Security New OpenSSH Vulnerability Could Lead to RCE as Root on Linux Systems

OpenSSH maintainers have released security updates to contain a critical security flaw that could result in unauthenticated remote code execution with root privileges in glibc-based Linux systems.

The vulnerability has been assigned the CVE identifier CVE-2024-6387. It resides in the OpenSSH server component, also known as sshd, which is designed to listen for connections from any of the client applications.

"The vulnerability, which is a signal handler race condition in OpenSSH's server (sshd), allows unauthenticated remote code execution (RCE) as root on glibc-based Linux systems," Bharat Jogi, senior director of the threat research unit at Qualys, said in a disclosure published today. "This race condition affects sshd in its default configuration."

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The cybersecurity firm said it identified no less than 14 million potentially vulnerable OpenSSH server instances exposed to the internet, adding it's a regression of an already patched 18-year-old flaw tracked as CVE-2006-5051, with the problem reinstated in October 2020 as part of OpenSSH version 8.5p1.

"Successful exploitation has been demonstrated on 32-bit Linux/glibc systems with [address space layout randomization]," OpenSSH said in an advisory. "Under lab conditions, the attack requires on average 6-8 hours of continuous connections up to the maximum the server will accept."

The vulnerability impacts versions between 8.5p1 and 9.7p1. Versions prior 4.4p1 are also vulnerable to the race condition bug unless they are patched for CVE-2006-5051 and CVE-2008-4109. It's worth noting that OpenBSD systems are unaffected as they include a security mechanism that blocks the flaw.

Specifically, Qualys found that if a client does not authenticate within 120 seconds (a setting defined by LoginGraceTime), then sshd's SIGALRM handler is called asynchronously in a manner that's not async-signal-safe.

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New OpenSSH Vulnerability Could Lead to RCE as Root on Linux Systems