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JunosOperating system · Juniper

CVE-2021-0284

HIGH · 7.5 CVSS v3.1 Published 2021-08-17
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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
A buffer overflow vulnerability in the TCP/IP stack of Juniper Networks Junos OS allows an attacker to send specific sequences of packets to the device thereby causing a Denial of Service (DoS). By repeatedly sending these sequences of packets to the device, an attacker can sustain the Denial of Service (DoS) condition. The device will abnormally shut down as a result of these sent packets. A potential indicator of compromise will be the following message in the log files: "eventd[13955]: SYSTEM_ABNORMAL_SHUTDOWN: System abnormally shut down" This issue is only triggered by traffic destined to the device. Transit traffic will not trigger this issue. This issue affects: Juniper Networks Junos OS 12.3 versions prior to 12.3R12-S19; 15.1 versions prior to 15.1R7-S10; 17.3 versions prior to 17.3R3-S12; 18.4 versions prior to 18.4R2-S9, 18.4R3-S9; 19.1 versions prior to 19.1R3-S7; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S7, 19.3R3-S3; 19.4 versions prior to 19.4R3-S5; 20.1 versions prior to 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3-S1; 20.4 versions prior to 20.4R2-S2, 20.4R3; 21.1 versions prior to 21.1R2; 21.2 versions prior to 21.2R1-S1, 21.2R2.

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 buffer overflow vulnerability exists in the TCP/IP stack of Juniper Networks Junos OS. An attacker can send specific sequences of packets destined to the device, triggering the overflow which causes the system to abnormally shut down. Repeated packet sequences can sustain the DoS condition. The issue only affects traffic destined to the device, not transit traffic.

MitigationApply the vendor-supplied software patches for the specific Junos OS version. Until patched, consider implementing network segmentation or access controls to limit exposure of affected devices to untrusted networks.

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:= 12.3= 15.1= 17.3= 18.4= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3= 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
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 Junos OS version
    Execute 'show version' or 'show system information' on the device CLI and note the software version string
    Affected if The displayed version matches one of the affected releases: 12.3, 15.1, 17.3, 18.4, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, 20.4, or 21.1
  2. Determine network exposure
    Review the device interface configuration using 'show configuration interfaces' and check which interfaces are assigned to which security zones via 'show security zones'
    Affected if Any interface directly connected to untrusted or external networks (such as internet-facing interfaces) is operational and processing traffic destined to the device
  3. Verify TCP processing is enabled
    Confirm that the device is configured as a routing platform with TCP/IP stack active; this is default for Junos but can be verified with 'show system services'
    Affected if TCP/IP stack processing is enabled, which is the default state for Junos devices acting as routers or firewalls

You are affected if your Junos OS version matches one of the listed affected versions and the device has directly accessible network interfaces receiving traffic from untrusted sources.

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

Apply the vendor-supplied software patches for the specific Junos OS version. Until patched, consider implementing network segmentation or access controls to limit exposure of affected devices to untrusted networks.

Recommended fix High confidence

12.3R12-S19, 15.1R7-S10, 17.3R3-S12, or 18.4R2-S9/18.4R3-S9 (depending on current branch)

  1. 1. Identify the current Junos OS version running on the device using 'show version' command
  2. 2. Determine the appropriate fixed version based on the current branch: for 12.3 upgrade to 12.3R12-S19, for 15.1 upgrade to 15.1R7-S10, for 17.3 upgrade to 17.3R3-S12, for 18.4 upgrade to 18.4R2-S9 or 18.4R3-S9
  3. 3. Download the appropriate Junos software package from the Juniper Networks support portal (kb.juniper.net)
  4. 4. Transfer the software package to the device using FTP, SCP, or USB media
  5. 5. Initiate the software installation using 'request system software add <package-name>' command
  6. 6. Reboot the device after installation completes using 'request system reboot' command
  7. 7. Verify the upgrade was successful by running 'show version' and confirm the fixed version is installed
  8. 8. Check system logs to confirm no abnormal shutdowns occur and the vulnerability is resolved
Caveat Upgrading Junos OS may require feature reconfiguration; test in lab environment before production deployment

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-2021-0284 in production — separate from our analysis above.

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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