Tenda firmware (multiple versions) contains hidden authentication backdoor

https://kb.cert.org/vuls/id/213560

by miniBill • 16 days ago

356 118 16 days ago

kb.cert.org

Up and out the back door, any 'ol time.

fusslo• 16 days ago

Tenda is a supplier of home and business network devices such as routers, switches, wireless access points, and video surveillance equipment.

I was unfamiliar with Tenda.

Shenzhen Tenda Technology Co.,Ltd. ( https://www.tendacn.com/us/profile )

Tenda may just rebrand, right? It seems like many chinese brands will either rebrand or have a 'competing' brand with the same internals but different externals. (I have no idea if Tenda does this, I've just seen it previously. Specifically with security cameras)

I wish the authors provided some method for checking this vulnerability other than fw version. It seems like Tenda could just change the password and say "yep! all safe now"

TedDoesntTalk• 16 days ago

I’m in the USA and have a Tenda WiFi usb stick. Not as popular as other brands but they are around

dpacmittal• 15 days ago

Tenda is very popular in Asia, several ISPs use them as their default routers.

userbinator• 15 days ago

It is probably just a brand, like many others, and based on a reference design from the OEM.

I have a small Tenda 5-port gigabit dumb switch. It uses the same switch chip as this TP-Link, just with different branding; even the "SG105" model number is the same:

https://goughlui.com/2022/02/27/unbox-teardown-tp-link-tl-sg...

_puk• 15 days ago

Tenda has been around for quite a few years now. I don't imagine they'll rebrand.

I have an ethernet over power adapter somewhere in a cupboard from perhaps 10 years ago.

Back then it was standard for the admin password to be 'admin'. They'd often even print it on the device itself.

ale42• 15 days ago

the admin password to be 'admin'. They'd often even print it on the device itself.

Yes but aren't you supposed to change that one? The problem with the rzadmin is that it will continue to work even after you change the regular admin one...

puzzlingcaptcha• 15 days ago

I am still using their Powerline adapters and FWIW they have been very reliable.

jamesnorden• 15 days ago

There's claims of it being "the first home-grown router and wireless network device manufacturer in China".

morpheuskafka• 15 days ago

My ex used to work in their sales department lol. But I'd seen them anyway, in the context of cheap unmanaged switches on Amazon. They are not a state owned company or anything so I doubt this is anything too nefarious, likely just absolutely not giving a crap about quality.

greyface-• 16 days ago

The article doesn't disclose the value of "sys.rzadmin.password", but this writeup from 2022 does:

https://boschko.ca/tenda_ac1200_router/

Spoiler: it's "rzadmin". And it looks like there are a bunch of other goodies in the firmware, too.

lemagedurage• 15 days ago

Sounds like a convenience feature for a dev that they forgot to remove before distribution, since it's this poorly hidden.

sph2• 15 days ago

In computer security, never attribute to ignorance that which is adequately explained by malice.

thibaut_barrere• 15 days ago

That backdoor is so up front about it. We might as well call it a frontdoor.

Wololooo2• 15 days ago

I mean, it's 99% sure this was supposed to be a debug feature...

BloondAndDoom• 15 days ago

At that point it’s not even a back door it’s just stupid default root password kind of design which used to be standard in this kind of hardware. Backdoor would at least try to be subtle :)

Asraelite• 15 days ago

Backdoors are often (almost always?) designed to look like incompetence so that there's plausible deniability.

LargoLasskhyfv• 15 days ago

Somehow this reads like German to me. Because "rz" is a common abbreviation of RechenZentrum, meaning DataCenter.

