first: do not top-post if you get a reply below second: in the context of suhosin "when mistakes get made by such a person, they are hidden away rather than honestly reported" is bullshit at it's best
* look at the disclosure below
* look at the author
* look at the way it was made
if only 10% of developers would work like Stefan most software
out there would be much better as it is and was all the last years
and if someone has this attitude and knowledge is see no single
problem and understand fully that he is frustrated
_______________
Author: Stefan Esser [stefan.esser[at]sektioneins.de]
Disclosure Timeline:
12. January 2012 - Vulnerability was found during an internal audit
14. January 2012 - Vulnerability was fixed in the source code
19. January 2012 - Public Disclosure
Am 06.02.2012 16:23, schrieb Michael Morris:
> I don't think so. My experience with the attitude he has shown is, when
> mistakes get made by such a person, they are hidden away rather than
> honestly reported. To paraphrase a line from Harry Potter - brilliant
> people don't make many mistakes, but the ones they make tend to be large
> and very damaging.
>
> Security is trust. Given what I have seen I do not trust Stefan to report
> any vulnerabilities created in PHP by Sushonin in a timely manner. I do not
> believe he has the humility necessary to own up to a mistake. Since he is
> that project's only caretaker, I cannot trust the code. If I do not trust
> it, I don't run it.
>
> On Mon, Feb 6, 2012 at 10:15 AM, Reindl Harald <h.rei...@thelounge.net>wrote:
>
>> if your make technical decisions especially security ones by
>> "The character displayed by Stefan" you are maybe doing the
>> wrong job!
-------- Original-Nachricht --------
Betreff: Advisory 01/2012: Suhosin PHP Extension Transparent Cookie Encryption
Stack Buffer Overflow
Datum: Thu, 19 Jan 2012 17:18:23 +0100
Von: Stefan Esser <stefan.es...@sektioneins.de>
An: Full-Disclosure <full-disclos...@lists.grok.org.uk>, Bugtraq
<bugt...@securityfocus.com>
SektionEins GmbH
www.sektioneins.de
-= Security Advisory =-
Advisory: Suhosin PHP Extension Transparent Cookie Encryption Stack
Buffer Overflow
Release Date: 2012/01/19
Last Modified: 2012/01/19
Author: Stefan Esser [stefan.esser[at]sektioneins.de]
Application: Suhosin Extension <= 0.9.32.1
Severity: A possible stack buffer overflow in Suhosin extension's
transparent cookie encryption that can only be triggered
in an uncommon and weakened Suhosin configuration can lead
to arbitrary remote code execution, if the FORTIFY_SOURCE
compile option was not used when Suhosin was compiled.
Risk: Medium
Vendor Status: Suhosin Extension 0.9.33 was released which fixes this
vulnerability
Reference: http://www.suhosin.org/
https://github.com/stefanesser/suhosin
Overview:
Quote from http://www.suhosin.org
"Suhosin is an advanced protection system for PHP installations.
It was designed to protect servers and users from known and
unknown flaws in PHP applications and the PHP core. Suhosin comes
in two independent parts, that can be used separately or in
combination. The first part is a small patch against the PHP
core, that implements a few low-level protections against
buffer overflows or format string vulnerabilities and the second
part is a powerful PHP extension that implements all the other
protections.."
During an internal audit of the Suhosin PHP extension, which is
often confused with the Suhosin PHP Patch, although they are not
the same, a possible stack based buffer overflow inside the
transparent cookie encryption feature was discovered.
If successfully exploited this vulnerability can lead to arbitrary
remote code execution. However further investigation into the
vulnerability revealed that it can only be triggered if the admin
has not only activated transparent cookie encryption, but also
explicitly disabled several other security features of Suhosin.
In addition to that remote exploitation requires a PHP application
that puts unfiltered user input into a call to the header()
function that sends a Set-Cookie header.
Furthermore most modern unix systems compile the Suhosin extension
with the FORTIFY_SOURCE flag, which will detect the possible buffer
overflow and abort execution before something bad can happen.
