Security vendor DefenseCode disclosed the flaw last week, saying that it could be in multiple Linksys models. On Thursday, Cisco said the vulnerability was only in the Linksys WRT54GL.
"At this point, no other Linksys products appear to be impacted," Cisco said in a statement. "We have developed and are testing a fix for this issue, and will release it for our customers as soon as possible."
Until a patch is available, Cisco recommended that customers make sure their network is securely configured and that strangers or people who cannot be trusted do not use an Ethernet cable to connect to the router.
Neither Cisco nor DefenseCode has provided details of the vulnerability. After being told of Cisco's statement, DefenseCode did a "quick analysis" and found that "at least one other Linksys model is probably vulnerable," Chief Executive Leon Juranic said in an email. In addition, the company has told Cisco about "a few other potential vulnerabilities in the Linksys equipment."
DenfenseCode was also checking to see whether network devices from other manufacturers contained the same flaw.
Earlier this week, DefenseCode said in a blog post that the vulnerability was in the default installation of Linksys routers. The company posted a YouTube video showing a proof-of-concept exploit being used to gain root access to a Linksys WRT54GL running the latest version of firmware, 4.30.14.
A few "shady" third parties offered to buy the exploit, which DenfenseCode refused to do, Juranic said. "We don't sell exploits."
In December, Cisco hired Barclays to find a buyer for Linksys, Bloomberg reported. The network equipment maker is looking to sell the unit as part of its strategy to get rid of its consumer businesses in order to focus on corporate products.