iOSOperating system · Cisco
CVE-2020-3479
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 implementation of Multiprotocol Border Gateway Protocol (MP-BGP) for the Layer 2 VPN (L2VPN) Ethernet VPN (EVPN) address family in Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. The vulnerability is due to incorrect processing of Border Gateway Protocol (BGP) update messages that contain crafted EVPN attributes. An attacker could exploit this vulnerability by sending BGP update messages with specific, malformed attributes to an affected device. A successful exploit could allow the attacker to cause an affected device to crash, 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 confidenceThis vulnerability exists in Cisco IOS and IOS XE Software's implementation of MP-BGP for L2VPN EVPN. An unauthenticated remote attacker can send specially crafted BGP update messages containing malformed EVPN attributes, causing the affected device to crash and result in a denial of service.
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
iOSOperating system
all versions
Ios XeOperating system
all versionsCVSS 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
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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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Identify the device OS and versionExecute 'show version' or 'show ios version' on the device CLI to confirm it is running Cisco IOS or Cisco IOS XEAffected if The device runs Cisco IOS or IOS XE (all versions are affected)
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Verify L2VPN EVPN feature is configuredCheck the running configuration for 'l2vpn' or 'evpn' configuration mode entries, or use 'show l2vpn evpn' command to see if EVPN is configuredAffected if L2VPN EVPN is configured and operational - the vulnerability only affects systems with this feature enabled
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Confirm MP-BGP is used for EVPNCheck BGP configuration for 'address-family l2vpn evpn' under the BGP routing process, or use 'show bgp l2vpn evpn summary' to verify BGP peering for EVPNAffected if MP-BGP for L2VPN EVPN address family is configured and active
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Assess BGP peer exposureReview 'show bgp neighbors' output to list all BGP peers, particularly external peers (e.g., in different AS) that could send untrusted update messagesAffected if The device has BGP peering with untrusted or external neighbors that could send specially crafted update messages
A device is affected if it runs Cisco IOS or IOS XE with L2VPN EVPN configured over MP-BGP and has exposure to untrusted BGP peers.
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 Cisco security updates when available. Until then, filter or restrict BGP peering to trusted neighbors only, and implement BGP route validation to reject malformed update messages.
Fix this in iOS
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-3479 — 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-2020-3479 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.
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- Version or environment caveats, and links to real fixes
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