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CVE Record

CVE-2020-3479: Cisco IOS and IOS XE Software MP-BGP EVPN Denial of Service Vulnerability

A 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.

MediumCVSS 6.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2020-3479 can let a remote, unauthenticated attacker crash affected Cisco IOS or IOS XE devices by sending malformed BGP EVPN update messages. The business impact is service interruption, not data theft. Urgency depends on whether the organization runs MP-BGP EVPN on affected Cisco software in production paths.

Executive priority

Treat this as a moderate infrastructure availability risk. Prioritize it where EVPN/BGP devices support critical network paths, data centers, or tenant connectivity. It is less urgent for environments without affected Cisco IOS/IOS XE EVPN deployments.

Technical view

The flaw is incorrect input processing in MP-BGP for the L2VPN EVPN address family. Crafted BGP update messages with malformed EVPN attributes can trigger a device crash and denial of service. The source bundle lists CWE-20, CVSS 3.1 score 6.1, and affected Cisco IOS/IOS XE software context.

Likely exposure

Exposure is most likely on Cisco IOS or IOS XE devices running MP-BGP with the L2VPN EVPN address family enabled. The bundle specifically lists Cisco IOS 15.2(5)E1 and the Cisco advisory for IOS and IOS XE. Evidence does not support broader product claims.

Exploitation context

The bundle describes remote unauthenticated exploitation through crafted BGP update messages. It does not cite public exploitation, weaponized exploit availability, or CISA KEV listing. Because KEV is false, active exploitation should not be assumed from the provided evidence.

Researcher notes

The supplied evidence is limited to description, CVSS, CWE-20, one listed affected version entry, and Cisco advisory references. No exploit procedure, packet details, public exploitation evidence, or explicit fix details are included in the bundle.

Mitigation direction

  • Review the Cisco advisory for affected releases, fixed software, and official workarounds.
  • Inventory Cisco IOS and IOS XE devices that run MP-BGP EVPN.
  • Prioritize remediation for EVPN routers whose crash would disrupt production connectivity.
  • Apply only vendor-approved upgrades or mitigations confirmed in Cisco guidance.

Validation and detection

  • Confirm whether MP-BGP L2VPN EVPN is enabled on Cisco IOS or IOS XE devices.
  • Compare device software releases against Cisco advisory affected-release guidance.
  • Review device crash logs and BGP events for unexplained EVPN-related instability.
  • Verify remediation status after any vendor-approved upgrade or workaround.
Prepared
Confidence
medium
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-20: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2020-3479 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
6.1CVSS 3.1MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:N/A:H1.64Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.1Medium
CVSS 3.1 vector shape for CVE-2020-3479Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
CiscoCisco IOS 15.2(5)E1n/aListed
Weakness

CWE details

CWE-20

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.