dbcve.org
Ios XrOperating system · Cisco

CVE-2019-16021

HIGH · 7.5 CVSS v3.1 Published 2020-09-23
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
Multiple vulnerabilities in the implementation of Border Gateway Protocol (BGP) Ethernet VPN (EVPN) functionality in Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. The vulnerabilities are due to incorrect processing of BGP update messages that contain crafted EVPN attributes. An attacker could exploit these vulnerabilities by sending BGP EVPN update messages with malformed attributes to be processed by an affected system. A successful exploit could allow the attacker to cause the BGP process to restart unexpectedly, resulting in a DoS condition. The Cisco implementation of BGP accepts incoming BGP traffic only from explicitly defined peers. To exploit these vulnerabilities, the malicious BGP update message would need to come from a configured, valid BGP peer, or would need to be injected by the attacker into the victim's BGP network on an existing, valid TCP connection to a BGP peer.

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 confidence

Vulnerabilities in Cisco IOS XR BGP EVPN implementation allow remote attackers to cause denial of service by sending malformed BGP update messages with crafted EVPN attributes, triggering unexpected BGP process restarts. The attacker must inject malicious BGP EVPN messages via a configured valid BGP peer or by hijacking an existing TCP connection to a BGP peer.

MitigationApply Cisco IOS XR software patches addressing CVE-2019-16021 and implement BGP MD5 authentication between peers to prevent unauthorized BGP session hijacking.

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 XrOperating system
Affected:= 6.6.1= 6.6.2= 6.6.25= 7.0.1

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
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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify the IOS XR version
    Run the command 'show version' on the Cisco IOS XR device and locate the software version string (typically labeled 'IOS XR' or 'Version').
    Affected if The installed version matches exactly 6.6.1, 6.6.2, 6.6.25, or 7.0.1.
  2. Confirm BGP is configured
    Run the command 'show running-config | include router bgp' or 'show bgp summary' to check if BGP is enabled on the device.
    Affected if BGP routing process is configured and active.
  3. Check if EVPN address family is enabled under BGP
    Run the command 'show running-config | include evpn' or inspect the BGP configuration for 'address-family l2vpn evpn' under the BGP router context.
    Affected if EVPN address family is configured under BGP (address-family l2vpn evpn).
  4. Verify if BGP peers are configured
    Run the command 'show bgp neighbor' or 'show running-config | include neighbor' to list configured BGP peers.
    Affected if BGP peers exist in the configuration, as the attack requires a valid peer or hijacked TCP connection to deliver malformed EVPN attributes.

The device is affected if it runs Cisco IOS XR version 6.6.1, 6.6.2, 6.6.25, or 7.0.1 AND has BGP with EVPN address family configured and active peers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco IOS XR software patches addressing CVE-2019-16021 and implement BGP MD5 authentication between peers to prevent unauthorized BGP session hijacking.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing12.0 h
  • Review / QA4.0 h
40.0 hours of engineering $7,000
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2019-16021 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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  • No spam, self-promotion, credentials, or personal data