CVE-2021-0225
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 · uneditedAn Improper Check for Unusual or Exceptional Conditions in Juniper Networks Junos OS Evolved may cause the stateless firewall filter configuration which uses the action 'policer' in certain combinations with other options to not take effect. An administrator can use the following CLI command to see the failures with filter configuration: user@device> show log kfirewall-agent.log | match ERROR Jul 23 14:16:03 ERROR: filter not supported This issue affects Juniper Networks Junos OS Evolved: Versions 19.1R1-EVO and above prior to 20.3R1-S2-EVO, 20.3R2-EVO. This issue does not affect Juniper Networks Junos OS.
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 confidenceA logic error in Junos OS Evolved causes firewall filters using the 'policer' action in certain option combinations to fail silently - the filter is configured but does not take effect, allowing traffic to pass unfiltered when it should be rate-limited. The failure is logged as 'filter not supported' in kfirewall-agent.log.
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= 19.1= 19.2= 19.3= 20.1= 20.2= 20.3CVSS 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
- Changed
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Identify Junos OS Evolved versionRun 'show version' or check system firmware version to determine the installed Junos OS Evolved release (e.g., 19.1, 19.2, 19.3, 20.1, 20.2, or 20.3)Affected if The installed version matches 19.1, 19.2, 19.3, 20.1, 20.2, or 20.3 exactly
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Locate firewall filters using policer actionReview firewall filter configurations with 'show configuration' and look for filters that include the 'policer' action in their term definitionsAffected if Any firewall filter is configured with a policer action applied to traffic
If the installed Junos OS Evolved version is one of the affected releases (19.1, 19.2, 19.3, 20.1, 20.2, or 20.3) AND firewall filters with policer action are configured, inspect kfirewall-agent.log for 'filter not supported' messages to confirm exploitation.
Generated from the published advisory. Verify against your own configuration.
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 dataUpgrade Junos OS Evolved to version 20.3R1-S2-EVO or later where the fix is incorporated; no workarounds are documented.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-0225 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-0225 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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