/ossfuzz/

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

ssh2_client_fuzzer fuzzerLogFile-0-uVkL8rJcbP.data fuzzerLogFile-0-uVkL8rJcbP.data.yaml ssh2_client_fuzzer.covreport

Table of contents

Project overview: libssh2

High level conclusions

Reachability and coverage overview

Fuzzers overview

Project functions overview

Fuzzer details

Fuzzer: ssh2_client_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/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc

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