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2021-10 Security Bulletin: Junos OS: MX Series: Receipt of specific packet on MS-MPC/MS-MIC causes line card reset (CVE-2021-31351)



Article ID: JSA11216 SECURITY_ADVISORIES Last Updated: 14 Oct 2021Version: 2.0
Product Affected:
This issue affects specific versions of Junos OS (see below). Affected platforms: MX Series.

An Improper Check for Unusual or Exceptional Conditions in packet processing on the MS-MPC/MS-MIC utilized by Juniper Networks Junos OS allows a malicious attacker to send a specific packet, triggering the MS-MPC/MS-MIC to reset, causing a Denial of Service (DoS).

Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition.

This issue only affects specific versions of Juniper Networks Junos OS on MX Series:

  • 17.3R3-S11;
  • 17.4R2-S13;
  • 17.4R3 prior to 17.4R3-S5;
  • 18.1R3-S12;
  • 18.2R2-S8, 18.2R3-S7, 18.2R3-S8;
  • 18.3R3-S4;
  • 18.4R3-S7;
  • 19.1R3-S4, 19.1R3-S5;
  • 19.2R1-S6;
  • 19.3R3-S2;
  • 19.4R2-S4, 19.4R2-S5;
  • 19.4R3-S2;
  • 20.1R2-S1;
  • 20.2R2-S2, 20.2R2-S3, 20.2R3;
  • 20.3R2, 20.3R2-S1;
  • 20.4R1, 20.4R1-S1, 20.4R2;
  • 21.1R1;

This issue does not affect any version of Juniper Networks Junos OS prior to 15.1;

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was seen during production usage.

This issue has been assigned CVE-2021-31351.


The following software releases have been updated to resolve this specific issue: Junos OS 17.3R3-S12, 17.4R3-S5, 18.1R3-S13, 18.3R3-S5, 18.4R3-S8, 19.1R3-S6, 19.2R1-S7, 19.2R3-S2, 19.3R2-S6, 19.3R3-S3, 19.4R3-S3, 20.1R2-S2, 20.1R3, 20.2R3-S1, 20.3R3, 20.4R2-S1, 20.4R3, 21.1R1-S1, 21.1R2, 21.2R1, and all subsequent releases.

Note: Only those releases listed in the PROBLEM section above are affected. This fix has also been proactively committed into other releases that are not vulnerable to this issue.

This issue is being tracked as 1577814.

There are no viable workarounds for this issue.
Software releases or updates are available for download at
Modification History:
2021-10-13: Initial Publication.
2021-10-14: Typo in affected releases (20.2R3-S3 → 20.2R2-S3)

CVSS Score:
7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Severity Level:
Severity Assessment:
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."

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