So in English it would be like "dcadmin". Maybe they outsourced it to someone doing "gute Deutsche Wertarbeit", or it's a leftover from some agency having had their fun, or smoke&mirrors from whomever for whichever reasons.

petee• 15 days ago

Nearly 4 years from last notification and the password is the same; either thats real incompetence, or a hilarious power move

drnick12• 16 days ago

And this is why I handroll my own routers/firewalls, using commodity hardware and a Linux distribution.

matltc2• 15 days ago

Looking to do this to get off stock isp leased router. What's your hardware/distro rec?

dhruvrrp• 15 days ago

Use openWrt (https://openwrt.org), and use their hardware list to pick a consumer router with the feature set you need that can be flashed to use openWrt.

drnick12• 15 days ago

Ryzen 5 with a dual 10Gbps NIC, running Debian. Overkill for a router/firewall, but I run other services on the same hardware including an email stack, Podman containers, and small AI model for use within Home Assistant.

I wouldn't buy new hardware. Any modest machine built in the last decade would do. If possible, get a machine with an internal ATX power supply rather than an external brick, they tend to be more reliable.

If all you need is 1Gpbs and WiFi, OpenWrt on consumer hardware is probably enough though.

yabones• 15 days ago

You can use basically any hardware. I've done it with trash-picked laptops and USB ethernet adapters. Best option these days is a N100/N150 mini-pc with multiple NICs onboard, but with the price of everything going up maybe trashpicking will make a return.

https://nbailey.ca/post/router

ikidd2• 15 days ago

Man, I remember doing this in the late 90s with ipchains as the only way to get a router that didn't cost an arm and a leg. Eventually consumer/prosumer routers came out.

What's old is new again.

SuperMouse• 15 days ago

Tenda has good support among OpenWRT.

consp2• 15 days ago

So the next step is a hardware or boot firmware backdoor?

(Good to know it remains useful by using openWRT and doesn't become landfill)

ggm2• 16 days ago

Have used their travel wifi product back when hotel wifi was a strange beast. Wouldn't expect to need it now eSIM and ubiquitous internet travel pricing means the hotel wifi may be the LEAST valid path to access things.

I have a free give-away mikrotik unit in the same price bracket (literally free: they were both conference give-aways) it's physically smaller and it runs what appears to be their mainline code. Say what you like about microtik for quality, they provide pretty much every knob and frob you could want.

VladVladikoff3• 15 days ago

I’m working on a hotel right now. And I’ve gone to great lengths to make the wifi more secure. Everyone on their own VLAN. Separate PPSK for each room. Credentials are randomly generated and not some ridiculous pattern of last name and room number or similar. We built our own custom access control system, with what at the time was the strongest keycards we could find (mifare desfire ev3), I’m really trying to make a hotel who’s security isn’t such a joke.

ggm2• 15 days ago

As long as I can bind more than one device in my room, and as long as I can "see" the devices amongst themselves, I'd love this. I can imagine people who want inter-room access but they can live through proxies offsite. If I want to do in room sharing, I need in room wifi.

Gets hard when you bring "smart" TV's to the table. They're going to need to expose into this system somewhat 'credential-free' but if you do it off MAC address then a determined user could disconnect, find MAC, clone ...

miki123211• 15 days ago

How do you distribute credentials to residents?

My Macbook is permanently locked out of Cox's hotspot system (used in some U.S. hotels) because the password was given to me on a tiny label which I couldn't read as a blind person except through OCR, and the OCR was wrong a few too many times.

jeffbee• 15 days ago

What fun is that? It used to be fun to `net send` little notes to strangers in hotels.

HDBaseT• 15 days ago

The US/Israel would never do such a thing, buy UniFi/Fortinet/Palo Alto!

