Pamspy - Credentials Dumper For Linux Using eBPF

Pamspy – Credentials Dumper For Linux Using eBPF

pamspy leverage eBPF technologies to achieve an equivalent work of 3snake.

It will track a particular userland function inside the PAM (Pluggable Authentication Modules) library, used by many critical applications to handle authentication like:

  • sudo
  • sshd
  • passwd
  • gnome
  • x11
  • and many other …

How to launch?

pamspy is built as a static binary without any dependencies, and available on the release page.

Usage: pamspy [OPTION...]
pamspy

Uses eBPF to dump secrets use by PAM (Authentication) module
By hooking the pam_get_authtok function in libpam.so

USAGE: ./pamspy -p $(/usr/sbin/ldconfig -p | grep libpam.so | cut -d ' ' -f4) -d /var/log/trace.0

-d, --daemon=PATH TO OUTPUT CREDENTIALS
Start pamspy in daemon mode and output in the file
passed as argument
-p, --path=PATH Path to the libpam.so file
-r, --print-headers Print headers of the program
-v, --verbose Verbose mode
-?, --help Give this help list
--usage Give a short usage message
-V, --version Print program version

Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.

Report bugs to .

As pamspy rely on libpam, we have to set the path where libpam is installed on your distribution. To find where libpam is installed you can run the following command :

> /usr/sbin/ldconfig -p | grep libpam.so | cut -d ' ' -f4
/lib/x86_64-linux-gnu/libpam.so.0

Once you get the path you can launch pamspy :

> ./pamspy -p /lib/x86_64-linux-gnu/libpam.so.0

An easy way to launch pamspy is to use the following command :

> ./pamspy -p $(/usr/sbin/ldconfig -p | grep libpam.so | cut -d ' ' -f4)

pamspy can also be started as a daemon by providing an output file where credentials will be written:

./pamspy -p $(/usr/sbin/ldconfig -p | grep libpam.so | cut -d ' ' -f4) -d /tmp/credentials

How to build?

To build the static binary, we need third-party program. For eBPF we need clang to compile the C code into eBPF CO-RE code. We also rely on bpftool to create a skeleton from ebpf program to include it in our userland program. Then we need also libelf to find the correct symbol in libpam.

sudo apt install make clang-11 gcc libelf-dev bpftool

Then just build!

git clone https://github.com/citronneur/pamspy --recursive
cd pamspy/src
make

How does It works?

pamspy will load a userland return probe eBPF program to hook the pam_get_authtok function from libpam.so. PAM stands for “Pluggable Authentication Modules”, and have a flexible design to manage a different kind of authentication on Linux.

Each time an authentication process tries to check a new user, It will call pam_get_authtok, and will be here to dump the content of the critical secrets!

Easy! Enjoy!

Credits and references

Thanks to @blendin for 3snake tool !!!

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