Critical Vulnerability in OpenSSH – CVE-2024-6387

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What is regreSSHion (CVE-2024-6387)?

• Overview:
  • regreSSHion, CVE-2024-6387, is an unauthenticated remote code execution (RCE) vulnerability in OpenSSH’s server (sshd) on glibc-based Linux systems. Discovered by Qualys TRU, it grants full root access and affects the default configuration without requiring user interaction.
• Impact:
  • Full system takeover
  • Execution of arbitrary code with root privileges
  • Installation of malware and creation of backdoors
  • Potential data exfiltration and manipulation

regreSSHion Vulnerability Background

• Discovery:
  • Identified by the Qualys Threat Research Unit (TRU)
  • First significant OpenSSH vulnerability in nearly two decades
• Regression Explanation:
  • Reintroduction of a previously patched vulnerability (CVE-2006-5051)
  • Occurred due to changes in OpenSSH 8.5p1, released in October 2020

Affected Versions and Systems

• Vulnerable Versions:
  • OpenSSH versions earlier than 4.4p1, if not patched for CVE-2006-5051 and CVE-2008-4109
  • Versions 8.5p1 to 9.8p1
• Unaffected Versions:
  • Versions 4.4p1 to 8.4p1 (secured by transformative patch)
  • OpenBSD systems (secured by a 2001 security tweak)
• Scope:
  • 14 million potentially vulnerable OpenSSH instances identified via Censys and Shodan scans
  • Roughly 700,000 internet-facing instances at risk

Immediate Actions and Mitigations

• Patch Availability:
  • Patch for CVE-2024-6387
• Mitigation Steps:
  • Set LoginGraceTime to 0 in the configuration file to prevent exploitation (with caution)
  • Apply patches and reconfigure sshd
• Preventative Measures:
  • Regular updates and patch management
  • Thorough regression testing to avoid reintroduction of vulnerabilities

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