CVE-2021-31361Network attack vector

Denial of service via VXLAN packet processing

Published Oct 19, 2021 · Updated Sep 17, 2024

Denial of service in Juniper Networks Junos OS on QFX and PTX Series allows remote attackers to overload FPC CPUs with VXLAN traffic. The forwarding path improperly checks and handles exceptional conditions while encapsulating specific IP packets in VXLAN, increasing FPC CPU utilization. No authentication or user interaction is required; continued receipt of the crafted traffic sustains a partial service interruption.

CVSS severity5.3
Medium
EPSS probability1.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Juniper Networks Junos OS on QFX and PTX Series allows remote attackers to overload FPC CPUs with VXLAN traffic. The forwarding path improperly checks and handles exceptional conditions while encapsulating specific IP packets in VXLAN, increasing FPC CPU utilization. No authentication or user interaction is required; continued receipt of the crafted traffic sustains a partial service interruption.

The record

CVE
CVE-2021-31361
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-754, CWE-755, T1499.002
Attack vector
network
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 <17.4R2-S13, 17.4R3-S4
  2. Affected versionversion=18.1 <18.1R3-S12
  3. Affected versionversion=18.2 <18.2R2-S8, 18.2R3-S7
  4. Affected versionversion=18.3 <18.3R3-S4
  5. Affected versionversion=18.4 <18.4R1-S8, 18.4R2-S7, 18.4R3-S7
  6. Affected versionversion=19.1 <19.1R1-S6, 19.1R2-S2, 19.1R3-S4
  7. Affected versionversion=19.1 <19.1R3-S6
  8. Affected versionversion=19.2 <19.2R1-S6, 19.2R3-S2
  9. Affected versionversion=19.2 <19.2R1-S7, 19.2R3-S3
  10. Affected versionversion=19.3 <19.3R2-S6, 19.3R3-S3
  11. Affected versionversion=19.3 <19.3R3-S1
  12. Affected versionversion=19.4 <19.4R1-S4, 19.4R3-S5
  13. Affected versionversion=19.4 <19.4R2-S3, 19.4R3-S1
  14. Affected versionversion=20.1 <20.1R2, 20.1R3
  15. Affected versionversion=20.1 <20.1R2-S2, 20.1R3
  16. Affected versionversion=20.2 <20.2R2, 20.2R3
  17. Affected versionversion=20.2 <20.2R3-S1
  18. Affected versionversion=20.3 <20.3R1-S1, 20.3R2
  19. Affected versionversion=20.3 <20.3R2-S1, 20.3R3
  20. Affected versionversion=20.4 <20.4R2-S1, 20.4R3
  21. Affected versionversion=21.1 <21.1R1-S1, 21.1R2
  22. Affected versionversion=unspecified <17.3R3-S11
  23. Affected versionversion=unspecified <18.4R3-S9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.4 <17.4R2-S13, 17.4R3-S4; version=18.1 <18.1R3-S12; version=18.2 <18.2R2-S8, 18.2R3-S7; version=18.3 <18.3R3-S4; version=18.4 <18.4R1-S8, 18.4R2-S7, 18.4R3-S7; version=19.1 <19.1R1-S6, 19.1R2-S2, 19.1R3-S4; version=19.1 <19.1R3-S6; version=19.2 <19.2R1-S6, 19.2R3-S2; version=19.2 <19.2R1-S7, 19.2R3-S3; version=19.3 <19.3R2-S6, 19.3R3-S3; version=19.3 <19.3R3-S1; version=19.4 <19.4R1-S4, 19.4R3-S5; version=19.4 <19.4R2-S3, 19.4R3-S1; version=20.1 <20.1R2, 20.1R3; version=20.1 <20.1R2-S2, 20.1R3; version=20.2 <20.2R2, 20.2R3; version=20.2 <20.2R3-S1; version=20.3 <20.3R1-S1, 20.3R2; version=20.3 <20.3R2-S1, 20.3R3; version=20.4 <20.4R2-S1, 20.4R3; version=21.1 <21.1R1-S1, 21.1R2; version=unspecified <17.3R3-S11; version=unspecified <18.4R3-S9

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
CWE-755Improper Handling of Exceptional Conditions
T1499.002Service Exhaustion Flood

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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