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CVE-2021-31353

Junos OS and Junos OS Evolved: RPD core upon receipt of specific BGP update

High7.5EPSS 1.2%
Published
Updated
Reserved
Assigned by
juniper

Description

An Improper Handling of Exceptional Conditions vulnerability in Juniper Networks Junos OS and Junos OS Evolved allows an attacker to inject a specific BGP update, causing the routing protocol daemon (RPD) to crash and restart, leading to a Denial of Service (DoS). Continued receipt and processing of the BGP update will create a sustained Denial of Service (DoS) condition. This issue affects very specific versions of Juniper Networks Junos OS: 19.3R3-S2; 19.4R3-S3; 20.2 versions 20.2R2-S3 and later, prior to 20.2R3-S2; 20.3 versions 20.3R2 and later, prior to 20.3R3; 20.4 versions 20.4R2 and later, prior to 20.4R3; 21.1 versions prior to 21.1R2. Juniper Networks Junos OS 20.1 is not affected by this issue. This issue also affects Juniper Networks Junos OS Evolved: All versions prior to 20.4R2-S3-EVO, 20.4R3-EVO; 21.1-EVO versions prior to 21.1R2-EVO; 21.2-EVO versions prior to 21.2R2-EVO.

Scores

CVSS scores of CVE-2021-31353, by who scored it
Scored byCVSSScoreVector
juniperCNA (assigner)3.1High7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVDNVD · Modified3.1High7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS (exploitation in 30 days)
1.2% · top 32% of all CVEs (7 Nov 2026)
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.

Weakness

Affected products

  • Juniper Networks · Junos OS

    • unaffected unspecified – < 19.3R3-S2
    • affected 19.3R3-S2
    • affected 19.4R3-S3
    • unaffected 20.1R1 – < 20.1*
    • unaffected 20.2 – < 20.2R2-S3
    • unaffected 20.3 – < 20.3R2
    • unaffected 20.4 – < 20.4R2
    • affected 21.1 – < 21.1R2

  • Juniper Networks · Junos OS Evolved

    • affected unspecified – < 20.4R2-S3-EVO, 20.4R3-EVO
    • affected 21.1-EVO – < 21.1R2-EVO
    • affected 21.2-EVO – < 21.2R2-EVO

What to do

Solution: The following software releases have been updated to resolve this specific issue: Junos OS 18.4R2-S9, 19.1R3-S7, 19.3R3-S3, 19.4R1-S4, 19.4R3-S4, 20.1R3, 20.2R3-S2, 20.3R3, 20.4R3, 21.1R2, 21.2R1, 21.2R2, 21.3R1, and all subsequent releases. Junos OS Evolved 20.4R2-S3-EVO, 20.4R3-EVO, 21.1R2-EVO, 21.2R2-EVO, 21.3R1-EVO, 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.

Workaround: This issue can be mitigated in two ways: 1) ensure that TTL propagation is either enabled or disabled in both places below: protocols mpls no-propagate-ttl routing-instance <vrf> no-vrf-propagate-ttl 2) Disable multipath: routing-instance <vrf> routing-options multipath

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 .