Netgear patch said to leave backdoor problem in router

A security researcher claims Netgear's firmware update further hides the backdoor, but doesn't remove it

The security researcher who identified an admin backdoor in a range of routers last year has found that Netgear's patches don't adequately address the security issue.

In December, Eloi Vanderbeken discovered that he could get a remote root shell on his Linksys WAG200G router without authenticating when connecting to the device over TCP port 32764. The same backdoor feature was later confirmed in 24 router models sold under the Netgear, Cisco Systems, Linksys (now owned by Belkin) and Diamond brands and it was believed to have its origins in firmware code developed by Sercomm, a Taiwan-based manufacturer of wireless and broadband equipment that serves as hardware partner for multiple networking vendors.

Vanderbeken, a researcher at Paris-based IT security firm Synacktiv, recently downloaded and analyzed a firmware update released by Netgear for its DGN1000 Wireless router and DSL modem that was supposed to have fixed the issue. He found that the backdoor is no longer directly accessible over port 32764 TCP, but that it can be reactivated by sending raw Ethernet packets to the device with protocol type 0x8888 and the MD5 signature of the router model (DGN1000) as the payload.

"The 0x8888 ethertype and packet structure is used in an old Sercomm update tool," the researcher said in a report of his findings.

Once the device receives such a packet, the backdoor is reactivated and starts listening on port 32764 again, Vanderbeken said Tuesday via email.

The vulnerability is now harder to exploit because an attacker can only send the required raw packets from the same local area network as the targeted device or from one hop away, like its ISP. However, the backdoor is essentially still there, according to the researcher.

This mechanism involving specifically crafted raw Ethernet packets does not exist in the older firmware, he said. "It was added on purpose, to reactivate the backdoor. This is 100 percent intentional."

In addition to giving attackers the ability to execute commands with root access -- the highest privilege on Linux systems -- the backdoor also allows flashing the router LEDs by sending special messages to the device.

"I don't know if it was Netgear, Sercomm or both who decided to keep the backdoor open but it is deliberate," the researcher said. "I don't know why. There is no legitimate reason to do so."

There is a physical button that can be used to reset the router to factory defaults if needed in technical support cases and the setup wizard doesn't require the backdoor for remote configuration either, Vanderbeken said. "It's used internally by some services to update the configuration but it is never used from outside the router. There is no reason to keep it open."

The vulnerability was properly patched in at least one device that had previously been identified as affected -- the Cisco WAP4410N wireless access point. A firmware update for that device causes the backdoor to listen only to the loopback address 127.0.0.1, meaning it can't be accessed remotely, according to the researcher.

The new mechanism for reactivating the backdoor might be present in other previously affected routers that received firmware patches for the vulnerability, but so far the researcher has only tested the update for the Netgear DGN1000.

"Sercomm is the manufacturer of the routers found vulnerable to the port 32764 backdoor," the researcher said. "It's almost certain that they introduced the backdoor and the new service to reactivate it."

Netgear is in the process of issuing firmware updates for products that contained the backdoor: DG834G, DG384B, DGN3500B, DGN2000B, DGND330Bv2, DM111Pv2, DM111PSPv2, JNR3210, DGN3500, DGN1000 v1, DGN1000 v2 and DGN1000B. Updates had already been released for the last four models.

"All but two -- DM111PSPv2 and JNR3210 -- of these products are no longer being manufactured," the company said in an emailed statement.

"We are currently working with our technology partner, Sercomm, to investigate the assertions that the firmware patch did not remove the vulnerability," the company said. "If we find that any issues exist, we will make the necessary firmware changes and update the installed base."

Sercomm did not immediately respond to a request for comment.

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.

Tags privacyNetworkingspywareLinksysnetgearintrusionnetworking hardwarebelkinCisco SystemspatchesAccess control and authenticationExploits / vulnerabilitiesSynacktiv

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Brand Post

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Luke Hill

MSI GT75 TITAN

I need power and lots of it. As a Front End Web developer anything less just won’t cut it which is why the MSI GT75 is an outstanding laptop for me. It’s a sleek and futuristic looking, high quality, beast that has a touch of sci-fi flare about it.

Emily Tyson

MSI GE63 Raider

If you’re looking to invest in your next work horse laptop for work or home use, you can’t go wrong with the MSI GE63.

Laura Johnston

MSI GS65 Stealth Thin

If you can afford the price tag, it is well worth the money. It out performs any other laptop I have tried for gaming, and the transportable design and incredible display also make it ideal for work.

Andrew Teoh

Brother MFC-L9570CDW Multifunction Printer

Touch screen visibility and operation was great and easy to navigate. Each menu and sub-menu was in an understandable order and category

Louise Coady

Brother MFC-L9570CDW Multifunction Printer

The printer was convenient, produced clear and vibrant images and was very easy to use

Edwina Hargreaves

WD My Cloud Home

I would recommend this device for families and small businesses who want one safe place to store all their important digital content and a way to easily share it with friends, family, business partners, or customers.

Featured Content

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?