Severe OpenSSH Flaw ‘regreSSHion’ Puts Millions of Linux Systems at Risk

A recently discovered critical vulnerability known as ‘regreSSHion’ puts millions of Linux systems at severe risk. Identified as CVE-2024-6387, this flaw affects the OpenSSH server (sshd) on glibc-based Linux systems, allowing unauthenticated attackers to gain root access and potentially take complete control of the affected machines.

CVE-2024-6387, Also Known as regreSSHion

The vulnerability, a signal handler race condition in OpenSSH’s server (sshd), impacts sshd in its default configuration and requires no user interaction. This race condition enables unauthenticated remote code execution (RCE) as root, giving attackers full control over the affected systems. This flaw exists in OpenSSH versions from 8.5p1 up to, but not including, 9.8p1, reintroducing a previously patched issue from CVE-2006-5051.

Security researchers noted, “This bug marks the first OpenSSH vulnerability in nearly two decades—an unauthenticated RCE that grants full root access. It affects the default configuration and does not require user interaction, posing a significant exploit risk.”

The scope of the vulnerability is extensive, with Censys and Shodan searches identifying over 14 million potentially vulnerable OpenSSH server instances. Data reveals that approximately 700,000 of these are exposed to the Internet, representing a significant portion of the global customer base.

Successful exploitation of regreSSHion could lead to complete system compromise, enabling attackers to install malware, manipulate data, and establish backdoors for persistent access. The ability to propagate through networks and bypass security mechanisms makes this vulnerability particularly dangerous for enterprises and individuals alike.

Exploitation Challenges and Future Risks

Although exploiting this vulnerability is challenging due to its remote race condition nature, requiring multiple attempts for a successful attack, advancements in deep learning could significantly increase exploitation rates. These technologies may provide attackers with sophisticated methods to leverage such security flaws, making timely mitigation crucial.

Mitigation Recommendations

To address the regreSSHion vulnerability, enterprises should adopt a focused and layered security approach:

  • Patch Management: Promptly apply available patches for OpenSSH and prioritize regular update processes to ensure all systems are protected.
  • Enhanced Access Control: Limit SSH access through network-based controls to minimize attack risks.
  • Network Segmentation and Intrusion Detection: Implement network segmentation to restrict unauthorized access and lateral movements within critical environments. Deploy intrusion detection systems to monitor and alert on unusual activities indicative of exploitation attempts.

By implementing these measures, organizations can significantly reduce the risk posed by this critical vulnerability and protect their systems from potential exploitation.


The discovery of CVE-2024-6387 underscores the importance of diligent cybersecurity practices and the necessity of safeguarding and continuously monitoring systems. Organizations must act promptly to patch vulnerable systems and strengthen their security posture to mitigate the risks associated with this severe vulnerability.


  1. Regularly update and patch all systems to address known vulnerabilities.
  2. Implement strong access controls and limit SSH access to essential personnel only.
  3. Utilize network segmentation and intrusion detection systems to swiftly respond to suspicious activities.
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