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CVE-2021-1268

7.4 HIGH
Denial of Service

📋 TL;DR

This vulnerability in Cisco IOS XR Software allows an unauthenticated attacker on the same network segment as management interfaces to cause IPv6 flooding by sending specially crafted IPv6 packets. This can lead to network degradation or denial of service conditions. Only devices with IPv6-enabled management interfaces running affected Cisco IOS XR Software versions are vulnerable.

💻 Affected Systems

Products:
  • Cisco IOS XR Software
Versions: All releases prior to the fixed releases specified in the Cisco advisory
Operating Systems: Cisco IOS XR
Default Config Vulnerable: ⚠️ Yes
Notes: Only affects devices with IPv6 enabled on management interfaces. Management interfaces include GigabitEthernet, TenGigE, and other management ports.

📦 What is this software?

Ios Xr by Cisco

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Ios Xr by Cisco

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Ios Xr by Cisco

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Ios Xr by Cisco

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⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete network outage affecting all management interfaces on the segment, potentially disrupting management of critical network infrastructure and causing cascading failures.

🟠

Likely Case

Network performance degradation on management network segments, intermittent management access issues, and potential service disruptions.

🟢

If Mitigated

Minimal impact if management interfaces are isolated, IPv6 is disabled, or proper network segmentation is implemented.

🌐 Internet-Facing: LOW - Management interfaces should not be internet-facing, and exploitation requires adjacency to the management network.
🏢 Internal Only: HIGH - Attackers with internal network access adjacent to management interfaces can exploit this without authentication.

🎯 Exploit Status

Public PoC: ✅ No
Weaponized: UNKNOWN
Unauthenticated Exploit: ⚠️ Yes
Complexity: LOW

Exploitation requires network adjacency to management interfaces and knowledge of IPv6 multicast addressing. No authentication required.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Refer to Cisco Security Advisory for specific fixed releases for each platform

Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xripv6-spJem78K

Restart Required: Yes

Instructions:

1. Review Cisco Security Advisory for your specific platform. 2. Download appropriate fixed software release. 3. Schedule maintenance window. 4. Backup configuration. 5. Install update following Cisco IOS XR upgrade procedures. 6. Verify functionality post-upgrade.

🔧 Temporary Workarounds

Disable IPv6 on Management Interfaces

cisco-ios-xr

Disable IPv6 protocol on all management interfaces to prevent exploitation

configure
interface GigabitEthernet0/0/0/0
no ipv6 enable
commit

Implement Network Segmentation

all

Isolate management interfaces on dedicated VLANs with strict access controls

🧯 If You Can't Patch

  • Implement strict network access controls to limit who can reach management interfaces
  • Deploy network monitoring to detect IPv6 flooding attempts and anomalous traffic patterns

🔍 How to Verify

Check if Vulnerable:

Check IOS XR version and verify if IPv6 is enabled on management interfaces using 'show ipv6 interface' command

Check Version:

show version | include Cisco IOS XR

Verify Fix Applied:

Verify upgraded to fixed release using 'show version' and confirm IPv6 flood protection is functioning

📡 Detection & Monitoring

Log Indicators:

  • High volume of IPv6 multicast traffic on management interfaces
  • Interface error counters increasing rapidly
  • System log messages about network congestion

Network Indicators:

  • Unusual IPv6 multicast traffic (FF01::1, FF02::1) on management network
  • Sudden increase in IPv6 packet rates
  • Network performance degradation on management segments

SIEM Query:

source_interface:management AND protocol:IPv6 AND (dst_ip:FF01::1 OR dst_ip:FF02::1) AND packet_rate > threshold

📊 Metadata

CVE ID: CVE-2021-1268
CVSS v3 Score: 7.4 (HIGH)
CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CWE: CWE-1076
Published: February 4, 2021
Last Updated: November 21, 2024

🔗 References

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