CVE-2021-31370

Control traffic loss via multicast input filtering

Published Oct 19, 2021 · Updated Sep 17, 2024

Incomplete input validation in Junos OS on QFX5000 and EX4600 allows adjacent unauthenticated attackers to drop control traffic via multicast floods. The Packet Forwarding Engine fails to reject a high rate of specific multicast packets, so control traffic received from the network is discarded. Continued traffic sustains denial of service against routing and other control protocols; no authentication or user interaction is required, but the attacker must be on an adjacent network.

CVSS severity3.3
Low
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

Incomplete input validation in Junos OS on QFX5000 and EX4600 allows adjacent unauthenticated attackers to drop control traffic via multicast floods. The Packet Forwarding Engine fails to reject a high rate of specific multicast packets, so control traffic received from the network is discarded. Continued traffic sustains denial of service against routing and other control protocols; no authentication or user interaction is required, but the attacker must be on an adjacent network.

The record

CVE
CVE-2021-31370
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-184, T1499.003, T1499
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=17.4 <17.4R3-S5
  2. Affected versionversion=18.3 <18.3R3-S5
  3. Affected versionversion=18.4 <18.4R3-S9
  4. Affected versionversion=19.1 <19.1R3-S6
  5. Affected versionversion=19.2 <19.2R1-S7, 19.2R3-S3
  6. Affected versionversion=19.3 <19.3R2-S6, 19.3R3-S3
  7. Affected versionversion=19.4 <19.4R1-S4, 19.4R3-S3
  8. Affected versionversion=20.1 <20.1R2-S2, 20.1R3-S1
  9. Affected versionversion=20.2 <20.2R3-S2
  10. Affected versionversion=20.3 <20.3R3
  11. Affected versionversion=20.4 <20.4R2-S2, 20.4R3
  12. Affected versionversion=21.1 <21.1R1-S1, 21.1R2
  13. Affected versionversion=unspecified <17.3R3-S12

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.4 <17.4R3-S5; version=18.3 <18.3R3-S5; version=18.4 <18.4R3-S9; version=19.1 <19.1R3-S6; version=19.2 <19.2R1-S7, 19.2R3-S3; version=19.3 <19.3R2-S6, 19.3R3-S3; version=19.4 <19.4R1-S4, 19.4R3-S3; version=20.1 <20.1R2-S2, 20.1R3-S1; version=20.2 <20.2R3-S2; version=20.3 <20.3R3; version=20.4 <20.4R2-S2, 20.4R3; version=21.1 <21.1R1-S1, 21.1R2; version=unspecified <17.3R3-S12

Published CVSS scores

3.3NVDAV:A/AC:L/Au:N/C:N/I:N/A:P
6.5NVDCVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-184Incomplete List of Disallowed Inputs
T1499.003Network Denial of Service
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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