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Cybersecurity Threat Advisory

A critical pre-authentication remote code execution (RCE) vulnerability, CVE-2024-21591, has been patched in Juniper Networks’ Junos OS on SRX firewalls and EX switches. Exploitable via an out-of-bounds write, the flaw poses risks of denial-of-service (DoS), RCE attacks, or unauthorized root access. Barracuda MSP advises organizations to immediately patch affected versions, create network segmentation, and continuously monitor the network for potential exploitation. Continue reading this Cybersecurity Threat Advisory to learn more about the impact of this critical vulnerability.

What is the threat?

The threat encompasses a critical out-of-bounds write vulnerability affecting Juniper Networks’ Junos OS on SRX firewalls and EX switches. Exploiting this flaw involves leveraging the insecure function to overwrite arbitrary memory and providing attackers with unauthorized access without the need for authentication that can result in unauthenticated, network-based threat actors triggering a DDoS attack, executing RCE, or potentially gaining root privileges on exposed devices.

The affected versions are as follow:

  • Junos OS versions earlier than 20.4R3-S9
  • Junos OS 21.2 versions earlier than 21.2R3-S7
  • Junos OS 21.3 versions earlier than 21.3R3-S5
  • Junos OS 21.4 versions earlier than 21.4R3-S5
  • Junos OS 22.1 versions earlier than 22.1R3-S4
  • Junos OS 22.2 versions earlier than 22.2R3-S3
  • Junos OS 22.3 versions earlier than 22.3R3-S2
  • Junos OS 22.4 versions earlier than 22.4R2-S2, 22.4R3

Why is it noteworthy?

Juniper Networks’ Junos OS, SRX firewalls, and EX switches are used by organizations of all sizes. The exploitation of this vulnerability could lead to severe consequences, including unauthorized access, data breaches, and service disruptions. Given the historical targeting of Juniper networking devices by threat actors, this vulnerability introduces a substantial risk, emphasizing the urgency for organizations to address and mitigate the issue promptly. The potential for chaining vulnerabilities, as observed in previous instances, further underscores the need for vigilance and swift action.

What is the exposure or risk?

The exposure and risk associated with CVE-2024-21591 is substantial, posing a threat to systems relying on Juniper Networks’ Junos OS, specifically SRX firewalls and EX switches. The exploitation of this vulnerability could lead to the compromise of critical systems, unauthorized access to sensitive information, and disruption of essential services. Organizations utilizing Juniper networking devices, especially those with exposed J-Web interfaces, are at heightened risk. The potential for further compromise is notable. Swift mitigation is crucial to prevent data breaches, service disruptions, and unauthorized access.

What are the recommendations?

Barracuda MSP recommends the following actions to limit the impact of an attack against your network:

  • Immediate Patching: Organizations should promptly apply the patches provided by Juniper Networks for the affected Junos OS versions (20.4R3-S9, 21.2R3-S7, 21.3R3-S5, 21.4R3-S5, 22.1R3-S4, 22.2R3-S3, 22.3R3-S2, 22.4R2-S2, 22.4R3, 23.2R1-S1, 23.2R2, 23.4R1, and subsequent releases).
  • Network Segmentation: Implement network segmentation to limit the potential impact of successful attacks, isolating critical systems from compromised ones.
  • Monitoring and Detection: Enhance monitoring capabilities to detect any suspicious activity or unauthorized access, enabling a rapid response to potential threats.
  • Security Policies: Review and update security policies to align with the latest threat landscape, emphasizing the importance of timely patching and proactive security measures.
  • Communication and Awareness: Inform relevant stakeholders about the vulnerability, the applied patches, and encourage collaboration to strengthen overall cybersecurity posture. Additionally, consider disabling the J-Web interface or limiting access to trusted hosts as interim measures for those unable to apply patches immediately.


For more in-depth information about the recommendations, please visit the following links:

If you have any questions about this Cybersecurity Threat Advisory, please contact Barracuda XDR’s Security Operations Center.

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Anika Jishan

Posted by Anika Jishan

Anika is a Cybersecurity Analyst at Barracuda MSP. She's a security expert, working on our Blue Team within our Security Operations Center. Anika supports our XDR service delivery and is highly skilled at analyzing security events to detect cyber threats, helping keep our partners and their customers protected.

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