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CVE-2021-31363

Junos OS and Junos OS Evolved: Receipt of a specific LDP message will cause a Denial of Service

Medium6.5EPSS 0.40%
Published
Updated
Reserved
Assigned by
juniper

Description

In an MPLS P2MP environment a Loop with Unreachable Exit Condition vulnerability in the routing protocol daemon (RPD) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated adjacent attacker to cause high load on RPD which in turn may lead to routing protocol flaps. If a system with sensor-based-stats enabled receives a specific LDP FEC this can lead to the above condition. Continued receipted of such an LDP FEC will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS 19.2 version 19.2R2 and later versions prior to 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3-S2; 20.1 versions prior to 20.1R2-S1, 20.1R3; 20.2 versions prior to 20.2R2-S1, 20.2R3; 20.3 versions prior to 20.3R1-S2, 20.3R2. This issue does not affect Juniper Networks Junos OS versions prior to 19.2R2. Juniper Networks Junos OS Evolved All versions prior to 20.1R2-S3-EVO; 20.3 versions prior to 20.3R1-S2-EVO.

Scores

CVSS scores of CVE-2021-31363, by who scored it
Scored byCVSSScoreVector
juniperCNA (assigner)3.1Medium6.5CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVDNVD · Modified3.1Medium6.5CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS (exploitation in 30 days)
0.40% · top 65% of all CVEs (6 Nov 2026)
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.5.

Weakness

Affected products

  • Juniper Networks · Junos OS

    • unaffected unspecified – < 19.2R2
    • affected 19.2R2 – < 19.2*
    • affected 19.3 – < 19.3R2-S6, 19.3R3-S2
    • affected 19.4 – < 19.4R1-S4, 19.4R2-S4, 19.4R3-S2
    • affected 20.1 – < 20.1R2-S1, 20.1R3
    • affected 20.2 – < 20.2R2-S1, 20.2R3
    • affected 20.3 – < 20.3R1-S2, 20.3R2

  • Juniper Networks · Junos OS Evolved

    • affected unspecified – < 20.1R2-S3-EVO
    • affected 20.3 – < 20.3R1-S2-EVO

What to do

Solution: The following software releases have been updated to resolve this specific issue in Junos OS: 19.2R3-S3, 19.3R2-S6, 19.3R3-S2, 19.4R1-S4, 19.4R2-S4, 19.4R3-S2, 20.1R2-S1, 20.1R3, 20.2R2-S1, 20.2R3, 20.3R1-S2, 20.3R2, 20.4R1, and all subsequent releases. The following software releases have been updated to resolve this specific issue in Junos OS Evolved: 20.1R2-S3-EVO, 20.3R1-S2-EVO, 20.4R1-EVO, and all subsequent releases.

Workaround: For Junos OS turn off sensor-based-stats by deleting: [protocols ldp traffic-statistics sensor-based-stats] For Junos OS Evolved mLDP will have to be turned off as sensor-based-stats is the default: [protocols ldp p2mp]

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

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .