Security readout for executives and security teams
Plain-English summary
This vulnerability can make affected Juniper routing devices restart their routing process when a specific SR-ISIS/MPLS setup experiences ISIS link flapping. The business impact is availability: routing disruption or sustained denial of service if link instability continues. It is not described as data theft or unauthorized access.
Executive priority
Treat this as a targeted availability risk for critical routing infrastructure. Prioritize remediation on backbone or service-impacting Juniper devices that match the affected configuration, especially where routing process restarts would disrupt customer or internal connectivity.
Technical view
CVE-2021-0287 affects Junos OS and Junos OS Evolved in SR-ISIS/MPLS environments using ISIS Flexible Algorithm for Segment Routing and sensor-based statistics. An ISIS link flap can crash and restart RPD. Continued flaps can sustain denial of service. CVSS 3.1 is 6.5 with high availability impact.
Likely exposure
Exposure is likely limited to Juniper networks running affected Junos OS or Junos OS Evolved releases with SR-ISIS/MPLS, ISIS Flexible Algorithm, and sensor-based statistics enabled. This is most relevant to service provider, backbone, and advanced enterprise routing environments, not typical edge-only deployments.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. The triggering condition is an ISIS link flap in the affected network configuration. Repeated flaps can prolong denial of service, but no public exploit activity is cited in the provided sources.
Researcher notes
CVSS indicates adjacent attack vector, low complexity, no privileges, no user interaction, and high availability impact. Affected versions include specific 19.4, 20.1, 20.2, 20.3, and EVO 20.3/20.4 trains. The sources do not provide exploit details or workaround confirmation beyond fixed releases.
Mitigation direction
- Upgrade affected Junos OS releases to the fixed versions identified by Juniper.
- Upgrade affected Junos OS Evolved releases to the fixed EVO versions identified by Juniper.
- Prioritize devices using SR-ISIS/MPLS with ISIS Flexible Algorithm and sensor-based statistics.
- Review Juniper advisory JSA11189 before choosing an upgrade path.
- Monitor and investigate repeated ISIS link flaps until remediation is complete.
Validation and detection
- Inventory Juniper devices and record Junos OS or Junos OS Evolved versions.
- Confirm whether SR-ISIS/MPLS, ISIS Flexible Algorithm, and sensor-based statistics are enabled.
- Check operational logs for RPD crashes or restarts near ISIS link flaps.
- Verify upgraded devices run a non-affected release from the advisory.
- Track recurrence of ISIS flaps and RPD restarts after remediation.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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Open ATT&CK lookupCVE-2021-0287 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H2.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11189CVE reference · x_refsource_CONFIRM
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Check for Unusual or Exceptional Conditions
Improper Check for Unusual or Exceptional Conditions represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.