retrace is a versatile security vulnerability / bug discovery tool
through monitoring and modifying the behavior of compiled binaries on
Linux, OpenBSD/FreeBSD/NetBSD (shared object) and macOS (dynamic library).
retrace can be used to assist reverse engineering / debugging
dynamically-linked ELF (Linux/OpenBSD/FreeBSD/NetBSD) and
Mach-O (macOS) binary executables.
Work in a new version of retrace is ongoing, all the documentation is only about retrace v1, early documentation for
retrace v2 is here.
If you want to give it a go despiste the lack of documentation you can enable it in the build using ./configure --enable-v2.
We are Ribose, the secure sharing company. We believe privacy and security form the foundation of liberty.
Our goal is to empower individuals and organizations alike to freely communicate and achieve productivity for the greater good, through our deep security and technology expertise, creating highly-secure products validated to the world’s most stringent requirements and regulations.
We created retrace to aid developers and security researchers to develop better code that leads the world to a better place.
The Ribose retrace team can be reached at retrace@ribose.com. We will answer questions to the best of our efforts.
For platforms with Autotools, the generic way to build and install
retrace is:
$ sh autogen.sh
$ ./configure --enable-tests
$ make
$ make check
$ sudo make installYou need Autotools installed in your system (autoconf, automake,
libtool, make, gcc packages).
OpenSSL library and headers are automatically detected, you can specify
an optional flag --with-openssl=[PATH] (to use a non-standard OpenSSL
installation root).
In order to build tests: run configure script with --enable-tests
flag. To build cmocka tests you can specify an optional flag
--with-cmocka=[PATH] (to use a non-standard cmocka installation root).
By the default retrace is installed in /usr/bin directory.
$ retrace [-f configuration file location] <executable>Configuration file path can be set either in RETRACE_CONFIG
environment variable or by specifying -f [path] command line argument.
Interactive control over retrace can be exercised using cli control feature
over pseudo terminal (currently available on Linux platforms only).
In order to enable the feature, export RETRACE_CLI=1 environment variable.
When enabled, the name of the pseudo device will be printed with a 3 seconds delay during the start up:
RETRACE-INIT [INFO]: cli pts is at: /dev/pts/1After that, a terminal emulator can be connected to that device:
minicom -p /dev/pts/1Hit the main Enter key, and the command menu with prompt will appear:
Welcome to minicom 2.7.1
OPTIONS: I18n
Compiled on Aug 13 2017, 15:25:34.
Port /dev/tty8, 13:10:04
Press CTRL-A Z for help on special keys
Failed to get command id, retry
Retrace command menu
\--------------------
[0] <Main> Say Hi
[1] <Main> Terminate process
Enter command id>>The following are the characteristics of the terminal:
-
Raw mode - no line processing will be performed on the input.
-
Characters are echoed back.
-
Main enter key is used to mark the end of input.
In order to expose interactive commands from your module, use API defined in retrace_cli.h. To register commads use cli_register_command_blk(). To interact with the user use cli_printf() and cli_scanf(). Refer to retrace_main.c for reference.
In its most basic form retrace will just print all calls that are made
(and that are supported by retrace):
$ retrace /usr/bin/id
(2051) geteuid();
(2051) getuid();
(2051) getegid();
(2051) getgid();
(2051) fopen("/etc/passwd", "rce"); [3]
(2051) fclose(3);
(2051) fopen("/etc/group", "rce"); [3]
(2051) fclose(3);
(2051) fopen("/etc/group", "rce"); [3]
(2051) fclose(3);
(2051) fopen("/etc/group", "rce"); [3]
(2051) fclose(3);
uid=1000(test) gid=1000(test) groups=1000(test),10(wheel)
(2051) exit(0);
(2051) fileno(1);
(2051) fclose(1);
(2051) fileno(2);
(2051) fclose(2);The power of retrace lies in its ability to modify the behavior of
the standard system calls in a number of different ways.
This is done using a config file.
An easy example is redirecting the output of the getuid() call:
$ cat retrace.conf
getuid,0
geteuid,0
getegid,0
getgid,0
$ retrace -f retrace.conf /usr/bin/id
(4982) geteuid(); [redirection in effect: '0']
(4982) getuid(); [redirection in effect: '0']
(4982) getegid(); [redirection in effect: '0']
(4982) getgid(); [redirection in effect: '0']
(4982) fopen("/etc/passwd", "rce"); [3]
(4982) fclose(3);
(4982) fopen("/etc/group", "rce"); [3]
(4982) fclose(3);
(4982) fopen("/etc/group", "rce"); [3]
(4982) fclose(3);
(4982) fopen("/etc/group", "rce"); [3]
(4982) fclose(3);
uid=0(root) gid=0(root) groups=0(root)
(4982) exit(0);
(4982) fileno(1);
(4982) fclose(1);
(4982) fileno(2);
(4982) fclose(2);Other useful config file options are listed below.
connect,127.0.0.1,8080,192.168.1.110,9090Will redirect a connect() call from 127.0.0.1:8080 to
192.168.1.110:9090.
fopen,/etc/passwd,/tmp/passwdWill redirect a fopen() call from /etc/passwd to /tmp/passwd.
logtofile,retrace.logWill send the log file to a file rather than stderr. You can configure
log output to write to /dev/null disable logging completely.
SSL_get_verify_result,10Will cause the OpenSSL function SSL_get_verify_result to return any
desired value.
memoryfuzzing,0.05This option will cause a percentage of malloc(), realloc() and
calloc() calls to fail.
The percentage is specified in a number (float) from 0 (no fail) to
1 (all fail). This is useful to discover places in your code where you
are not checking the return value of allocators.
The seed of the random generator can be controlled with the
fuzzingseed,1498729252 option, so that the results are repeatable.
incompleteio,10This option will cause the read() / write() calls to randomly
write/read less bytes than was asked. A common scenario that people
forget to check.
showtimestamp
showcalltime,0.0001These two options will cause a timestamp (since the beginning of the tracing) to be shown and the time a call took if it’s larger than the specified time in float seconds.
logging-global,LOG_GROUP_FILE|LOG_GROUP_MEM,RTR_LOG_LEVEL_ALL
logging-excluded-funcs,free|memcpy|malloc
logging-allowed-funcs,strlen
stacktrace-groups,LOG_GROUP_MEM
stacktrace-disabled-funcs,callocThese options will enable or disable logging options by group or level.
The each group, level or function may be combined by | character.
logging-global,[logging group],[logging level]
groups: LOG_GROUP_ALL,LOG_GROUP_MEM,LOG_GROUP_FILE,LOG_GROUP_NET,LOG_GROUP_SYS,
LOG_GROUP_STR,LOG_GROUP_SSL,LOG_GROUP_PROC
levels: LOG_LEVEL_ALL,LOG_LEVEL_NOR,LOG_LEVEL_ERR,LOG_LEVEL_FUZZ,LOG_LEVEL_REDIRECT
logging-excluded-funcs,[functions list]
logging-allowed-funcs,[functions list]
stacktrace-groups,[logging groups]
stacktrace-disabled-funcs,[functions list]We use the DYLD_INSERT_LIBRARIES environment variable to insert retrace into binaries.
Starting on Mac OS X El Capitan Apple removes the DYLD_INSERT_LIBRARIES variable for
the environment for binaries in system directories. This means you can’t trace system binaries
using retrace by default.
You can disable this behaviour by running csrutil disable and rebooting.
retrace is under heavy development and we are always looking to implement new
and useful features that allows debugging and reverse engineering programs in
new and interesting ways.
Please send feedback and improvement suggestions either as GitHub issues or to retrace@ribose.com.