CVE-2021-3499
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 · uneditedA vulnerability was found in OVN Kubernetes in versions up to and including 0.3.0 where the Egress Firewall does not reliably apply firewall rules when there is multiple DNS rules. It could lead to potentially lose of confidentiality, integrity or availability of a service.
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 · moderate confidenceIn OVN Kubernetes versions 0.3.0 and below, the Egress Firewall feature contains a logic flaw where firewall rules fail to apply reliably when multiple DNS rules are configured. This race condition or ordering issue in rule processing could allow traffic that should be blocked to pass through the firewall, potentially exposing services and violating network segmentation policies.
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<= 0.3.0CVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- Low
- Availability
- Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
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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Determine OVN Kubernetes versionIdentify the version of OVN Kubernetes deployed in your cluster. In OpenShift, check the OpenShift Networking Operator or the OVN Kubernetes pods. In upstream Kubernetes, check the ovn-kubernetes components or DaemonSet version labels.Affected if The installed version is 0.3.0 or lower.
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Verify Egress Firewall is enabledConfirm that the Egress Firewall feature is active in your cluster. This typically involves checking for the presence of EgressFirewall custom resources (CRs) or the OVN egress firewall CNI configuration.Affected if Egress Firewall policies are being applied in the cluster.
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Inspect Egress Firewall DNS rule configurationsList all EgressFirewall custom resources in your cluster and examine the dnsName sections. Count the number of DNS-based rules defined across all EgressFirewall policies.Affected if Multiple DNS rules (two or more) are configured in any EgressFirewall policy or across multiple policies.
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Verify rule application orderObserve the actual firewall rules applied to OVN logical switches or routers. Check if DNS-based allow rules are consistently present and not intermittently missing after Egress Firewall policy changes.Affected if DNS-based egress firewall rules are intermittently missing or not consistently applied when multiple DNS rules exist.
You are affected if you are running OVN Kubernetes version 0.3.0 or lower with the Egress Firewall feature enabled and have configured multiple DNS rules in your Egress Firewall policies.
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 OVN Kubernetes to a version beyond 0.3.0 where the Egress Firewall rule application logic has been corrected; alternatively, avoid configuring multiple DNS rules in Egress Firewall policies until the patch can be applied.
- Consultation6.0 h
- Implementation12.0 h
- Testing8.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-3499 — 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-2021-3499 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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