CVE-2025-20316
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 in the access control list (ACL) programming of Cisco IOS XE Software for Cisco Catalyst 9500X and 9600X Series Switches could allow an unauthenticated, remote attacker to bypass a configured ACL on an affected device. This vulnerability is due to the flooding of traffic from an unlearned MAC address on a switch virtual interface (SVI) that has an egress ACL applied. An attacker could exploit this vulnerability by causing the VLAN to flush its MAC address table. This condition can also occur if the MAC address table is full. A successful exploit could allow the attacker to bypass an egress ACL on an affected device.
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 confidenceThis vulnerability in Cisco IOS XE Software for Catalyst 9500X and 9600X switches allows an unauthenticated remote attacker to bypass configured egress ACLs. The issue stems from traffic flooding from unlearned MAC addresses when a VLAN's MAC address table is flushed (either manually triggered or due to table overflow). This traffic bypasses the SVI's egress ACL because the switch floods unicast traffic from unknown MACs instead of applying ACL filtering.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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 device modelRun 'show version' or 'show inventory' to confirm the hardware is a Catalyst 9500X or 9600X switchAffected if Device is a Catalyst 9500X or 9600X series switch
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Check IOS XE versionRun 'show version' and locate the IOS XE software version stringAffected if IOS XE version is in the affected range (compare your installed version to the affected ranges)
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Verify SVI egress ACL configurationRun 'show ip interface [vlan-id]' for each SVI and check for outbound access-list references in the outputAffected if Egress ACLs are applied to SVI interfaces using 'ip access-group [name] out'
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Detect MAC address table flush eventsRun 'show mac address-table count' and 'show mac address-table aging-time'; monitor logs for 'MAC address table' and 'flush' keywordsAffected if MAC address table flushes have occurred or the table is frequently aging out entries
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Check for unknown unicast floodingRun 'show mac address-table unicast' and 'show interface | include Unknown unicast' to identify if unknown unicast traffic is being floodedAffected if Unknown MAC addresses are being flooded without ACL filtering applied
You are affected if you run Cisco IOS XE on Catalyst 9500X/9600X switches with egress ACLs configured on SVIs, and MAC address table flush events cause unknown unicast traffic to bypass those ACLs.
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 dataApply the Cisco software update/patch when available. In the interim, implement network segmentation to restrict access to VLANs with sensitive resources, and monitor for MAC address table flush events that could indicate exploitation attempts.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 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 $5,600.
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Free · runs locallyCheck whether your project pulls in CVE-2025-20316 — 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-2025-20316 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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