Security readout for executives and security teams
Plain-English summary
Some Juniper Junos OS Evolved firewall rules may silently fail when stateless filters use policer actions with certain option combinations. The business risk is that intended network traffic controls may not be enforced, weakening segmentation or rate-control assumptions.
Executive priority
Prioritize remediation where affected devices enforce perimeter, segmentation, tenant, or abuse-control policies. This is not rated critical, but failed network controls can create business exposure if teams assume filters are working.
Technical view
CVE-2021-0225 is an improper exceptional-condition handling issue in Junos OS Evolved. Affected stateless IP firewall filter configurations using 'policer' with certain other options may not take effect. Junos OS is explicitly not affected.
Likely exposure
Exposure is limited to Juniper Networks devices running Junos OS Evolved 19.1R1-EVO and later before 20.3R1-S2-EVO or 20.3R2-EVO, with affected stateless firewall filter configurations using policer actions.
Exploitation context
The source bundle does not report active exploitation, and this CVE is not listed as KEV. The practical risk is control failure rather than code execution: traffic handling may differ from the administrator's intended policy.
Researcher notes
Evidence is limited to the CVE record and Juniper advisory reference. The stated impact is low integrity with no confidentiality or availability impact in CVSS. Validate through configuration review and vendor log indicators, not exploit reproduction.
Mitigation direction
- Upgrade affected Junos OS Evolved systems to 20.3R1-S2-EVO, 20.3R2-EVO, or later vendor-advised fixed releases.
- Review Juniper advisory JSA11120 for platform-specific remediation guidance before maintenance.
- Avoid unsupported policer filter combinations where feasible until upgraded and validated.
- Treat dependent segmentation or rate-control policies as unreliable until enforcement is confirmed.
Validation and detection
- Inventory Junos OS Evolved versions and confirm whether Junos OS, not Evolved, is excluded.
- Identify stateless firewall filters using the policer action with additional options.
- Check kfirewall-agent.log for 'ERROR: filter not supported' on affected devices.
- Confirm intended filters are active after upgrade or configuration adjustment.
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-2021-0225 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
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:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.8MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://kb.juniper.net/JSA11120CVE reference · x_refsource_MISC
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.