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In recent years, several groups of cybersecurity researchers have disclosed dozens of memory side-channel vulnerabilities in modern processors and DRAMs, like RowhammerRAMBleedSpectre, and Meltdown.

Have you ever noticed they all had at least one thing in common?

That’s OpenSSH.

As a proof-of-concept, many researchers demonstrated their side-channel attacks against OpenSSH application installed on a targeted computer, where an unprivileged attacker-owned process exploits memory read vulnerabilities to steal secret SSH private keys from the restricted memory regions of the system.

That’s possible because OpenSSH has an agent that keeps a copy of your SSH key in the memory so that you don’t have to type your passphrase every time you want to connect to the same remote server.

However, modern operating systems by default store sensitive data, including encryption keys and passwords, in the kernel memory which can not be accessed by user-level privileged processes.

But since these SSH keys live on the RAM or CPU memory in plaintext format, the feature is susceptible to hacking attempts when the attacks involve memory read vulnerabilities.

images from Hacker News