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JunosOperating system · Juniper

CVE-2021-0266

CRITICAL · 9.8 CVSS v3.1 Published 2021-04-22
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
The use of multiple hard-coded cryptographic keys in cSRX Series software in Juniper Networks Junos OS allows an attacker to take control of any instance of a cSRX deployment through device management services. This issue affects: Juniper Networks Junos OS on cSRX Series: All versions prior to 20.2R3; 20.3 versions prior to 20.3R2; 20.4 versions prior to 20.4R2.

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

Multiple hard-coded cryptographic keys in Juniper cSRX Series containerized firewall software allow remote attackers to take control of any cSRX instance through device management services by using the known static cryptographic secrets to authenticate or decrypt traffic.

MitigationUpgrade Junos OS on cSRX Series to version 20.2R3, 20.3R2, 20.4R2 or later to remove the hard-coded keys. If immediate patching is not possible, restrict access to device management services using network segmentation or firewall rules.

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:= 20.2= 20.3= 20.4

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
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/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. Identify cSRX Series hardware or virtual instance
    Run 'show chassis hardware' or check system documentation to confirm the device is a cSRX containerized firewall Series model
    Affected if The device is NOT a cSRX Series model - other Juniper products are not affected by this specific hard-coded key vulnerability
  2. Check installed Junos OS version
    Execute 'show version' or 'show version detail' at the Junos CLI prompt and note the exact version number displayed
    Affected if The installed Junos version equals exactly 20.2, 20.3, or 20.4 - only these specific versions contain the hard-coded cryptographic keys
  3. Verify device management services are enabled
    At the Junos CLI, run 'show configuration system services' to view enabled management protocols such as SSH, NETCONF, or web management, and check 'show configuration interfaces' for management IP assignments
    Affected if Any device management service (SSH, NETCONF, web UI) is enabled and reachable - this exposes the cSRX to authentication using the hard-coded keys
  4. Check network exposure of management interfaces
    Review firewall filter configurations and interface policies using 'show configuration firewall' and 'show configuration interfaces' to determine if management interfaces are exposed to untrusted networks
    Affected if Management services are accessible from non-internal networks - remote attackers can exploit the hard-coded keys over exposed management channels

A cSRX Series device running Junos version 20.2, 20.3, or 20.4 with device management services enabled and network accessibility is vulnerable to remote compromise via the hard-coded cryptographic keys.

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 on cSRX Series to version 20.2R3, 20.3R2, 20.4R2 or later to remove the hard-coded keys. If immediate patching is not possible, restrict access to device management services using network segmentation or firewall rules.

Recommended fix High confidence

Upgrade to Junos OS 20.2R3, 20.3R2, 20.4R2 or later releases on cSRX Series

  1. 1. Identify the current Junos OS version running on the cSRX device using 'show version' command
  2. 2. Confirm the device is running a vulnerable version (20.2, 20.3, or 20.4 before the R2/R3 releases)
  3. 3. Backup the current configuration using 'request system configuration rescue save' or 'file copy' to external storage
  4. 4. Review the Junos release notes for 20.2R3, 20.3R2, or 20.4R2 (whichever branch you plan to upgrade to) for any specific upgrade requirements
  5. 5. Download the appropriate Junos software image for cSRX from the Juniper Networks support portal
  6. 6. Transfer the software image to the cSRX device
  7. 7. Initiate the upgrade using 'request system software add <package-name>' command
  8. 8. Reboot the device after upgrade completes using 'request system reboot'
Caveat Standard Junos upgrade considerations apply - review release notes for any configuration changes or compatibility notices before upgrading

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

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,780
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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-2021-0266 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