Gigachad• 15 days ago

There was a meme going round of a network diagram that layers a Chinese firewall behind a US firewall behind a Russian firewall so they can all block each other countries backdoors.

sph2• 15 days ago

https://en.wikipedia.org/wiki/Swiss_cheese_model

ranger_danger• 15 days ago

Not sure if you're joking, but both have already done so. And any US company is subject to secret orders forcing them to implement a backdoor if demanded.

k_g_b_• 15 days ago

They'll have a lot of work to do, if they want to catch up with the amount and rate of "hidden authentication backdoors" all those companies (and also Cisco) have. E.g. https://www.thestack.technology/cisco-hard-coding-passwords-...

matltc2• 15 days ago

My ifconfig is simple: if it's made in Shenzhen, throw it out

riskd• 15 days ago

Yikes

hathym• 15 days ago

I bet more than half of components in all your electronics are made in Shenzhen

daneel_w4• 15 days ago

And that's something very different than a complete product designed from scratch by a Chinese team in Shenzhen.

dhx• 15 days ago

It looks like recent Tenda hardware/firmware is encrypted per below examples, making it harder to audit.

binwalk US_AC10V6.0si_V16.03.62.09_multi_TDE01.bin

  DECIMAL       HEXADECIMAL     DESCRIPTION
  --------------------------------------------------------------------------------
  516           0x204           OpenSSL encryption, salted, salt: 0x436999A39FECA649

binwalk US_BE12ProV1.0mt_V16.03.66.23_TD01.bin

  DECIMAL       HEXADECIMAL     DESCRIPTION
  --------------------------------------------------------------------------------
  516           0x204           OpenSSL encryption, salted, salt: 0x81235B7D4130B6AB

The third attempt I tried was unencrypted, and possibly reveals the problem exists on another model this CVE doesn't list as affected:

binwalk US_W18EV2_kf_V16.01.0.20\(4766\)_HighPower\ \(1\).bin

  DECIMAL       HEXADECIMAL     DESCRIPTION
  --------------------------------------------------------------------------------
  64            0x40            uImage header, header size: 64 bytes, header CRC: 0x95335734, created: 2026-06-16 09:09:35, image size: 2159135 bytes, Data Address: 0x80100000, Entry Point: 0x805F41C0, data CRC: 0x5ABEDB00, OS: Linux, CPU: MIPS, image type: OS Kernel Image, compression type: lzma, image name: "MIPS Tenda Linux-4.14.90"
  128           0x80            LZMA compressed data, properties: 0x6D, dictionary size: 8388608 bytes, uncompressed size: 6947248 bytes
  2159263       0x20F29F        Squashfs filesystem, little endian, version 4.0, compression:xz, size: 8971644 bytes, 847 inodes, blocksize: 1048576 bytes, created: 2026-06-16 08:53:20

Inside is /squashfs-root/webroot_ro/default_ac.cfg which offers:

  sys.rzadmin.username=rzadmin
  sys.rzadmin.password=cnphZG1pbg==  (ed: base64 decoded: rzadmin)
  sys.guest.username=guest
  sys.guest.password=Z3Vlc3Q=  (ed: base64 decoded: guest)

And /squashfs-root/webroot_ro/default_router.cfg which offers:

  sys.rzadmin.username=rzadmin
  sys.rzadmin.password=cnphZG1pbg==  (ed: base64 decoded: rzadmin)

From what I can see quickly (I haven't looked hard), "sys.rzadmin.password" is only referenced from the login() function of /bin/httpd in the context of retrieving a value. This value is retrieved and compared before the error message "login err: password is wrong." is emitted. I can't find any other reference to code in any part of the firmware that may allow a user to change the default value of "sys.rzadmin.password".

Also for fun there is a function imsd_upload_log_v1 in /bin/imsd that collects SSIDs, MACs, IP addresses, sys.admin.username, sys.rzadmin.username, timezone, and another function imsd_remote_pwd_get in /bin/imsd that retrieves sys.admin.password. Related library /lib/lubucapi.so also looks like a fun binary to inspect more closely as it contains a command set that seemingly allows either cloud management of Tenda routers and/or remote debugging, and possibly is why imsd_remote_pwd_get exists in /bin/imsd

emsign• 15 days ago

Not to sound too alarming. But

Security holes in networking equipment

Affects not just the compromised devices.

