OpenSSH Vulnerability, No password required (CVE-2024-6387)

Mark Shine
July 7, 2024
min read

A critical new vulnerability has been discovered in OpenSSH's server (sshd), adding to a worrying trend of severe security issues identified in the past year. This is the third such vulnerability in the last 12 months, underscoring the urgent need for robust security practices and proactive measures in maintaining server integrity.

The recently discovered vulnerability in OpenSSH’s server (sshd) allows for unauthenticated remote code execution (RCE) as root. This type of vulnerability is especially dangerous because it enables attackers to gain the highest level of access on a target system without needing to authenticate. The vulnerability stems from a signal handler race condition, which can be exploited in sshd’s default configuration.

Affected Versions

  • OpenSSH 9.8p1 and earlier up to 8.5p1.
  • Before version 4.4p1

The identified versions include those widely used in many environments, making this vulnerability a significant threat to a vast number of systems.

Potential Impact

The potential impact of this vulnerability is severe. Here’s a closer look at what could happen if an attacker successfully exploits this issue:

  1. Full System Takeover: Unauthenticated RCE as root allows an attacker to gain complete control over the affected system. This means they can execute any command, modify any file, and change any setting on the system.
  2. Malware Installation: With root access, an attacker can install malicious software that can steal data, disrupt operations, or further compromise system security.
  3. Data Manipulation: Attackers can alter, delete, or corrupt data, which can lead to significant data loss or integrity issues.
  4. Creation of Backdoors: Attackers can create persistent backdoors that allow them to regain access even if their initial entry point is discovered and closed.
  5. Network Propagation: A compromised system can be used as a launching point to attack other systems within the same network, potentially leading to a broader compromise of the entire network.
  6. Bypassing Security Mechanisms: Root access allows attackers to disable or bypass critical security mechanisms such as firewalls, intrusion detection systems, and logging mechanisms, making it harder to detect and respond to their activities.
  7. Data Breaches: Attackers could access and exfiltrate sensitive or proprietary information, leading to data breaches that can have severe financial and reputational impacts.

Mitigation Steps

To protect your systems from this critical vulnerability, immediate action is necessary. Here are the steps you should take:

  • Update OpenSSH: Ensure you are using the latest version of OpenSSH. The developers have already released a patch for this issue, so updating your software will protect you from this specific vulnerability.
  • Configure sshd for Enhanced Security:
    • Set UsePrivilegeSeparation: This configuration option isolates privileges, meaning that even if an attacker exploits a vulnerability, they will be restricted in what they can do. To enable this, add the following line to your sshd_config file:

UsePrivilegeSeparation sandbox

  • Enable UsePAM: Pluggable Authentication Modules (PAM) provide a framework for integrating multiple low-level authentication schemes into a high-level API. Enabling PAM adds an extra layer of security. To enable this, add the following line to your sshd_config file:
UsePAM yes
  • Monitor Auth Logs and Set Up Alerts: Regularly monitor the authentication logs (/var/log/auth.log on many Linux systems) for any suspicious activity. Set up alerts to notify you of unusual login attempts or patterns that could indicate an attack. For example, you can use tools like logwatch, fail2ban, or configure custom scripts to send alerts:
    • Install logwatch:
sudo apt-get install logwatch

  • Configure logwatch to monitor /var/log/auth.log and send daily reports:
sudo nano /etc/cron.daily/00logwatch
  • Add the following line:
/usr/sbin/logwatch --output mail --mailto --detail high

Frequency of Similar Incidents

It’s important to note that this type of critical vulnerability has been identified three times in the past 12 months. This recurring pattern highlights the ongoing need for vigilance and proactive security measures. The fast-paced nature of technology development means that new vulnerabilities are constantly emerging, and staying ahead of these threats requires continuous effort and attention.

Reproducing the Vulnerability

For educational purposes and to understand the exploit, here's a simplified example of how an attacker might reproduce the vulnerability:

  1. Identify the Target System: The attacker scans the network to identify systems running vulnerable versions of OpenSSH.
  2. Craft the Exploit: The attacker crafts a specific exploit to take advantage of the signal handler race condition.
  3. Execute the Exploit: The attacker sends the exploit payload to the target system. Due to the nature of race conditions, multiple attempts may be required for successful exploitation.
  4. Gain Access: Once the exploit succeeds, the attacker gains unauthenticated remote code execution as root on the target system.

Note: Exploiting vulnerabilities is illegal and unethical unless done in a controlled and authorized environment for testing and improving security measures.

Why Not Double Down to Protect Against These Attacks?

In addition to the immediate steps to mitigate this specific vulnerability, consider implementing broader security practices to protect your systems against future threats:

  • Implement Multi-Factor Authentication (MFA): Adding an extra layer of authentication can help prevent unauthorized access, even if an attacker gains access to login credentials.
  • Use Strong, Unique Passwords: Ensure that all accounts use strong, unique passwords that are regularly updated. Consider using a password manager to help manage and generate secure passwords.
  • Limit Access: Follow the principle of least privilege, ensuring that users and applications have only the permissions they need to perform their tasks.
  • Monitor and Respond: Implement robust monitoring and response strategies to detect and address potential security incidents quickly. This includes setting up alerts for suspicious activity and having a response plan in place.
  • Backup and Recovery: Regularly backup your data and ensure you have a tested recovery plan in place. In the event of a compromise, being able to quickly restore your systems and data can significantly reduce downtime and impact.

Stay Vigilant

The discovery of this new OpenSSH vulnerability serves as a reminder of the ever-present threat landscape we face. By staying vigilant, keeping your systems up to date, and following best security practices, you can protect your organization from this and other security threats.

By taking these steps, you can safeguard your systems against the critical vulnerabilities that pose a significant threat to your organization's security. If you need assistance or have any questions, don’t hesitate to get in touch with Ankra. Together, we can ensure that systems remain secure and resilient against emerging threats.

Share this post


Joining your building of your app with CICD and deploying it with IaC, lets dive in.
Mark Shine
June 4, 2024
min read
scaling applications transforms from a daunting task into a symphony of efficiency and innovation.
Mark Shine
June 4, 2024
min read
Limitations of Infrastructure as code, its bigger then that.
Mattias Åsell
June 4, 2024
min read