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Sunday, 23 June 2019 08:17

OpenSSH adds protection against Spectre, Meltdown, Rowhammer and RAMBleed attacks Featured

OpenSSH adds protection against Spectre, Meltdown, Rowhammer and RAMBleed attacks Pixabay

The OpenSSH project has implemented changes in its implementation of secure shell to guard against speculative execution and memory side-channel attacks — Spectre, Meltdown, Rowhammer and RAMBleed — developer Damien Miller says.

In a mailing list post, Miller said the changes would add protection for private keys at rest in RAM.

OpenSSH is run by the OpenBSD project which is headed by Theo de Raadt. SSH or Secure Shell is a program used to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another. It provides strong authentication and secure communications over insecure channels. OpenSSH is a free implementation of the program.

Miller told iTWire in response to a query that the mitigation tried to make speculation and other leakage attacks unlikely to succeed. "The attacks all depend on having the data that they want to steal be available somewhere in RAM and exploit CPU or architectural weaknesses to get at some or all of it," he explained.

"The change we've made works by making the data that attackers would want to steal no longer directly available - they [private keys] are stored encrypted except for the moment they are needed. To decrypt them, we effectively scatter the key across a relatively large amount of memory, and require that the attacker read all of it exactly before they can recover the key and use it to decrypt the data they are trying to steal."

Spectre and Meltdown were disclosed in January 2018 and affect Intel processors made since 1995. Meltdown removes the barrier between user applications and sensitive parts of the operating system. Spectre, which is also reportedly found in some AMD and ARM processors, can trick vulnerable applications into leaking the contents of their memory.

According to Wikipedia, Rowhammer "is an unintended and undesirable side effect in dynamic random-access memory in which memory cells leak their charges and interact electrically between themselves, possibly leaking or changing the contents of nearby memory rows that were not addressed in the original memory access.

Rambleed takes advantage of the same flaw that is used for Rowhammer attacks, allowing an attacker to read the contents of protected memory, rather than modifying it.

Miller, who has been with the OpenSSH project since 1999 when it was started, said: "The attacks however are not perfect - they have a certain error rate when trying to steal copies of memory, and we expect that this error rate, coupled with the need for them to exactly recover the entire scattered key, will make the attacks impractical. If we're off in our math, then we still have a few improvements to make."

OpenSSH is the most widely used implementation of the secure shell protocol.

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Sam Varghese

Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.

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