CVE-2021-31363

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

MEDIUM

6.5

CVSS Score

Published: October 19, 2021 at 06:16 PM UTC

Updated: June 17, 2026 at 03:51 AM UTC

3 products affected across 2 vendorsJunosJunos OS EvolvedJunos OS Evolved

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Severity

MEDIUM6.5

Exploit prediction

EPSS 0.4%

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Junos OS Evolved · Juniper

95%

20.1 r1 20.1 r1-s1 20.1 r2 20.1 r2-s1 20.1 r2-s2 20.2 r1 20.2 r1-s1 20.2 r2 20.3 r1 20.3 r1-s1

Junos · Juniper Networks

95%

19.2R2 ≤ v < 19.2*19.3 ≤ v < 19.3R2-S6, 19.3R3-S219.4 ≤ v < 19.4R1-S4, 19.4R2-S4, 19.4R3-S220.1 ≤ v < 20.1R2-S1, 20.1R320.2 ≤ v < 20.2R2-S1, 20.2R320.3 ≤ v < 20.3R1-S2, 20.3R219.2 r2 19.2 r2-s1 19.2 r3 19.2 r3-s1 19.2 r3-s2 19.2R2 19.3 19.3 r1 19.3 r1-s1 19.3 r2 19.3 r2-s1 19.3 r2-s2 19.3 r2-s3 19.3 r2-s4 19.3 r2-s5 19.3 r3-s2 19.4 19.4 r1 19.4 r1-s1 19.4 r1-s2 19.4 r1-s3 19.4 r2-s4 19.4 r3-s2 20.1 20.1 r1 20.1 r1-s1 20.1 r1-s2 20.1 r1-s3 20.1 r1-s4 20.1 r2 20.1 r3 20.2 20.2 r1 20.2 r1-s1 20.2 r1-s2 20.2 r1-s3 20.2 r2 20.2 r3 20.3 20.3 r1 20.3 r1-s1 20.3 r2

Affected range stops below 19.2*, so it looks safe — our inference, not a vendor statement

Vendor states this is fixed in 19.2R2 (unaffected)

Affected range stops below 19.3R2-S6, 19.3R3-S2, so it looks safe — our inference, not a vendor statement

Affected range stops below 19.4R1-S4, 19.4R2-S4, 19.4R3-S2, so it looks safe — our inference, not a vendor statement

Affected range stops below 20.1R2-S1, 20.1R3, so it looks safe — our inference, not a vendor statement

Affected range stops below 20.2R2-S1, 20.2R3, so it looks safe — our inference, not a vendor statement

Affected range stops below 20.3R1-S2, 20.3R2, so it looks safe — our inference, not a vendor statement

Junos OS Evolved · Juniper Networks

60%

v < 20.1R2-S3-EVO20.3 ≤ v < 20.3R1-S2-EVO20.3

Affected range stops below 20.1R2-S3-EVO, so it looks safe — our inference, not a vendor statement

Affected range stops below 20.3R1-S2-EVO, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://kb.juniper.net/JSA11225

References (1)

x_refsource_CONFIRMPatchVendor Advisory

Source: [email protected]

https://kb.juniper.net/JSA11225

CVSS

6.5MEDIUMjuniper

Attack Vector: ADJACENT_NETWORK
Complexity: LOW
Privileges: NONE
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: NONE
Integrity: NONE
Availability: HIGH

Vector?

Quick Info

StatusMODIFIED

CWE

CWE-835

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