openwrt

74 Articles

The Meraki AP PCB on a desk, case-less, with three USB-UARTs connected to its pins - one for interacting with the device, and two for monitoring both of the UART data lines.

Flashing Booby-Trapped Cisco AP With OpenWrt, The Hard Way

October 26, 2022 by 48 Comments

Certain manufacturers seriously dislike open-source firmware for their devices, and this particular hack deals with quite extreme anti-hobbyist measures. The Meraki MR33, made by Cisco, is a nice access point hardware-wise, and running OpenWrt on it is wonderful – if not for the Cisco’s malicious decision to permanently brick the CPU as soon as you enter Uboot through the serial port. This AP seems to be part of a “hardware as a service” offering, and the booby-trapped Uboot was rolled out by an OTA update some time after the OpenWrt port got published.

There’s an older Uboot version available out there, but you can’t quite roll back to it and up to a certain point, there was only a JTAG downgrade path noted on the wiki – with its full description consisting of a “FIXME: describe the process” tag. Our hacker, an anonymous user from the [SagaciousSuricata] blog, decided to go a different way — lifting, dumping and modifying the onboard flash in order to downgrade the bootloader, and guides us through the entire process. There’s quite a few notable things about this hack, like use of Nix package manager to get Python 2.7 on an OS which long abandoned it, and a tip about a workable lightweight TFTP server for such work, but the flash chip part caught our eye.

The flash chip is in TSOP48 package and uses a parallel interface, and an iMX6.LL devboard was used to read, modify and flash back the image — hotswapping the chip, much like we used to do with old parallel-interface BIOS chips. We especially liked the use of FFC cables and connectors for connecting the flash chip to the devboard in a way that allows hotswapping – now that we can see it, the TSOP 0.5 mm pitch and 0.5 mm FFC hardware are a match made in heaven. This hack, of course, will fit many TSOP48-equipped devices, and it’s nice to have a toolkit for it in case you don’t have a programmer handy.

In the end, the AP got a new lease of life, now governed by its owner as opposed to Cisco’s whims. This is a handy tutorial for anyone facing a parallel-flash-equipped device where the only way appears to be the hard way, and we’re glad to see hackers getting comfortable facing such challenges, whether it’s parallel flash, JTAG or power glitching. After all, it’s great when your devices can run an OS entirely under your control – it’s historically been that you get way more features that way, but it’s also that the manufacturer can’t pull the rug from under your feet like Amazon did with its Fire TV boxes.

We thank [WifiCable] for sharing this with us!

(Ed Note: Changed instances of “OpenWRT” to “OpenWrt”.)

Bufferbloat, The Internet, And How To Fix It

August 18, 2022 by 48 Comments

There’s a dreaded disease that’s plagued Internet Service Providers for years. OK, there’s probably several diseases, but today we’re talking about bufferbloat. What it is, how to test for it, and finally what you can do about it. Oh, and a huge shout-out to all the folks working on this problem. Many programmers and engineers, like Vint Cerf, Dave Taht, Jim Gettys, and many more have cracked this nut for our collective benefit.

When your computer sends a TCP/IP packet to another host on the Internet, that packet routes through your computer, through the network card, through a switch, through your router, through an ISP modem, through a couple ISP routers, and then finally through some very large routers on its way to the datacenter. Or maybe through that convoluted chain of devices in reverse, to arrive at another desktop. It’s amazing that the whole thing works at all, really. Each of those hops represents another place for things to go wrong. And if something really goes wrong, you know it right away. Pages suddenly won’t load. Your VoIP calls get cut off, or have drop-outs. It’s pretty easy to spot a broken connection, even if finding and fixing it isn’t so trivial.

That’s an obvious problem. What if you have a non-obvious problem? Sites load, but just a little slower than it seems like they used to. You know how to use a command line, so you try a ping test. Huh, 15.0 ms off to Google.com. Let it run for a hundred packets, and essentially no packet loss. But something’s just not right. When someone else is streaming a movie, or a machine is pushing a backup up to a remote server, it all falls apart. That’s bufferbloat, and it’s actually really easy to do a simple test to detect it. Run a speed test, and run a ping test while your connection is being saturated. If your latency under load goes through the roof, you likely have bufferbloat. There are even a few of the big speed test sites that now offer bufferbloat tests. But first, some history. Continue reading “Bufferbloat, The Internet, And How To Fix It” →

This Week In Security: UClibc And DNS Poisoning, Encryption Is Hard, And The Goat

May 6, 2022 by 8 Comments

DNS spoofing/poisoning is the attack discovered by [Dan Kaminski] back in 2008 that simply refuses to go away. This week a vulnerability was announced in the uClibc and uClibc-ng standard libraries, making a DNS poisoning attack practical once again.

So for a quick refresher, DNS lookups generally happen over unencrypted UDP connections, and UDP is a stateless connection, making it easier to spoof. DNS originally just used a 16-bit transaction ID (TXID) to validate DNS responses, but [Kaminski] realized that wasn’t sufficient when combined with a technique that generated massive amounts of DNS traffic. That attack could poison the DNS records cached by public DNS servers, greatly amplifying the effect. The solution was to randomize the UDP source port used when sending UDP requests, making it much harder to “win the lottery” with a spoofed packet, because both the TXID and source port would have to match for the spoof to work.

uClibc and uClibc-ng are miniature implementations of the C standard library, intended for embedded systems. One of the things this standard library provides is a DNS lookup function, and this function has some odd behavior. When generating DNS requests, the TXID is incremental — it’s predictable and not randomized. Additionally, the TXID will periodically reset back to it’s initial value, so not even the entire 16-bit key space is exercised. Not great. Continue reading “This Week In Security: UClibc And DNS Poisoning, Encryption Is Hard, And The Goat” →

IC Shortage Keeps Linux Out Of Phone Charger, For Now

September 29, 2021 by 21 Comments

We’ve been eagerly following the development of the WiFiWart for some time now, as a quad-core Cortex-A7 USB phone charger with dual WiFi interfaces that runs OpenWrt sounds exactly like the sort of thing we need in our lives. Unfortunately, we’ve just heard from [Walker] that progress on the project has been slowed down indefinitely by crippling chip shortages.

