CVE-2021-31351Network attack vector

Line-card reset via exceptional packet handling

Published Oct 19, 2021 · Updated Sep 17, 2024

Improper exceptional-condition handling in affected Junos OS releases on MX Series allows remote attackers to reset an MS-MPC or MS-MIC. Packet processing on either module fails to handle a specific packet safely and responds by resetting the line card. No authentication or user interaction is required, and continued packet delivery sustains the service interruption.

CVSS severity7.5
High
EPSS probability1.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper exceptional-condition handling in affected Junos OS releases on MX Series allows remote attackers to reset an MS-MPC or MS-MIC. Packet processing on either module fails to handle a specific packet safely and responds by resetting the line card. No authentication or user interaction is required, and continued packet delivery sustains the service interruption.

The record

CVE
CVE-2021-31351
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-754, T1499.004
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=17.3R3-S11
  2. Affected versionversion=17.4R2-S13 <17.4*
  3. Affected versionversion=18.1R3-S12
  4. Affected versionversion=18.2R2-S8, 18.2R3-S7 <18.2*
  5. Affected versionversion=18.3R3-S4
  6. Affected versionversion=18.4R1-S8, 18.4R2-S7 <18.4*
  7. Affected versionversion=18.4R3-S7
  8. Affected versionversion=19.1R3-S4, 19.1R3-S5
  9. Affected versionversion=19.2R1-S6
  10. Affected versionversion=19.3R3-S2
  11. Affected versionversion=19.4R2-S4 <19.4*
  12. Affected versionversion=19.4R3-S2
  13. Affected versionversion=20.1R2-S1
  14. Affected versionversion=20.2R2-S2 <20.2*
  15. Affected versionversion=20.2R3
  16. Affected versionversion=20.3R1-S2 <20.3*
  17. Affected versionversion=20.3R2
  18. Affected versionversion=20.4 <20.4R2-S1, 20.4R3
  19. Affected versionversion=21.1 <21.1R1-S1, 21.1R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

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

Published CVSS scores

7.5Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
T1499.004Application or System Exploitation

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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