CVE-2021-1268

Cisco IOS XR Software IPv6 Flood Denial of Service Vulnerability

MEDIUM
6.5
CVSS Score
Published: February 4, 2021 at 04:35 PM UTC
Updated: June 17, 2026 at 03:31 AM UTC
3 products affected across 1 vendorIOS XrNcs 1002Ncs 1001

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Severity
MEDIUM6.5
Exploit prediction
EPSS 0.5%
SSVC
No known exploit

Description

A vulnerability in the IPv6 protocol handling of the management interfaces of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause an IPv6 flood on the management interface network of an affected device. The vulnerability exists because the software incorrectly forwards IPv6 packets that have an IPv6 node-local multicast group address destination and are received on the management interfaces. An attacker could exploit this vulnerability by connecting to the same network as the management interfaces and injecting IPv6 packets that have an IPv6 node-local multicast group address destination. A successful exploit could allow the attacker to cause an IPv6 flood on the corresponding network. Depending on the number of Cisco IOS XR Software nodes on that network segment, exploitation could cause excessive network traffic, resulting in network degradation or a denial of service (DoS) condition.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 6.7.37.1.0 ≤ v < 7.1.37.2.0 ≤ v < 7.2.27.3.0
Affected range stops below 6.7.3, so it looks safe — our inference, not a vendor statement
Affected range stops below 7.1.3, so it looks safe — our inference, not a vendor statement
Affected range stops below 7.2.2, so it looks safe — our inference, not a vendor statement
cisco-ncs-1001 (environment) · cisco-ncs-1002 (environment)
All versions
All versions

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
ADJACENT_NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-1076

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