Remote code execution in Asus router firmware

by martinp • 12 years ago

125 41 12 years ago

rdtsc2• 12 years ago

There is also a project that provides an open firmware for some of the vulnerable Asus routers:

https://code.google.com/p/rt-n56u/

It seems to be active. I've been thinking of switching to it from a stock rt-n56u. Anyone have any experience using this firmware?

martinp• 12 years ago

I haven't tried that one. I'm using asuswrt-merlin [0], which is another fork based on the official Asus sources.

It's very similar to the original firmware, but with a few extra bug fixes and features. Asus occasionally backports some of the bug fixes to the official firmware. The vulnerable feature has been disabled in the latest version. [1]

[0] https://github.com/RMerl/asuswrt-merlin

[1] http://forums.smallnetbuilder.com/showthread.php?t=21774

vader1• 12 years ago

+1 for asuswrt-merlin. It's the Cyanogenmod of the router world: the stability and speed of officially supported drivers, with the added flexibility and freedom of a custom firmware.

ThreeAs• 12 years ago

That doesn't seem to be on the RT-56U which the OP has.

mscrivo2• 12 years ago

Why not use a good Tomato build? This is my favourite at the moment and gets updated quite frequently:

http://tomato.groov.pl/

rdtsc2• 12 years ago

Saw that one, but my router was not in the list of supported ones.

openwrtuser1• 12 years ago

OpenWrt[1] supports many devices, too, and has a strong emphasis on free/open source software. (Tomato uses a proprietary GUI.)

The rt-n56u appears to have preliminary support. [2]

[1] http://wiki.openwrt.org/toh/start [2] http://wiki.openwrt.org/toh/asus/rt-n56u

sk5t• 12 years ago

After great success with Polarcloud's Tomato on the old WRT54G, I really wanted to use tomato on my AC66U, which is on "Tomato by Shibby"'s supported list, but it resolutely refused to run; same story with OpenWRT. Merlin's build seems to be the only reliable choice for Asuswrt, or at least that's my experience.

Freaken3• 12 years ago

Running DD-WRT v24 sp2 on my N66U here. It works like a charm and you can customize the OS all you want since it's Linux-based.

alfiedotwtf• 12 years ago

Any reason you went with DD-WRT instead of OpenWRT (just curious)?

yc10102• 12 years ago

Do you know if its possible to somehow get the 66 to "split" a connection somehow,

For example lets say i have a 100mbit symmetric connection coming in with the 66 siting on the end of it as the home office router, can i somehow dedicate 10mbit of this to be used only by the wired network and remaining 90 available to the wireless

So if someone is downloading/uploading too much it never can use more than lets say 90% of the external wan connection

aselzer• 12 years ago

There is also an OpenWRT version: http://wiki.openwrt.org/toh/asus/rt-n56u

But it doesn't seem very well supported since 2012.

yc10102• 12 years ago

Asus released updated firmware it seems, that was quick!

http://www.asus.com/ie/Networking/RTAC66U/HelpDesk_Download/

uniformlyrandom2• 12 years ago

No update for N56U yet.

2014/11/21

Well, killing a process is the easiest workaround for now, and it should work until we get a patch.

aric• 12 years ago

Warning to users of Asus firmware:

In the Administration > Firmware Upgrade tab, never rely on their [Check] version button. It's consistently inaccurate. It's a long-known (and serious) flaw that's been like this since day one of these products and still to this day. It'll happily report, "The router's current firmware is the latest version.", even if it's months behind in vulnerability fixes. Go to Asus' site for the latest firmware then use the upload option to upgrade. Or, probably better yet, don't use their firmware.

synunlimited• 12 years ago

Thanks for the tip this is exactly what I had to do to get the latest firmware upgrade with the patch.

gcb0• 12 years ago

note to anyone not using openwrt:

you should be using openwrt :)

Alphasite_3• 12 years ago

AsusWRT is pretty great on its own, apart from this bug, and its kept uptodate.

etcet• 12 years ago

Worst case is that all publicly accessible routers were rooted en-masse within an hour of this announcement. My solution is an offline factory reset and firmware update.

Is there any risk of persistent root on these devices?

dtech• 12 years ago

This issue is nowhere near this serious, it's only exploitable from within the LAN. (http://forums.smallnetbuilder.com/showthread.php?t=21774)

uniformlyrandom2• 12 years ago

In the days of javascript, this is not such a big roadblock. https://developer.chrome.com/apps/app_network

dev314159• 12 years ago

Is this vulnerable from the LAN-side only or from the WAN side?

