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MySQL UDF Multiple Vulnerabilities (Directory Traversal, DoS, Arbitrary
Library Including, Buffer Overflow)
------------------------------------------------------------------------
SUMMARY
User-defined functions in MySQL allow a user in the database to call
binary libraries on the operating system. Creating a user-defined function
requires insert privileges on the mysql.func table. The lack of proper
length validation allow attackers to execute arbitrary code using MySQL
UDL. Improper directory separator checking, allow attacker to perform
directory traversal using MySQL UDL. The lack of proper checking allow
attackers to cause a denial of service or load arbitrary library with
MySQL UDL.
DETAILS
Vulnerable Systems:
* MySQL version 4.0.25
* MySQL version 4.1.13
* MySQL version 5.0.7-beta
Buffer Overflow:
The init_syms() function uses an unsafe string function to copy a user
specified string into a stack based buffer. Due to improper sanitation
this buffer is able to be overflowed, overwriting portions of the stack.
This allows an attacker to write 14 bytes of arbitrary data and 8 bytes of
hard coded data <beyond the end of the buffer> beyond the end of the
buffer.
The format of the CREATE FUNCTION statement is as follows:
CREATE FUNCTION function_name RETURNS type SONAME "library_name"
User specified input to the "function_name" field is limited to 64
characters. If this library can be successfully loaded by the operating
system, control is then passed to init_syms(). This will attempt to copy
the user string into a buffer 50 bytes in length. Hard coded strings are
then copied onto the end of this string. In some older versions of MySQL
this can be used to gain complete control over the EIP or copy attacker
specified data to an arbitrary location.
One issue of concern is because this buffer is owned by the calling
function, in an environment with a stack that grows upwards, it may be
possible to overwrite the EIP return or other sensitive values.
Exploiting this vulnerability would require the ability to create
user-defined functions. This is not typically granted to untrusted users,
however given this vulnerability you should understand the ramifications
of granting the ability to create user-defined functions.
Arbitrary Library Including:
MySQL attempts to filter execution of arbitrary libraries by requiring any
UDF libraries to have either XXX_deinit() or XXX_init() functions defined.
This is intended to prevent an attacker from including any libraries that
were not specifically programmed to work with MySQL. Unfortunately this
function naming convention is relatively common and default libraries may
have these functions defined.
For instance, the "jpeg1x32.dll" and "jpeg2x32.dll" libraries, included by
default with Windows 2000 have these functions defined.
This allows an attacker to load the jpeg_cmp() function from
"jpeg1x32.dll" and the jpeg_decmp() function from "jpeg2x32.dll". When
either of these functions is called, the MySQL daemon will crash due to
improper argument passing.
Both the jpeg_cmp_init() and jpeg_decmp_init() functions assumes there are
6 arguments waiting for it on the stack. One of these, Arg 6 (EBP+0x1C) is
assumed to be a pointer to a memory location. Areas of the memory past
this pointer are later overwritten by other arguments passed to this
function. Due to the fact that Arg 4 (EBP+0x14) through Arg 6 (EBP+0x1C)
are not used prior to this call, it may be possible to pollute the stack
and overwrite arbitrary memory locations with attacker supplied values.
Although this is a Windows specific example, it is possible that other
operating systems are affected.
Exploiting this vulnerability would require the ability to create
user-defined functions. This is not typically granted to untrusted users,
however given this vulnerability you should understand the ramifications
of granting the ability to create user-defined functions.
DoS:
If an attacker asks a Windows based MySQL server to load an invalid
library file the application will hang until a dialog box is acknowledged
on the server. By requesting one of the many non-library files included in
the PATH by default on Windows installations a
server will be effectively halted. This is due to the fact that the
Windows function LoadLibraryEx() will block when loading an invalid
library file with the following message:
"The application or DLL XXXX is not a valid Windows image. Please check
this against your installation diskette."
It should be noted that this is a Windows specific issue; other operating
systems are not likely to be affected.
An attacker attempting to exploit this issue must have insert privileges
on the mysql.func table. This is a high level of privilege that is not
normally given to untrusted users.
Directory Traversal:
The problem exists in the fact that MySQL only uses the forward slash (/)
as a path separator. Windows machines use the backslash (\) character to
separate directories in paths. This allows an attacker to bypass directory
traversal checks and include arbitrary files.
This may allow an attacker to execute arbitrary code if they are able to
drop a file either through FILE privileges, or other attacks on MySQL or
other programs.
It should be noted that this is a Windows specific issue; other operating
systems are not likely to be affected.
Exploiting this vulnerability would require the ability to create
user-defined functions. This is not typically granted to untrusted users,
however given this vulnerability you should understand the ramifications
of granting the ability to create user-defined functions.
Vendor Status:
The vendor has released patches for MySQL versions 4.0.25, 4.1.13 and
5.0.7-beta: <http://dev.mysql.com/downloads/>
http://dev.mysql.com/downloads/
ADDITIONAL INFORMATION
The information has been provided by <mailto:shatter@appsecinc.com> Team
SHATTER.
The original article can be found at:
<http://www.appsecinc.com/resources/alerts/mysql/2005-001.html>
http://www.appsecinc.com/resources/alerts/mysql/2005-001.html,
<http://www.appsecinc.com/resources/alerts/mysql/2005-003.html>
http://www.appsecinc.com/resources/alerts/mysql/2005-003.html,
<http://www.appsecinc.com/resources/alerts/mysql/2005-002.html>
http://www.appsecinc.com/resources/alerts/mysql/2005-002.html
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