CVE-2021-31362

Routing disruption via spoofed IS-IS hello PDU

Published Oct 19, 2021 · Updated Sep 17, 2024

Protection mechanism failure in RPD in Junos OS and Junos OS Evolved allows attackers to interrupt IS-IS routing via a spoofed hello PDU. RPD processes the spoofed PDU against an established adjacency and takes that adjacency down rather than preserving it. The attacker must be adjacent to an IS-IS-enabled interface; continued spoofed PDUs sustain the routing disruption, with no reported confidentiality or integrity impact.

CVSS severity6.5
Medium
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Protection mechanism failure in RPD in Junos OS and Junos OS Evolved allows attackers to interrupt IS-IS routing via a spoofed hello PDU. RPD processes the spoofed PDU against an established adjacency and takes that adjacency down rather than preserving it. The attacker must be adjacent to an IS-IS-enabled interface; continued spoofed PDUs sustain the routing disruption, with no reported confidentiality or integrity impact.

The record

CVE
CVE-2021-31362
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-693, T1498
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=21.1 <21.1R2-EVO
  2. Affected versionversion=unspecified <20.4R2-EVO

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=21.1 <21.1R2-EVO; version=unspecified <20.4R2-EVO
Juniper Networks · Junos OSversion=18.3 <18.3R3-S5; version=18.4 <18.4R3-S9; version=19.1 <19.1R3-S7; version=19.2 <19.2R1-S7, 19.2R3-S3; version=19.3 <19.3R2-S6, 19.3R3-S2; version=19.4 <19.4R3-S3; version=20.1 <20.1R3; version=20.2 <20.2R3; version=20.3 <20.3R3; version=20.4 <20.4R2; version=unspecified <18.2R3-S8

Published CVSS scores

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

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-693Protection Mechanism Failure
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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