SSH Protects the World’s Most Sensitive Networks. It Just Got a Lot Weaker

upstart writes:

Novel Terrapin attack uses prefix truncation to downgrade the security of SSH channels:

Sometime around the start of 1995, an unknown person planted a password sniffer on the network backbone of Finland's Helsinki University of Technology (now known as Aalto University). Once in place, this piece of dedicated hardware surreptitiously inhaled thousands of user names and passwords before it was finally discovered. Some of the credentials belonged to employees of a company run by Tatu Ylonen, who was also a database researcher at the university.

The event proved to be seminal, not just for Ylonen's company but for the entire world. Until that point, people like Ylonen connected to networks using tools which implemented protocols such as Telnet, rlogin, rcp, and rsh. All of these transmitted passwords (and all other data) as plaintext, providing an endless stream of valuable information to sniffers. Ylonen, who at the time knew little about implementing strong cryptography in code, set out to develop the Secure Shell Protocol (SSH) in early 1995, about three months after the discovery of the password sniffer.

[...] Ylonen submitted SSH to the Internet Engineering Taskforce in 1996, and it quickly became an almost ubiquitous tool for remotely connecting computers. Today, it's hard to overstate the importance of the protocol, which underpins the security of apps used inside millions of organizations, including cloud environments crucial to Google, Amazon, Facebook, and other large companies.

[...] Now, nearly 30 years later, researchers have devised an attack with the potential to undermine, if not cripple, cryptographic SSH protections that the networking world takes for granted.

Named Terrapin, the new hack works only when an attacker has an active adversary-in-the middle position on the connection between the admins and the network they remotely connect to. Also known as a man-in-the-middle or MitM attack, this occurs when an attacker secretly positioned between two parties intercepts communications and assumes the identity of both the recipient and the sender. This provides the ability to both intercept and to alter communications. While this position can be difficult for an attacker to achieve, it's one of the scenarios from which SSH was thought to have immunity.

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