CVE-2021-31369Network attack vector

Partial service interruption via unthrottled traffic processing

Published Oct 19, 2021 · Updated Sep 16, 2024

Resource exhaustion in Juniper Networks Junos OS on affected MX Series releases allows remote attackers to cause sustained traffic loss. An MS-MPC or MS-MIC service-set with an attached CoS rule fails to limit resources while processing a high rate of specific traffic, causing other serviced traffic to be dropped. Exploitation requires the affected hardware and service-set configuration; the reported consequence is partial denial of service without data disclosure or modification.

CVSS severity5.3
Medium
EPSS probability0.97%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Juniper Networks Junos OS on affected MX Series releases allows remote attackers to cause sustained traffic loss. An MS-MPC or MS-MIC service-set with an attached CoS rule fails to limit resources while processing a high rate of specific traffic, causing other serviced traffic to be dropped. Exploitation requires the affected hardware and service-set configuration; the reported consequence is partial denial of service without data disclosure or modification.

The record

CVE
CVE-2021-31369
Published
Oct 19, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-770, T1499.002
Attack vector
network
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

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

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=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-S7, 19.3R3-S3; version=19.4 <19.4R3-S5; 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-S1, 20.4R3; version=21.1 <21.1R1-S1, 21.1R2; version=unspecified <17.4R3-S5

Published CVSS scores

4.3NIST NVDAV:N/AC:M/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
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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