CVE-2024-21591: Critical Remote Code Execution Vulnerability in Juniper Networks Junos OS

Vulnerability Summary

• CVE ID: CVE-2024-21591​

• Severity: Critical (CVSS 3.1 Score: 9.8)

• Attack Vector: Network​

• Privileges Required: None​

• User Interaction: None​

• Impact: Remote Code Execution (RCE), Denial of Service (DoS), Root Privilege Escalation​

CVE-2024-21591 is a critical out-of-bounds write vulnerability in the J-Web interface of Juniper Networks’ Junos OS, affecting SRX Series firewalls and EX Series switches. The flaw arises from the use of an insecure function that allows attackers to overwrite arbitrary memory, potentially leading to remote code execution or denial of service. ​

Affected Products

The vulnerability impacts the following versions of Junos OS:​

• Versions earlier than 20.4R3-S9​

• 21.2 versions earlier than 21.2R3-S7​

• 21.3 versions earlier than 21.3R3-S5​

• 21.4 versions earlier than 21.4R3-S5​

• 22.1 versions earlier than 22.1R3-S4​

• 22.2 versions earlier than 22.2R3-S3​

• 22.3 versions earlier than 22.3R3-S2​

• 22.4 versions earlier than 22.4R2-S2 and 22.4R3​

Devices with the J-Web interface enabled are particularly at risk. ​

Exploitation Details

The vulnerability stems from an insecure function that allows attackers to overwrite arbitrary memory. Exploitation can lead to remote code execution or denial of service. An exploit has been developed, demonstrating the ease with which this vulnerability can be leveraged.

Mitigation Recommendations

• Apply Patches: Juniper Networks has released patches addressing this vulnerability. Affected versions should be updated to the following or later:​

  • 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​

• Disable J-Web Interface: If immediate patching is not feasible, disable the J-Web interface to mitigate exposure.

• Restrict Access: Limit access to the J-Web interface to trusted hosts only, reducing the attack surface.

Conclusion

CVE-2024-21591 represents a significant security risk to organizations utilizing Juniper Networks’ SRX Series firewalls and EX Series switches with vulnerable versions of Junos OS. Given the critical nature of the vulnerability and the availability of an exploit, immediate action is required to patch affected systems and implement recommended mitigations.​

References

• NVD – CVE-2024-21591​

• Juniper Security Advisory

• Curesec Analysis​

• Censys Report​

• Qualys Threat Protection​