like_any_other• 15 days ago

So will this finally be treated as sabotage/criminal hacking, or is it just yet another example of letting manufacturers do whatever they want to their customers without any punishment? Meanwhile if I find and publish the emails of Tenda customers that they accidentally left unprotected, I get raided by the FBI.

finalhacker• 15 days ago

Almost all consumer electronics come with backdoors—especially given the prevalence of computational advertising. Before criticizing Tenda, we ought to clarify whether this is a consumer-facing (2C) or business-facing (2B) product.

chirsz• 15 days ago

A quick search reveals several other serious vulnerabilities in Tenda routers that could grant administrator privileges. Therefore, I tend to believe this is due to the company's incompetence and lack of technical skill rather than malicious intent—but it's still a reason to avoid using Tenda products. There's a reason why Tenda's market share is far lower than TP-Link's.

Havoc• 15 days ago

The consistency with which networking hardware companies produce such garbage is crazy.

And it’s always amateur hour backdoors somehow. If it was something sophisticated they might get a pass on „ok some security agency made them do it probably“

KingOfCoders• 15 days ago

Or the amateur hour backdoors are those that are found.

Or the amateur hour backdoors are there to be found.

daneel_w4• 15 days ago

They didn't produce garbage by accident. They followed a plan and made a decision.

Ekaros• 15 days ago

Sad truth is that too few customers pay extra for proper security. And even then it is questionable will you get it.

pbasista2• 15 days ago

The associated username is not validated, so any provided username will succeed when paired with the backdoor password.

Great. I am really wondering why should the customers trust these manufacturers.

At this point I would not use any router with vendor-provided black box firmware. Full stop.

I would always install OpenWRT or something similar on it before using it.

And if that is not possible for whatever reason, I would not even think about buying such a device.

rootatixww33• 15 days ago

good approach, but your security should not depend on your router anyway, you should be immune to attacks from it

bayindirh2• 15 days ago

Not exposing your management interface to internet and running a guest network which doesn't have access to said management interfaces can block 95%+ of the attacks, I believe.

bayindirh2• 15 days ago

Last time when I looked OpenWRT was unable to support MIMO and beamforming capabilities of many of the devices it was running on.

This capabilities are crucial to have decent coverage, signal strength and throughput where I live (i.e.: crowded/congested wireless networks in an apartment complex).

Did OpenWRT team managed to work around them, or did the manufacturers started to play nicer with open drivers with loadable firmware?

486sx33• 15 days ago

Some routers specifically allow openWRT.. example, Routers like the GL.iNet GL-MT6000 (Flint 2) and TP-Link Archer AX6000 come with OpenWrt pre-installed and are designed for easy OpenWrt use.

pshirshov• 15 days ago

Hm, do you ever go over 1gbit? If my understanding is correct, good affordable routers like Mikrotik's CCR2004 are fully closed, so the only option is to build your own shitty box which will be much less energy efficient than their specialized switch chips.

dspillett• 15 days ago

Because of lax security in commercial routers, this backdoor being a prime example of what I'm concerned about, I'd have my own shitty box as a firewall between them and my other kit anyway, so there isn't an efficiency saving either way. It is just a choice of where the walls are, and therefor where my shitty box(es) is/are, not whether my shitty box exists or not.

Currently my primary shitty box router does everything wrt external connectivity and a bought AP/router sits inside offering WiFi. I'd like to remove that AP completely with a WiFi adaptor controlled by my shitty box, but I've not got around to that as it would mean learning to configure a mesh (and so at least one more of my own shitty boxes!) to get good coverage everywhere (I only have a small place, but there are still a couple of blind-ish spots depending on where I put the primary AP). Not trusting a bought router/AP to not have back doors like this raises the question: if they are going to add backdoors for direct outside connections, what is to stop the firmware instead/also trying to tunnel out and letting unwanted connections in that way? (other than this having less “plausible deniability” once discovered)

pbasista2• 15 days ago

do you ever go over 1gbit

No. None of the local ISPs offer speeds above 1 Gbps.

