CVE-2021-31363

Sustained routing disruption via LDP-triggered RPD loop

Published Oct 19, 2021 · Updated Sep 16, 2024

An infinite loop in RPD in Juniper Networks Junos OS and Junos OS Evolved allows remote attackers to disrupt routing via a crafted LDP FEC. With sensor-based statistics enabled, RPD fails to terminate processing of the specific FEC, driving high daemon load and routing-protocol flaps. The attacker must reach an MPLS P2MP LDP adjacency, and continued delivery sustains the service interruption.

CVSS severity6.5
Medium
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An infinite loop in RPD in Juniper Networks Junos OS and Junos OS Evolved allows remote attackers to disrupt routing via a crafted LDP FEC. With sensor-based statistics enabled, RPD fails to terminate processing of the specific FEC, driving high daemon load and routing-protocol flaps. The attacker must reach an MPLS P2MP LDP adjacency, and continued delivery sustains the service interruption.

The record

CVE
CVE-2021-31363
Published
Oct 19, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-835, T1498
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=20.3 <20.3R1-S2-EVO
  2. Affected versionversion=unspecified <20.1R2-S3-EVO

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=20.3 <20.3R1-S2-EVO; version=unspecified <20.1R2-S3-EVO
Juniper Networks · Junos OSversion=19.2R2 <19.2* changes=[{"at":"19.2R3-S3","status":"unaffected"}]; version=19.3 <19.3R2-S6, 19.3R3-S2; version=19.4 <19.4R1-S4, 19.4R2-S4, 19.4R3-S2; version=20.1 <20.1R2-S1, 20.1R3; version=20.2 <20.2R2-S1, 20.2R3; version=20.3 <20.3R1-S2, 20.3R2

Published CVSS scores

6.5Juniper NetworksCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.3NIST NVDAV:A/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1498Network Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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