Details:
The transparent cookie encryption of Suhosin is disabled by default
because it stops applications using JavaScript to access cookies,
which would break these applications. In order to activate it an
admin has to enable this feature in the configuration file:
suhosin.cookie.encrypt = On
Once activated all incoming cookies will be decrypted and all
outgoing Set-Cookie HTTP headers will be rewritten to only contain
encrypted data. When this happens the following code of Suhosin
extension will be triggered.
char *suhosin_encrypt_single_cookie(char *name, int name_len, char
*value, int value_len, char *key TSRMLS_DC)
{
char buffer[4096];
char buffer2[4096];
char *buf = buffer, *buf2 = buffer2, *d, *d_url;
int l;
if (name_len > sizeof(buffer)-2) {
buf = estrndup(name, name_len);
} else {
memcpy(buf, name, name_len);
buf[name_len] = 0;
}
...
if (strlen(value) <= sizeof(buffer2)-2) {
memcpy(buf2, value, value_len);
buf2[value_len] = 0;
} else {
buf2 = estrndup(value, value_len);
}
The problem with this code is that the second call to mempcy()
uses strlen() to check if there is enough buffer space but
uses the variable value_len to determine the amount of bytes
to copy. The problem is that there could be a NUL byte inside
the value of the cookie, which will result in a stack based
buffer overflow. While the same code can also be found inside
the suhosin_decrypt_single_cookie() function the problem cannot
be exploited, because in that case there cannot be a NUL byte.
To understand the limited impact of this vulnerability it is
important to know that NUL bytes are not allowed inside HTTP
headers in a default Suhosin installation. In order to be
vulnerable it is therefore required that the admin explicitly
weakened security by disabling the HTTP response splitting
protection of Suhosin by using the following configuration:
suhosin.multiheader=On
The next thing to know is that PHP applications normally use
the functions setcookie() and setrawcookie() to set cookies.
Both functions are however not affected by the problem
because both functions will eliminate a possible NUL byte
when constructing the Set-Cookie header. Therefore the only
way to trigger this vulnerability is to call the header() function
directly with a "Set-Cookie" header and put unfiltered user
input into the cookie value. This is very uncommon in normal
PHP applications.
In addition to that the default configuration of Suhosin will not
allow NUL bytes in user input. Therefore in order to trigger the
vulnerability remotely the user input must have been double
decoded or the admin must have weakened the installation once
again by disabling the protection against NUL bytes. This can be
done by changing the configuration to.
suhosin.request.disallow_nul=Off
suhosin.get.disallow_nul=Off
suhosin.post.disallow_nul=Off
suhosin.cookie.disallow_nul=Off
Finally even if the vulnerability is triggerable from remote it
depends on the compilation of the Suhosin extension if the bug
can be abused. Most modern unix systems will compile the Suhosin
extension with the FORTIFY_SOURCE compile option, which will
detect the buffer overflow before it actually happens and abort
execution.
If either suhosin.multiheader or suhosin.cookie.encrypt are set
to "off" in your configuration than you are safe from remote
attacks. In addition to that the default configuration of
suhosin.perdir disallows to set these variables from .htaccess
which also provides some protection against local attackers.
Proof of Concept:
Locally the problem can be reproduced by the following PHP code:
<?php header("Set-Cookie: x=xxx".chr(0).str_repeat("A",10000));
If this piece of code does not affect your PHP process at all then
your current configuration is safe. Otherwise it depends if the
Suhosin extension was compiles with the FORTIFY_SOURCE option.
Disclosure Timeline:
12. January 2012 - Vulnerability was found during an internal audit
14. January 2012 - Vulnerability was fixed in the source code
19. January 2012 - Public Disclosure
Recommendation:
It is recommended to upgrade to the latest version of Suhosin
extension, which can be downloaded at:
http://www.suhosin.org
The latest development version of the Suhosin extension can always
be found at:
https://github.com/stefanesser/suhosin
CVE Information:
The Common Vulnerabilities and Exposures project (cve.mitre.org) has
not assigned a name to this vulnerability.
Copyright 2012 SektionEins GmbH. All rights reserved.
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