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2021-07 Security Bulletin: Junos OS and Junos OS Evolved: RPD could crash in SR-ISIS/MPLS environment due to a flap of a ISIS link in the network (CVE-2021-0287)



Article ID: JSA11189 SECURITY_ADVISORIES Last Updated: 14 Jul 2021Version: 1.0
Product Affected:
This issue affects Junos OS 19.4, 20.1, 20.2, 20.3. This issue affects Junos OS Evolved 19.4, 20.1, 20.2, 20.3, 20.4.

In an Segment Routing ISIS (SR-ISIS)/MPLS environment, on Juniper Networks Junos OS and Junos OS Evolved devices, configured with ISIS Flexible Algorithm for Segment Routing and sensor-based statistics, a flap of a ISIS link in the network, can lead to a routing process daemon (RPD) crash and restart, causing a Denial of Service (DoS). Continued link flaps will create a sustained Denial of Service (DoS) condition.

This issue affects:

Juniper Networks Junos OS:

  • 19.4 versions prior to 19.4R1-S4, 19.4R3-S2;
  • 20.1 versions prior to 20.1R2-S1, 20.1R3;
  • 20.2 versions prior to 20.2R2-S2, 20.2R3;
  • 20.3 versions prior to 20.3R2;

Juniper Networks Junos OS Evolved:

  • 20.3-EVO versions prior to 20.3R2-EVO;
  • 20.4-EVO versions prior to 20.4R2-EVO.

This issue does not affect:

Juniper Networks Junos OS releases prior to 19.4R1.

Juniper Networks Junos OS Evolved releases prior to 19.4R1-EVO.

The two config stanzas required to be affected by this issue are shown below:

[ routing-options flex-algorithm <name> ]

[ protocols isis source-packet-routing sensor-based-stats per-sid egress ]

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-2021-0287.


The following software releases have been updated to resolve this specific issue:

Junos OS: 19.4R1-S4, 19.4R3-S2, 20.1R2-S1, 20.1R3, 20.2R2-S2, 20.2R3, 20.3R2, 20.4R1, and all subsequent releases.

Junos OS Evolved: 20.3R2-EVO, 20.4R2-EVO, 21.1R1-EVO, and all subsequent releases.

This issue is being tracked as 1555627.


Configuration of IS-IS Flexible Algorithm for Segment Routing or sensor-based statistics can be disabled to mitigate this issue.

Software releases or updates are available for download at
Modification History:
2021-07-14: Initial Publication.

CVSS Score:
6.5 (CVSS:3.1/AV:A/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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