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-= Security Advisory =-
Advisory: Multiple vulnerabilities within PHP 4/5
Release Date: 2004/12/15
Last Modified: 2004/12/15
Author: Stefan Esser [firstname.lastname@example.org]
Application: PHP4 <= 4.3.9
PHP5 <= 5.0.2
Severity: Several vulnerabilities within PHP allow
local and remote execution of arbitrary code
Vendor Status: Vendor has released bugfixed versions.
PHP is a widely-used general-purpose scripting language that is
especially suited for Web development and can be embedded into HTML.
During the development of Hardened-PHP which adds security hardening
features to the PHP codebase, several vulnerabilities within PHP
were discovered that reach from bufferoverflows, over information
leak vulnerabilities and path truncation vulnerabilities to
safe_mode restriction bypass vulnerabilities.
[01 - pack() - integer overflow leading to heap bufferoverflow ]
Insufficient validation of the parameters passed to pack() can
lead to a heap overflow which can be used to execute arbitrary
code from within a PHP script. This enables an attacker to
bypass safe_mode restrictions and execute arbitrary code with
the permissions of the webserver. Due to the nature of this
function it is unlikely that a script accidently exposes it to
[02 - unpack() - integer overflow leading to heap info leak ]
Insufficient validation of the parameters passed to unpack() can
lead to a heap information leak which can be used to retrieve
secret data from the apache process. Additionally a skilled
local attacker could use this vulnerability in combination with
01 to bypass heap canary protection systems. Similiar to 01 this
function is usually not used on user supplied data within
[03 - safe_mode_exec_dir bypass in multithreaded PHP ]
When safe_mode is activated within PHP, it is only allowed to
execute commands within the configured safe_mode_exec_dir.
Unfourtunately PHP does prepend a "cd [currentdir] ;" to any
executed command when a PHP is running on a multithreaded unix
webserver (f.e. some installations of Apache2). Because the name
of the current directory is prepended directly a local attacker
may bypass safe_mode_exec_dir restrictions by injecting shell-
commands into the current directory name.
[04 - safe_mode bypass through path truncation ]
The safe_mode checks silently truncated the file path at MAXPATHLEN
bytes before passing it to realpath(). In combination with certain
malfunctional implementations of realpath() f.e. within glibc this
allows crafting a filepath that pass the safe_mode check although
it points to a file that should fail the safe_mode check.
[05 - path truncation in realpath() ]
PHP uses realpath() within several places to get the real path
of files. Unfourtunately some implementations of realpath() silently
truncate overlong filenames (f.e. OpenBSD, and older NetBSD/FreeBSD)
This can lead to arbitrary file include vulnerabilities if something
like "include "modules/$userinput/config.inc.php"; is used on such
[06 - unserialize() - wrong handling of negative references ]
The variable unserializer could be fooled with negative references
to add false zvalues to hashtables. When those hashtables get
destroyed this can lead to efree()s of arbitrary memory addresses
which can result in arbitrary code execution. (Unless Hardened-PHP's
memory manager canaries are activated)
[07 - unserialize() - wrong handling of references to freed data ]
Additionally to bug 06 the previous version of the variable
unserializer allowed setting references to already freed entries in
the variable hash. A skilled attacker can exploit this to create
an universal string that will pass execution to an arbitrary
memory address when it is passed to unserialize(). For AMD64 systems
it was even possible to developed a string that directly passes
execution to shellcode contained in the string itself.
It is necessary to understand that these strings can exploit a
bunch of popular PHP applications remotely because they pass f.e.
cookie content to unserialize().
Examples of vulnerable scripts:
- Invision Board
- Woltlab Burning Board 2.x
- Serendipity Weblog
Proof of Concept:
The Hardened-PHP project is not going to release exploits for any
of these vulnerabilities to the public.
The Common Vulnerabilities and Exposures project (cve.mitre.org) has
assigned the name CAN-2004-1018 to issues 01, 02, the name
CAN-2004-1019 to issues 06, 07, the name CAN-2004-1063 to issue 03
and the name CAN-2004-1064 to issues 04, 05.
It is strongly recommended to upgrade to the new PHP-Releases as
soon as possible, because a lot of PHP applications expose the
easy to exploit unserialize() vulnerability to remote attackers.
Additionally we always recommend to run PHP with the Hardened-PHP
pub 1024D/0A864AA1 2004-04-17 Hardened-PHP Signature Key
Key fingerprint = 066F A6D0 E57E 9936 9082 7E52 4439 14CC 0A86 4AA1
Copyright 2004 Stefan Esser. All rights reserved.
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