Aloisius• 12 years ago

LAN-side only according to the Asuswrt-Merlin people: http://forums.smallnetbuilder.com/showthread.php?t=21774

fubarred• 12 years ago

NSA diode candiate, unfortunately :(

For edge devices, it's a criminal that high security standards are not more pervasive. Though given the nature of retail products, it's not a big surprise even though it is still disappointing. (How many of these boxes even work for longer than 5 minutes without spontaneously rebooting (crashing) or having a xfer rate within an order of magnitude of the channel bandwidth?)

PS: If there were a minimal OpenBSD/(x86|arm) based pfSense-alike project that could be easily themed, minified and plugin-ed, that would rock... and potentially dramatically reduce the attack surface by reducing the duplication of awful embedded web app implementations. (Yes, there are DDWRT and other Linux embedded network gear projects and pfSense (which is great)... OpenBSD for fewer lines of code.) It seems like what might happen going forward because the existing vendor stacks are often terrible and likely expensive for them to maintain. (Kickstarter for hw+sw or enterprise "crowd"-funded perhaps.)

Folks requesting pfSense ARM support: https://forum.pfsense.org/index.php?topic=34707.0

orbitingpluto• 12 years ago

An easy hack for disabling many of these additional "features" is just to overload the port by forwarding it to a non-used IP:port.

This is only really useful for the Internet side of things for standard manufacturer's firmware or if you're using WRT.

For new routers, this is standard practice for me until a WRT option becomes available. Sometimes you can't, I remember not being able to overload something on a Linksys EA6500.

whatthehack22• 12 years ago

Question- Lets say you patched this 'too late' - Would doing a hard reset of the router by holding the reset button of the router actually remove any backdoors/exploits? Or is it the case if someone gets root that backdoor will be persistent forever and your only hope is to get a new router? My understanding is that the factory reset only resets the configuration options and does not physically reimage the OS.

simcop2387• 12 years ago

reuploading the firmware should also work, it usually just reimages the system partition. if you don't know if you trust that you can also go to dd-wrt, openwrt or tomato and once you see that running you know the system partition has been reimaged and should be fine.

whatthehack22• 12 years ago

So simply upgrading the firmware now will remove any existing roots or backdoors?

lunixbochs2• 12 years ago

Would doing a hard reset of the router by holding the reset button of the router actually remove any backdoors/exploits?

This "hard reset" method just resets the nvram configuration to default values. It doesn't touch the kernel/userland portion of flash. Once someone has code running on your router, they can easily update the firmware in place. This means you should at minimum flash your router with a new trusted firmware file from the manufacturer (If you download the new file over HTTP, the malicious code on your router could intercept this download and re-inject itself. The mid/high-end Asus routers should be more than fast enough to proxy all of your HTTP connections.).

Many Asus routers use Broadcom's CFE bootloader. Source is available for CFE version 6.0 (used in the AC66U and newer routers), so custom versions can be created with a slightly lower barrier to entry than binary assembly patches.

It's also fairly trivial to modify existing router firmware images, using tools like binwalk and firmware-mod-kit.

With this in mind, your worst case scenario is:

1. The attacker uploaded a new firmware to your device.

2. It includes a modified bootloader to persist the exploit when you do a firmware upgrade via bootloader.

3. It includes a modified kernel/userland with exploit code, and a feature to hide/preserve the affected areas of flash.

This is a relatively unlikely scenario, but could also be hard to detect without externally dumping your SPI flash chip. It's also hard, but not impossible, for an attacker to exfiltrate information from your network unnoticed at this point. Chances are you don't monitor all of your outbound traffic beyond the router if you're running stock firmware.

Another exfiltration method could involve placing the Broadcom wireless chip into client mode and sending data through a nearby wireless network, or just speaking raw wireless frames which are mostly invisible unless you're specifically monitoring wireless traffic on the same channel. This can be done in a sneaky fashion if your router has dual wireless radios (to do concurrent 2.4ghz and 5ghz) and uses the same SSID for both frequencies. One of the radios can be put into client mode without disrupting connections to the other. It's worth noting you can't run the Broadcom radios I've seen in Asus routers in both client and AP mode (or monitor mode, etc - check the wl command line tool for control) at the same time, which makes this harder.

tux• 12 years ago

Been using > https://code.google.com/p/rt-n56u/ on Asus RT-N56U for more then a year now. No issues at all. This firmware is maintained by "Andy Padavan" Changelog here > http://rt-n56u.googlecode.com/git/changes.eng.txt Latest update was yesterday. You can use Entware package manager to install any of this packages here > http://entware.wl500g.info/binaries/entware/Packages.html

lazyjones• 12 years ago

In case it wasn't obvious: yet another case of shooting yourself in the foot with your amazing C skills... Will people ever learn to avoid this, since 99,9% of all C programmers simply aren't good or meticulous enough to write network-facing code in a safe manner?

ithinkso• 12 years ago

What's the alternative?

Remote code execution in Asus router firmware

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