CVE-2021-31351 Explained : Impact and Mitigation

An in-depth look at CVE-2021-31351, a vulnerability in Juniper Networks Junos OS affecting MX Series that could lead to a Denial of Service (DoS) attack.

Understanding CVE-2021-20657

This section provides detailed insights into the nature and impact of CVE-2021-31351.

What is CVE-2021-31351?

CVE-2021-31351 involves an Improper Check for Unusual or Exceptional Conditions in packet processing on the MS-MPC/MS-MIC devices used by Juniper Networks Junos OS. This flaw enables a malicious actor to send a specific packet, forcing the MS-MPC/MS-MIC to reset, ultimately resulting in a Denial of Service (DoS) attack. The continued receipt and processing of this packet exacerbate the DoS condition. This vulnerability specifically affects certain versions of Junos OS on MX Series devices.

The Impact of CVE-2021-31351

The CVSS v3.1 base score for CVE-2021-31351 is 7.5, marking it as a high severity issue. The attack complexity is low, and the attack vector is via network. The vulnerability's exploitation could result in a sustained Denial of Service (DoS) condition, with a high impact on availability.

Technical Details of CVE-2021-31351

This section delves into the specifics of the vulnerability, including affected systems, versions, and exploitation mechanisms.

Vulnerability Description

The vulnerability arises from an improper check for exceptional conditions in packet processing on MS-MPC/MS-MIC devices utilized by Juniper Networks Junos OS.

Affected Systems and Versions

Specific versions of Juniper Networks Junos OS on MX Series are impacted by this vulnerability, including 17.3R3-S11, 17.4R2-S13, 17.4R3 up to 17.4R3-S5, and several others listed in the description section.

Exploitation Mechanism

As of the latest update, there have been no reported cases of malicious exploitation of this vulnerability according to Juniper SIRT.

Mitigation and Prevention

Learn about the immediate steps to take and the long-term security practices to mitigate the risks associated with CVE-2021-31351.

Immediate Steps to Take

Since there are no viable workarounds for this issue, it is crucial to patch affected systems promptly to prevent potential DoS attacks.

Long-Term Security Practices

Implement robust network security measures, follow vendor advisories, and stay updated on security patches to minimize the risk of exploitation.

Patching and Updates

Juniper Networks has released updated software versions to address CVE-2021-31351. Ensure your systems are running the patched versions: Junos OS 17.3R3-S12, 17.4R3-S5, 18.1R3-S13, and subsequent releases not listed as affected.