The older WNDR3700v3 hardware revision does not appear to be affected, Cutlip said, adding that he hasn't analyzed the firmware for the much older v1 and v2 revisions yet.
The researcher also discovered a separate authentication bypass vulnerability in the WNDR3700v4 firmware that's not related to the BRS_* issue. "Appending the string 'unauth.cgi' to HTTP requests will bypass authentication for many, if not most, pages," he said.
Cutlip didn't test if WNDR4700 is also vulnerable to this second flaw.
Netgear did not immediately respond to a request for comment.
A search for WNDR3700v4 routers that have their Web interface exposed to the Internet returned over 600 devices on the SHODAN search engine.
"Do not turn on remote administration ever, for any device," Cutlip said. "That's the number one attack surface and it's the one we usually find bugs in."
To avoid local attacks administrators should secure their wireless networks with strong WPA2 passphrases and make sure strangers are not allowed on their local networks, the researcher said.
These vulnerabilities are unlikely to go away soon, even if patches do get released, because many users never update their routers and other embedded systems. That's because they don't know how or because they're not aware of the risks, and a lack of clear communication about security issues from many vendors contributes to this problem.
Back in April, Craig Young, a security researcher at security firm Tripwire, found critical vulnerabilities in the Web management interface of Netgear's ReadyNAS network-attached storage products, including a vulnerability that could be exploited through a single unauthenticated HTTP request to gain complete root access to ReadyNAS devices.
He privately reported the issues to Netgear and the company released RAIDiator firmware versions 4.2.24 and 4.1.12 in July to address them. However, the majority of ReadyNAS devices exposed to the Internet are still vulnerable, according to Young.
"Shodan seems to indicate that there are more than 10,000 public IP addresses that match my ReadyNAS fingerprint," Young said Monday in a blog post. "Based on a sample size of 2,000 hosts, approximately 73 percent of the Internet exposed ReadyNAS are running RAIDiator firmware prior to 4.2.24."
"The impact of this ReadyNAS bug is enormous because it doesn't require authentication and attackers gain easy access to incoming user credentials. Successful attackers also gain access to all data stored on the NAS and can use it as a platform for attacks against other network systems," the researcher said in an emailed statement.
Young believes that Netgear is partially responsible for users not being aware of the risks associated with the vulnerabilities he found.
"The only mention of security concerns were in the firmware release notes," he said. "There's just one line: 'Updated Frontview to fix security issues.' Without knowledge of the specific vulnerabilities, customers feel no sense of urgency about installing the update."