At this point, we’ve all heard how the chip shortage is impacting the big players out there. It makes sense that automakers are feeling the pressure, since they are buying literally millions of components at a clip. But stories like this are a reminder that even an individual’s hobby project can be sidelined by parts that are suddenly 40 times as expensive as they were when you first put them in your bill of materials.

The new miniature compute board.

In this particular case, [Walker] explains that a power management chip you could get on DigiKey for $1.20 USD a few months ago is now in such short supply that the best offer he’s found so far is $49.70 a pop from an electronics broker in Shenzhen. It sounds like he’s going to bite the bullet and buy the four of them (ouch) that he needs to build a working prototype, but obviously it’s a no go for production.

Luckily, it’s not all bad news. [Walker] has made some good progress on the power supply board, which will eventually join the diminutive computer inside the USB charger enclosure. Part of the trick is that the device is still supposed to be a functional USB charger, so in addition to 5 VDC for the output port, the power supply also needs to produce 1.1 V, 1.35 V, 2.5 V, 3.0 V, and 3.3 V for the computer. We’re glad to see he’s taking the high road with his mains circuitry, making sure to use UL listed components and maintaining proper isolation.

When we last checked in on the WiFiWart back in July, [Walker] had already managed to boot Linux on his over-sized prototype board. Now he’s got PCBs in hand that look far closer to the final size and shape necessary to tuck them into a phone charger. It’s a shame that the parts shortage is slowing down progress, but we’re confident we’ll at least get to see a one-off version of the WiFiWart powered up before the year is out.

This Week In Security: Ghoscript In Imagemagick, Solarwinds, And DHCP Shenanigans

September 10, 2021 by 3 Comments

A PoC was just published for a potentially serious flaw in the Ghostscript interpreter. Ghostscript can load Postscript, PDF, and SVG, and it has a feature from Postscript that has been a continual security issue: the %pipe% command. This command requests the interpreter to spawn a new process — It’s RCE as part of the spec. This is obviously a problem for untrusted images and documents, and Ghostscript has fixed security vulnerabilities around this mis-feature several times over the years.

This particular vulnerability was discovered by [Emil Lerner], and described at ZeroNights X. That talk is available, but in Russian. The issue seems to be a bypass of sorts, where the pipe command appears to be working in the /tmp/ directory, but a simple semicolon allows for an arbitrary command to be executed. Now why is this a big deal? Because ImageMagick uses Ghostscript to open SVG images by default on some distributions, and ImageMagick is often used for automatically resizing and converting images for web sites. In [Emil]’s presentation, he uses this flaw as part of an attack chain against three different companies.

I was unable to reproduce the flaw on my Fedora install, but I haven’t found any notice of it being fixed in the Ghostscript or Imagemagick changelogs either. It’s unclear if this problem has already been fixed, or if this is a true 0-day for some platforms. Either way, expect attackers to start trying to make use of it.

Continue reading “This Week In Security: Ghoscript In Imagemagick, Solarwinds, And DHCP Shenanigans” →

Teardown: Creality Wi-Fi Box

December 28, 2020 by 57 Comments

Creality, makers of the Ender series of 3D printers, have released a product called Wi-Fi Box meant to cheaply add network control to your printer. Naturally I had to order one so we could take a peek, but this is certainly not a product review. If you’re looking to control your 3D printer over the network, get yourself a Raspberry Pi and install Gina Häußge’s phenomenal OctoPrint on it. Despite what Creality might want you to believe, their product is little more than a poor imitation of this incredible open source project.

Even if you manage to get it working with your printer, which judging by early indications is a pretty big if, it won’t give you anywhere near the same experience. At best it’ll save you a few dollars compared to going the DIY route, but at the cost of missing out on the vibrant community of plugin developers that have helped establish OctoPrint as the defacto remote 3D printing solution.

That being said, the hardware itself seems pretty interesting. For just $20 USD you get a palm-sized Linux computer with WiFi, Ethernet, a micro SD slot, and a pair of USB ports; all wrapped up in a fairly rugged enclosure. There’s no video output, but that will hardly scare off the veteran penguin wrangler. Tucked in a corner and sipping down only a few watts, one can imagine plenty of tasks this little gadget would be well suited to. Perhaps it could act as a small MQTT broker for all your smart home devices, or a low-power remote weather station. The possibilities are nearly limitless, assuming we can get into the thing anyway.

So what’s inside the Creality Wi-Fi Box, and how hard will it be to bend it to our will? Let’s take one apart and find out.

Continue reading “Teardown: Creality Wi-Fi Box” →

Hacking A Netgear Router

October 7, 2020 by 7 Comments

Have you ever wanted to watch someone reverse engineer a piece of hardware and pick up some tips? You can’t be there while [Jeremy] tears open a Netgear N300 router, but you can see his process step by step in some presentation charts, and you’ll get a few ideas for the next time you want to do something like this.

The first part of the presentation might be a little basic for most Hackaday readers, but presumably, the intended audience might not know much about soldering or multimeters. But we enjoyed the methodology used to work out the UART pins on the board. We would have read the baud rate with the scope, which [Jeremy] does, but he also mentions a script to work it out and create a minicom profile that looked interesting.

Continue reading “Hacking A Netgear Router” →