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JunosOperating system · Juniper

CVE-2021-31354

HIGH · 8.8 CVSS v3.1 Published 2021-10-19
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
93/100
Remediation priority · Urgent
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An Out Of Bounds (OOB) access vulnerability in the handling of responses by a Juniper Agile License (JAL) Client in Juniper Networks Junos OS and Junos OS Evolved, configured in Network Mode (to use Juniper Agile License Manager) may allow an attacker to cause a partial Denial of Service (DoS), or lead to remote code execution (RCE). The vulnerability exists in the packet parsing logic on the client that processes the response from the server using a custom protocol. An attacker with control of a JAL License Manager, or with access to the local broadcast domain, may be able to spoof a new JAL License Manager and/or craft a response to the Junos OS License Client, leading to exploitation of this vulnerability. This issue only affects Junos systems configured in Network Mode. Systems that are configured in Standalone Mode (the default mode of operation for all systems) are not vulnerable to this issue. This issue affects: Juniper Networks Junos OS: 19.2 versions prior to 19.2R3-S3; 19.3 versions prior to 19.3R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2. Juniper Networks Junos OS Evolved: version 20.1R1-EVO and later versions, prior to 21.2R2-EVO. This issue does not affect Juniper Networks Junos OS versions prior to 19.2R1.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

An Out Of Bounds (OOB) access vulnerability exists in the Juniper Agile License (JAL) Client packet parsing logic when processing responses from a JAL License Manager server using a custom protocol. An attacker with control of a JAL License Manager or access to the local broadcast domain can craft malicious responses that trigger the OOB access, potentially causing DoS or achieving remote code execution. Only systems configured in Network Mode are affected; Standalone Mode (the default) is not vulnerable.

MitigationEnsure Junos devices are operating in Standalone Mode (the default), or apply the vendor-provided patches to the specific affected versions listed in the advisory. If Network Mode is required, ensure the JAL License Manager is on a trusted network segment and consider network segmentation to prevent spoofing attacks.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 19.2= 19.3= 20.1= 20.2= 20.3= 20.4= 21.1
Junos Os EvolvedOperating system
Affected:= 20.1= 20.2= 20.3= 20.4= 21.1= 21.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Junos version
    Execute 'show version' or 'show version detail' on the device CLI to obtain the installed Junos version
    Affected if The version matches one of the affected releases: 19.2, 19.3, 20.1, 20.2, 20.3, 20.4, 21.1 for Junos; or 20.1, 20.2, 20.3, 20.4, 21.1, 21.2 for Junos OS Evolved
  2. Verify JAL mode configuration
    Execute 'show system license' or 'show configuration system license' to determine if the Juniper Agile License client is configured in Network Mode or Standalone Mode
    Affected if The JAL client is configured in Network Mode (not Standalone Mode) - only Network Mode is vulnerable
  3. Confirm JAL License Manager status
    Review the license manager configuration to determine if a remote JAL License Manager server is configured, which is required for Network Mode operation
    Affected if A remote JAL License Manager server is defined in the configuration, indicating Network Mode is active

The device is affected if it runs an affected Junos version AND has JAL configured in Network Mode; the default Standalone Mode configuration is not vulnerable.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Ensure Junos devices are operating in Standalone Mode (the default), or apply the vendor-provided patches to the specific affected versions listed in the advisory. If Network Mode is required, ensure the JAL License Manager is on a trusted network segment and consider network segmentation to prevent spoofing attacks.

Recommended fix High confidence

Junos OS: 19.2R3-S3, 19.3R3-S3, 20.1R3-S1, 20.2R3-S2, 20.3R3, 20.4R3, or 21.1R2+; Junos OS Evolved: 21.2R2-EVO+

  1. 1. Verify current Junos OS/Junos OS Evolved version with 'show version' command
  2. 2. Determine if the system is configured in Network Mode (using Juniper Agile License Manager) with 'show system license' or 'show configuration | display set | match license'
  3. 3. If in Network Mode, plan upgrade to fixed release: Junos OS 19.2R3-S3+, 19.3R3-S3+, 20.1R3-S1+, 20.2R3-S2+, 20.3R3+, 20.4R3+, or 21.1R2+; Junos OS Evolved to 21.2R2-EVO or later
  4. 4. Alternatively, if Network Mode is not required, switch to Standalone Mode (default) which is not vulnerable - remove Network Mode configuration with 'delete system license network-mode' and commit
  5. 5. After upgrade or config change, verify the fix with 'show version' and confirm Network Mode is disabled or system is on fixed version
Caveat Upgrade to a different release train may introduce compatibility concerns; review release notes for any behavioral changes before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
30.0 hours of engineering $5,280
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-31354 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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