Knock, knock. Who's there? NAT. Nat who? A NAT URL-borne killer
Last year's slipstream technique revived to pierce vulnerable firewalls – browsers patched to thwart bypass attempts
Video Ben Seri and Gregory Vishnepolsky, threat researchers at Armis, have found a way to expand upon the NAT Slipstream attack disclosed last year by Samy Kamkar, CSO of Openpath Security.
NAT Slipstream v2 takes the technique further by allowing a hacker to penetrate a vulnerable NAT/firewall and reach any internal IP on the network, rather than just the IP address of the victim's device.
In other words, it may expose every connected thing on a targeted network – printers, video cameras, industrial control systems, and other unmanaged hardware – to the internet. Such devices, which generally lack security controls, may then be compromised and commandeered or otherwise abused.
When Kamkar corresponded with The Register last year, he noted that browsers support protocols like WebRTC TURN (Traversal Using Relays around NAT) that evade port blocks and might be useful for further attacks.
You were warned
NAT Slipstream v2 validates that supposition. It relies on H.323, a VoIP protocol similar to SIP, and WebRTC TURN.
The process is demonstrated in this video:
But Seri and Vishnepolsky add that the risk presented by this attack depends upon how the traffic gets handled and the specific implementation of the targeted system because not all NATs provide ALGs nor enable them by default.
On Linux 4.14 and above, they observe, the exploited ALG behavior is disabled by default for security reasons. At the same time, they point out that consumer-grade routers rely on older Linux versions and some Linux-based products re-activate the vulnerable behavior. They said that OpenWRT, a Linux based router distribution using the 4.1 kernel, is not affected, but "most routers/NATs/firewalls are affected at least in some way."
The researchers disclosed their findings to the major browser vendors back in November 2020, and patches, consisting of port restrictions, have been deployed since then.
Chrome's fix arrived in v87.0.4280.141, on January 6, 2021. Microsoft Edge also deployed its fix, in v87.0.664.75, Apple released Safari v14.0.3 beta, with a stable channel release expected soon. And Mozilla's fixed up Firefox 85 arrived on Tuesday, January 26.
Seri and Vishnepolsky expressed doubt that these defenses will be the end of this particular attack vector. NATs, they say, were designed at a time when security was not a priority.
"Legacy requirements such as ALGs, are still a dominant theme in the design of NATs, today, and are the primary reason bypassing attacks are found again and again," they conclude. ®
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