Security readout for executives and security teams
Plain-English summary
This flaw can let malformed BGP EVPN routing updates crash the BGP process on affected Cisco IOS XR devices. The business impact is network disruption, not data theft. Exposure is narrower than ordinary internet-facing bugs because the update must come from a configured BGP peer or be injected into an existing valid peer connection.
Executive priority
Treat as high priority for networks using Cisco IOS XR with BGP EVPN, especially service provider, data center, or critical routing environments. The main risk is availability loss from routing process restarts, with exposure dependent on peer trust boundaries.
Technical view
CVE-2019-16021 covers Cisco IOS XR BGP EVPN processing flaws caused by incorrect handling of crafted EVPN attributes in BGP update messages. Successful exploitation can restart the BGP process and cause denial of service. CVSS 3.0 is 8.6 with network attack vector, low complexity, no privileges, no user interaction, changed scope, and high availability impact.
Likely exposure
Likely exposed assets are Cisco IOS XR systems running BGP EVPN functionality. The source bundle does not identify specific affected versions beyond n/a, so version exposure must be confirmed against Cisco's advisory and local device inventory.
Exploitation context
The bundle does not show CISA KEV listing or active exploitation evidence. Exploitation requires a configured valid BGP peer or injection into an existing valid TCP connection to a BGP peer, which limits opportunistic internet exploitation but remains serious in provider and routed enterprise networks.
Researcher notes
Evidence identifies malformed EVPN attributes in BGP update messages as the trigger and BGP process restart as the impact. The affected version data in the bundle is incomplete. Avoid assuming broader product impact, public exploitation, or specific fixed releases without consulting Cisco's advisory.
Mitigation direction
- Inventory Cisco IOS XR routers and confirm whether BGP EVPN is enabled.
- Review Cisco's advisory for fixed software and vendor-approved workaround guidance.
- Limit BGP sessions to explicitly trusted peers and enforce existing peer-authentication controls.
- Monitor and alert on unexpected BGP process restarts or EVPN update anomalies.
- Coordinate remediation windows for routing infrastructure to avoid avoidable network disruption.
Validation and detection
- Map IOS XR devices running BGP EVPN against the Cisco advisory scope.
- Confirm all BGP EVPN peers are expected, documented, and operationally trusted.
- Review logs for unexpected BGP process restarts around EVPN update handling.
- Check routing telemetry for session resets, convergence events, or recurring EVPN instability.
- Verify remediation status from vendor guidance and configuration records.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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Open ATT&CK lookupCVE-2019-16021 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 8.6 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
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.
CVSS vector scores
1 official scoreWe 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.
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
8.6HighVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20200122 Cisco IOS XR Software BGP EVPN Denial of Service VulnerabilitiesCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Resource Management Errors
Resource Management Errors represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.