CVE-2021-31360 : What You Need to Know

An improper privilege management vulnerability in the Juniper Networks Junos OS and Junos OS Evolved command-line interpreter (CLI) allows a low-privileged user to overwrite local files as root, possibly leading to a system integrity issue or Denial of Service (DoS). This vulnerability affects Juniper Networks Junos OS versions prior to 15.1R7-S10, 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.2R1-S7, 19.2R3-S3, 19.3R2-S6, 19.3R3-S3, 19.4R3-S6, 20.1R2-S2, 20.1R3-S1, 20.2R3-S2, 20.3R3, 20.4R2-S1, 20.4R3, and 21.1R1-S1, 21.1R2, as well as Junos OS Evolved versions prior to 20.4R2-S3-EVO and all versions of 21.1-EVO.

Understanding CVE-2021-20657

This vulnerability in Junos OS and Junos OS Evolved allows a low-privileged user to manipulate files as root, potentially leading to system integrity issues or Denial of Service.

What is CVE-2021-20657?

CVE-2021-20657 is an improper privilege management vulnerability in Juniper Networks Junos OS and Junos OS Evolved that enables a low-privileged user to overwrite local files as root, potentially resulting in a system integrity problem or Denial of Service.

The Impact of CVE-2021-20657

Exploitation of this vulnerability could lead to a sustained Denial of Service (DoS) condition, requiring manual intervention to recover. Systems are only vulnerable if the jdhcpd process is running.

Technical Details of CVE-2021-20657

This vulnerability has a CVSSv3.1 base score of 7.1, with a high impact on integrity and availability. The attack complexity is low, requiring low privileges.

Vulnerability Description

The vulnerability allows a low-privileged user to overwrite local files as root, potentially causing system integrity issues or DoS.

Affected Systems and Versions

Juniper Networks Junos OS versions prior to 15.1R7-S10, 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.2R1-S7, 19.2R3-S3, 19.3R2-S6, 19.3R3-S3, 19.4R3-S6, 20.1R2-S2, 20.1R3-S1, 20.2R3-S2, 20.3R3, 20.4R2-S1, 20.4R3, 21.1R1-S1, 21.1R2 are affected. Junos OS Evolved versions prior to 20.4R2-S3-EVO and 21.1-EVO are also vulnerable.

Exploitation Mechanism

The vulnerability allows a low-privileged user to overwrite critical files as root, potentially leading to DoS or system integrity issues.

Mitigation and Prevention

To address CVE-2021-20657, Juniper Networks has provided software updates that resolve this specific issue.

Immediate Steps to Take

Update the affected software to the patched versions mentioned by Juniper Networks.

Long-Term Security Practices

Implement access lists or firewall filters to restrict CLI access to the device from trusted hosts and administrators.

Patching and Updates

Apply the software updates provided by Juniper Networks to mitigate the vulnerability and enhance system security.