dbcve.org
JunosOperating system · Juniper

CVE-2021-0287

MEDIUM · 6.5 CVSS v3.1 Published 2021-07-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
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
In a Segment Routing ISIS (SR-ISIS)/MPLS environment, on Juniper Networks Junos OS and Junos OS Evolved devices, configured with ISIS Flexible Algorithm for Segment Routing and sensor-based statistics, a flap of a ISIS link in the network, can lead to a routing process daemon (RPD) crash and restart, causing a Denial of Service (DoS). Continued link flaps will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS: 19.4 versions prior to 19.4R1-S4, 19.4R3-S2; 20.1 versions prior to 20.1R2-S1, 20.1R3; 20.2 versions prior to 20.2R2-S2, 20.2R3; 20.3 versions prior to 20.3R2; Juniper Networks Junos OS Evolved: 20.3-EVO versions prior to 20.3R2-EVO; 20.4-EVO versions prior to 20.4R2-EVO. This issue does not affect: Juniper Networks Junos OS releases prior to 19.4R1. Juniper Networks Junos OS Evolved releases prior to 19.4R1-EVO.

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

In Junos OS/Evolved devices with Segment Routing ISIS (SR-ISIS)/MPLS, ISIS Flexible Algorithm for Segment Routing, and sensor-based statistics configured, a flap of an ISIS link can trigger a crash and restart of the routing process daemon (RPD), causing Denial of Service. Repeated link flaps create a sustained DoS condition.

MitigationUpgrade to Junos OS versions 19.4R1-S4, 19.4R3-S2, 20.1R2-S1, 20.1R3, 20.2R2-S2, 20.2R3, 20.3R2 or later; or Junos OS Evolved versions 20.3R2-EVO, 20.4R2-EVO or later.

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:= 19.4= 20.1= 20.2= 20.3
Junos Os EvolvedOperating system
Affected:= 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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/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. Check Junos OS/Evolved version
    Run 'show version' command to identify the installed Junos version
    Affected if Version is 19.4 (any R variant), 20.1 (any R variant), 20.2 (any R variant), 20.3 (any R variant), 20.4 (any R variant), or 20.3-EVO/20.4-EVO on Evolved variants (compare against the affected versions listed in the CVE)
  2. Verify ISIS protocol is enabled
    Run 'show configuration protocols isis' to check if ISIS is configured
    Affected if ISIS protocol is not configured on the device (if ISIS is not configured, the vulnerability does not apply)
  3. Confirm Segment Routing over ISIS (SR-ISIS) is configured
    Run 'show configuration protocols isis | display set' and look for 'source-packet-routing' or 'segment-routing' statements under the ISIS configuration
    Affected if SR-ISIS (source-packet-routing or segment-routing) is configured under the ISIS protocol - this is required for the vulnerability to be exploitable
  4. Verify MPLS is configured
    Run 'show configuration protocols mpls' to confirm MPLS is enabled on the device
    Affected if MPLS protocol is configured - this is required in combination with SR-ISIS for the flaw
  5. Check for ISIS Flexible Algorithm configuration
    Run 'show configuration protocols isis flexible-algorithm' or look for 'flexible-algorithm' statements in the ISIS configuration
    Affected if Flexible Algorithm for Segment Routing is configured under the ISIS protocol settings
  6. Confirm sensor-based statistics are enabled
    Run 'show configuration services analytics' or look for 'sensor' configurations under services analytics, or check for 'sensor-based-stats' in the configuration
    Affected if Sensor-based statistics collection is configured on the device (this feature combined with the above conditions creates the vulnerable configuration)

The device is affected if it runs an affected Junos OS/Evolved version AND has ISIS configured with SR-ISIS, MPLS, Flexible Algorithm, and sensor-based statistics all simultaneously enabled - link flaps on ISIS adjacencies can then trigger RPD crashes.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to Junos OS versions 19.4R1-S4, 19.4R3-S2, 20.1R2-S1, 20.1R3, 20.2R2-S2, 20.2R3, 20.3R2 or later; or Junos OS Evolved versions 20.3R2-EVO, 20.4R2-EVO or later.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,120
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,392.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-0287 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-0287 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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