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JunosOperating system · Juniper

CVE-2021-31384

CRITICAL · 10.0 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 →
100/100
Remediation priority · Urgent
Remotely reachable 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
Due to a Missing Authorization weakness and Insufficient Granularity of Access Control in a specific device configuration, a vulnerability exists in Juniper Networks Junos OS on SRX Series whereby an attacker who attempts to access J-Web administrative interfaces can successfully do so from any device interface regardless of the web-management configuration and filter rules which may otherwise protect access to J-Web. This issue affects: Juniper Networks Junos OS SRX Series 20.4 version 20.4R1 and later versions prior to 20.4R2-S1, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2. This issue does not affect Juniper Networks Junos OS versions prior to 20.4R1.

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

A Missing Authorization and Insufficient Granularity of Access Control vulnerability in Juniper Junos OS SRX Series allows attackers to bypass web-management configuration and filter rules to access J-Web administrative interfaces from any device interface, regardless of intended access controls.

MitigationUpgrade Junos OS to version 20.4R2-S1, 20.4R3, 21.1R1-S1, 21.1R2 or later. Alternatively, disable J-Web if not required.

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:= 20.4= 21.1

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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. Confirm J-Web is enabled
    Run 'show system services web-management' to see if J-Web or HTTP/HTTPS management is configured
    Affected if web-management service is enabled (output shows http or https configured)
  2. Verify Junos OS version
    Run 'show version' and check the installed Junos version number
    Affected if version is 20.4 or 21.1 (base releases) or falls within the affected ranges for this CVE
  3. Check web-management interface bindings
    Run 'show configuration system services web-management' and look for interface specifications
    Affected if J-Web is bound to interfaces that were not intentionally allowed or bound to 'any' interface
  4. Review J-Web access-filter rules
    Run 'show configuration firewall filter J-Web' or similar filter configurations to inspect access control rules
    Affected if filter rules exist but can be bypassed or no specific interface restrictions are defined

A user is affected if Junos OS version 20.4 or 21.1 is running AND J-Web web-management interface is enabled and accessible from unintended interfaces.

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

Upgrade Junos OS to version 20.4R2-S1, 20.4R3, 21.1R1-S1, 21.1R2 or later. Alternatively, disable J-Web if not required.

Recommended fix High confidence

20.4R2-S1, 20.4R3, 21.1R1-S1, 21.1R2, or later releases

  1. Upgrade Junos OS on SRX Series to version 20.4R2-S1 or later (20.4R3 or higher)
  2. Alternatively, upgrade to version 21.1R1-S1 or later (21.1R2 or higher)
  3. After upgrade, verify J-Web access control by testing that web-management configuration and filter rules are properly enforced
  4. Confirm the fix by reviewing release notes for CVE-2021-31384

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

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2021-31384 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data