CVE-2021-31382Network attack vector

Firewall bypass via post-upgrade filter assignment race

Published Oct 19, 2021 · Updated Sep 17, 2024

Race condition in Junos OS on PTX1000 and PTX10002-60C systems allows remote attackers to bypass intended firewall filtering after an upgrade. The chassisd and dfwd processes race while applying interface configuration, causing filters to be omitted, substituted, or attached to the wrong logical or physical interface. The condition exists only after upgrading to an affected release, and misassigned filters let traffic that should be blocked propagate and disrupt services.

CVSS severity6.5
Medium
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in Junos OS on PTX1000 and PTX10002-60C systems allows remote attackers to bypass intended firewall filtering after an upgrade. The chassisd and dfwd processes race while applying interface configuration, causing filters to be omitted, substituted, or attached to the wrong logical or physical interface. The condition exists only after upgrading to an affected release, and misassigned filters let traffic that should be blocked propagate and disrupt services.

The record

CVE
CVE-2021-31382
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-362
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=17.2R1 <17.2*
  2. Affected versionversion=17.3 <17.3R3-S12
  3. Affected versionversion=17.4 <17.4R3-S5
  4. Affected versionversion=18.1 <18.1R3-S13
  5. Affected versionversion=18.2 <18.2R3-S8
  6. Affected versionversion=18.3 <18.3R3-S5
  7. Affected versionversion=18.4 <18.4R1-S8, 18.4R2-S8, 18.4R3-S8
  8. Affected versionversion=18.4 <18.4R3-S9
  9. Affected versionversion=19.1 <19.1R3-S5
  10. Affected versionversion=19.1R1 <19.1*
  11. Affected versionversion=19.2 <19.2R3-S2
  12. Affected versionversion=19.3 <19.3R2-S6, 19.3R3-S3
  13. Affected versionversion=19.4 <19.4R2-S4, 19.4R3-S3
  14. Affected versionversion=19.4 <19.4R2-S5, 19.4R3-S5
  15. Affected versionversion=20.1 <20.1R3
  16. Affected versionversion=20.1 <20.1R3-S1
  17. Affected versionversion=20.2 <20.2R2-S3, 20.2R3
  18. Affected versionversion=20.2 <20.2R3-S2
  19. Affected versionversion=20.3 <20.3R2-S1, 20.3R3
  20. Affected versionversion=20.3 <20.3R3-S1
  21. Affected versionversion=20.4 <20.4R1-S1, 20.4R2
  22. Affected versionversion=20.4R1 <20.4*
  23. Affected versionversion=21.1 <21.1R2
  24. Affected versionversion=21.2R1 <21.2*
  25. Affected versionversion=21.3 <21.3R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=17.2R1 <17.2*; version=17.3 <17.3R3-S12; version=17.4 <17.4R3-S5; version=18.1 <18.1R3-S13; version=18.2 <18.2R3-S8; version=18.3 <18.3R3-S5; version=18.4 <18.4R1-S8, 18.4R2-S8, 18.4R3-S8; version=18.4 <18.4R3-S9; version=19.1 <19.1R3-S5; version=19.1R1 <19.1*; version=19.2 <19.2R3-S2; version=19.3 <19.3R2-S6, 19.3R3-S3; version=19.4 <19.4R2-S4, 19.4R3-S3; version=19.4 <19.4R2-S5, 19.4R3-S5; version=20.1 <20.1R3; version=20.1 <20.1R3-S1; version=20.2 <20.2R2-S3, 20.2R3; version=20.2 <20.2R3-S2; version=20.3 <20.3R2-S1, 20.3R3; version=20.3 <20.3R3-S1; version=20.4 <20.4R1-S1, 20.4R2; version=20.4R1 <20.4*; version=21.1 <21.1R2; version=21.2R1 <21.2*; version=21.3 <21.3R2

Published CVSS scores

6.5Juniper Networks, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:L
9.0NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/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.

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-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

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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