[plug] Fwd: UNIX - Multiple MySQL Vulnerabilities (COM_TABLE_DUMP, COM_CHANGE_USER, read_rows, read_one_row)

[Steve Grasso]

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  Multiple MySQL Vulnerabilities (COM_TABLE_DUMP, COM_CHANGE_USER,
read_rows, read_one_row)
------------------------------------------------------------------------


SUMMARY

e-Matters have discovered two flaws within the MySQL server that can be
used by any MySQL user to crash the server. Furthermore one of the flaws
can be used to bypass the MySQL password check or to execute arbitrary
code with the privileges of the user running MySQLd.

e-Matters have also discovered an arbitrary size heap overflow within the
MySQL client library and another vulnerability that allows to write '\0'
to any memory address. Both flaws could allow DOS attacks against or
arbitrary code execution within anything linked against libmysqlclient.

DETAILS

Vulnerable systems:
 * MySQL version 3.23.53a and prior
 * MySQL version 4.0.5a and prior

Immune systems:
 * MySQL version 3.23.54

While auditing the MySQL sourcetree e-Matters discovered several bugs
within the MySQL client and server that are listed below:

+++ SERVER +++ COM_TABLE_DUMP - Signed Integer Vulnerability
When handling the COM_TABLE_DUMP package MySQL < 4.x takes two chars from
the packet, casts them directly to unsigned integers and uses them as
length parameters for memcpy. Obviously negative values within the chars
will turn into very big unsigned numbers. Because this is a heap to heap
copy operation and there is no memory allocating function within the
SIGSEGV handler we strongly believe this bug can only be used for denial
of service attacks. Depending on the packet MySQLd will directly crash or
hang in an endless loop of segmentation faults. This was tested against
Windows, Linux and FreeBSD systems.

+++ SERVER +++ COM_CHANGE_USER - Password Length Vulnerability
In February 2000 Robert van der Meulen discovered a flaw within the main
password authentication system of MySQL: The MySQL challenge response
algorithm creates an expected response with exactly the length of the
response provided by the client. So if the client sends only a one char
response MySQL will check only one byte. But this means it is possible to
give the correct response with only 32 tries (because the character set is
only 32 characters big). When this bug was fixed in 2000 the MySQL authors
simply added a check in the server that the response must be 8 chars long.
However they forgot to add this check to the COM_CHANGE_USER command, too.
So it is still possible for an attacker with a valid MySQL-account to
compromise the other accounts that are allowed to login from the same
host. For a local user this means he can break into the MySQL root account
and so compromise all databases. This is especially dangerous in a shared
environment or if the root user is allowed to login from other hosts than
localhost. While the attacker can supply a one byte response to break into
the other accounts he can also send an oversized one. If the response is
longer than 16 chars the internal created expected answer overflows a
stack buffer. If the response is long enough it is possible to overwrite
the saved instruction pointer with bytes that are generated by the random
number generator of the password verification algorithm. While this sounds
hard or impossible to exploit, we successfully exploited this bug on
e-Matter's Linux machines. Due to the fact that MySQL restarts on crash
you have unlimited tries. Because of the limited set of characters
generated by the random number generator we strongly believe that this bug
is not exploitable on Windows, because it is not possible to overwrite the
instruction pointer with valid controllable addresses.

+++ CLIENT +++ libmysqlclient read_rows Overflow
When the MySQL client library receives answer rows from the server it
wants to copy the answers into another buffer. Therefore it loops through
the returned fields and copies them to the other location. This is done
without actually checking if the stored field sizes are within the
destination buffer boundaries. Additionally there is also a terminating
'\0' added to the end of all fields without checking for enough space
within the destination buffer. Due to the fact that this bug gets already
triggered by a simple SELECT query anything that is linked against
libMySQL is potentially vulnerable. Due to the nature of this bug it is
trivial to use it as denial of service attack against the client
applications (A negative field size will do the job). If it possible to
use this overflow to execute code on the client system is different from
application to application. It depends mainly on the fact if malloc()
overflows are exploitable on that particular system and if the application
allows enough control over the heap structure by triggering different
execution paths.

+++ CLIENT +++ libmysqlclient read_one_row Byte Overwrittes
When the MySQL client library fetches one row from the MySQL server it
loops through the fields to remember pointers to the field values. The
field sizes are trusted and not checked against out of boundary
conditions. After remembering the pointer the previous field gets zero
terminated. A malformed packet can supply any field size and so overwrite
some arbitrary memory address with a '\0'. An invalid address will of
course crash the client. Because the address that is written to is
arbitrary (maybe hard to supply because it must be supplied as delta) all
clients that make use of fetching the answer row by row are most probably
vulnerable to arbitrary code execution exploits.

Finally it must be mentioned that an attacker can of course use a
combination of the described attacks to break into a system or to get
access to privileges he normaly does not own. f.e. it is possible for a
local user to crash the server with the COM_TABLE_DUMP bug (if he cannot
takeover the root account with the COM_CHANGE_USER bug) and then bind a
fake server to the MySQL port 3306. And with a fake server he can exploit
the libmysqlclient overflow. Another scenario would be an attacker that
tries to exploit his favorite mod_scripting language to takeover the web
server by connecting to an external fake server...

Vendor Response:
03. December 2002 Vendor was contacted by email.
04. December 2002 Vendor informs me that bugs are fixed and that they
started building new packages.
12. December 2002 Vendor has released MySQL 3.23.54 which fixes these
vulnerabilities.

Recommendation:
We suggest anyone using MySQL to upgrade to a new or patched version as
soon as possible.


ADDITIONAL INFORMATION

The original advisory can be downloaded from:
 <http://security.e-matters.de/advisories/042002.html>
http://security.e-matters.de/advisories/042002.html

The information has been provided by  <mailto:s.esser at e-matters.de> Stefan
Esser of e-Matters.



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