Ios XeOperating system · Cisco
CVE-2020-3359
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 multicast DNS (mDNS) feature of Cisco IOS XE Software for Cisco Catalyst 9800 Series Wireless Controllers could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. The vulnerability is due to improper validation of mDNS packets. An attacker could exploit this vulnerability by sending a crafted mDNS packet to an affected device. A successful exploit could cause a device to reload, resulting in a DoS condition.
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 vulnerability in the multicast DNS (mDNS) feature of Cisco IOS XE Software for Cisco Catalyst 9800 Series Wireless Controllers allows an unauthenticated, remote attacker to send a crafted mDNS packet with improper validation, causing the device to reload and result in a denial of service condition.
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
Ios XeOperating system
= 16.12.1CVSS 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
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
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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Confirm device is a Catalyst 9800 Series Wireless ControllerUse 'show version' command or check the device model via 'show inventory' to verify the hardware is a Cisco Catalyst 9800 Series Wireless ControllerAffected if Device model is NOT a Catalyst 9800 Series Wireless Controller (different models are not affected by this specific CVE)
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Identify the installed IOS XE versionExecute 'show version' on the device CLI and locate the version string (typically displayed as 'Version 16.x.x' or similar)Affected if Installed version is exactly 16.12.1 (note: the '=' indicates only this specific version is affected, not a range)
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Verify if mDNS feature is configuredRun 'show running-config | include mdns' or 'show mdns status' to check if multicast DNS is enabled on the deviceAffected if mDNS is not configured or enabled (if mDNS is disabled, the attacker cannot exploit this vulnerability)
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Check for mDNS service policy configurationUse 'show mdns service-policy' or 'show running-config | include mdns service-policy' to see if any mDNS service policies are definedAffected if No mDNS service policies exist (the vulnerability requires active mDNS processing to be exploited)
Device is affected only if it is a Catalyst 9800 Series Wireless Controller running IOS XE version 16.12.1 with mDNS feature enabled and configured.
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 patch for this vulnerability; if unavailable, consider disabling the mDNS feature if not required or implementing network-level filtering of mDNS traffic as a workaround.
Fix this in Ios Xe
Scoped from the published advisory
- Consultation3.0 h
- Implementation3.0 h
- Testing2.0 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 $2,880.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-3359 — 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-2020-3359 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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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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