Cisco warns it won't fix critical flaw in small business routers despite known exploit

Software support ended in 2021, so we’re relying on SMBs knowing how to block ports

Cisco "has not and will not release software updates" to address a critical flaw in four small business routers, despite having spotted proof of concept code for an exploit.

The networking giant on Wednesday advised that its model RV016, RV042, RV042G, and RV082 routers are subject to CVE-2023-20025 – a critical-rated authentication bypass vulnerability – as well as the medium-severity rated remote command execution vulnerability CVE-2023-20026.

CVE-2023-20025 could allow an unauthenticated remote attacker to bypass authentication on an affected device, thanks to improper validation of user input within incoming HTTP packets.

"An attacker could exploit this vulnerability by sending a crafted HTTP request to the web-based management interface. A successful exploit could allow the attacker to bypass authentication and gain root access on the underlying operating system," Cisco's warning states.

CVE-2023-20026 is also an HTTP validation problem, but can only be triggered when attackers possess valid administrative credentials for the affected device.

Cisco won't update the devices, for two reasons.

One is that disabling remote management and blocking access to ports 443 and 60443 is a workaround that prevents exploitation of the flaws.

The other is that the devices have reached end of life. Cisco ended support for the RV082 and RV016 in 2021, and software maintenance ended for the RV042 and RV042G in the same year – but the hardware will be supported until 2025.

Now for the tricky part: Cisco is "aware that proof-of-concept exploit code is available for the vulnerabilities that are described in this advisory" but "is not aware of any malicious use of the vulnerabilities that are described in this advisory."

But given that criminals routinely hunt for easy-to-attack platforms, it surely won't be long before someone attempts to exploit these vulnerabilities.

Security experts often tell The Register that small businesses are not renowned for their infosec capabilities or diligence. So while the fix is relatively trivial for a technical user, many actual owners of these machines will have no idea how to block access to ports 443 and 60443. That is, if they even receive news of the flaws.

Throw in the fact that small routers often just work for years at a time without intervention, and it is almost certain some of these devices are ripe for attack – and will be for the foreseeable future. ®

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