However, I use FriendlyElec NanoPi R5C as the main entrypoint router. It has two 2.5G ethernet ports. It costs less than 100 euros. And it runs OpenWRT.

It is not a multiport, multi-gigabit device though. And I have not tested it above 1 Gbps so I am unsure about its real world performance.

gh02t• 15 days ago

Pfsense or OPNsense can handle ~5 gbps routing/firewall on a low power AMD or Intel embedded chip. My now old Pfsense box I got off Aliexpress can comfortably handle 2.5 gbps on an ancient Celeron J4125 running around 10W total. 10+ gbps is feasible on a reasonable power budget with higher end hardware, though it starts to get more expensive.

linzhangrun• 15 days ago

Common situation for small-company software...

Backdoor passwords left for convenient debugging are not surprising anymore.

daneel_w4• 15 days ago

This is not a case of "convenient debugging".

deeddy• 15 days ago

I've seen it last night, and I was like wtf?! Frankly, if they tried to build in some backdoor, I bet they would have done it differently, not so obviously. This must have been some sort of stupidity done for testing purposes, and just got buried deep in the code and forgotten.

This is the main reason why you should always use OpenWRT or other opensource router OS. If it gets an issue, at least it would get patched in the next update.

high_byte• 15 days ago

this is definitely a backdoor, not necessarily that they use it to infiltrate users but definitely they put them at risk.

reminds me of a bug I found in some tplink router it compared passwords of 3 different users but that table was empty so basically 15 NULL bytes would log you in as admin lol

Fabricio20• 15 days ago

Oh this is amazing! I have a few of their cube routers sitting around and I always hated how app-locked their firmware was when it really is just a wifi repeater with a few extras (mesh) on top. Root access will do wonders to bypassing the app now (and also disabling their ping-for-green-light mechanism which spams the network with a constant dns resolution to microsoft.com lol).

Also honest take this looks less like a "backdoor" (implies malicious - this is a link to a CVE after all) and more like a developer access credential/default credential that was burned into the firmware (i'd imagine the code remains but on a production run they randomize the key so its non-guessable but then you get lazy and dont run that extra step and this slips in/you burn the bare firmware with no production configs).

tinyhitman• 15 days ago

why would a consumer device need a randomized password?

vajrabum• 15 days ago

Maybe so when you factory reset the device that it sets the admin to something you can maybe read off the label? At least that way the random attacker needs physical access to your space.

idiotsecant• 15 days ago

Yes, it is randomized but due to a quirk in the universal probability waveform it always randomizes to 'rzadmin'. Scientists are baffled.

mjmas• 15 days ago

Pulled out of fair hat. Guaranteed to be random.

zb3• 15 days ago

Typical for Chinese companies. Of course US companies also provide backdoors, but more official and more secure..

seethishat• 15 days ago

No backdoor is secure. Read the "Keys under Doormats" paper from 2015:

https://www.schneier.com/wp-content/uploads/2016/09/paper-ke...

daneel_w4• 15 days ago

What a surprise.

cedel2k1• 15 days ago

Reminds me of LKWPETER. I lost a bet when insinsting this couldn't be true.

megous• 15 days ago

Most of the software is this way, it seems. Military intelligenece in our country were recently changing configs on peoples routers without their knowledge or consent to get rid of similarly dangerous thing on several types of tp-link routers.

And if you ever looked inside the firmwares of these IoT Linux boxes (be it sip phones, payment terminals, ip cameras, routers, modems, etc.) you'd not want it anywhere near anything that needs to be secure. OpenWRT or your own thing, or very strict isolation, or nothing.

allankoech• 15 days ago

Was that admin password intended for internal testing but ended in prod?

"Unfortunately, we were unable to reach the vendor"

With the widespread adoption of Tenda products in my local area, someone can have a good time exploiting this vulnerability.

Tenda firmware (multiple versions) contains hidden authentication backdoor

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