CVE-2022-20821: Cisco IOS XR Open Port Vulnerability

CVE-2022-20821 is an open-port vulnerability in Cisco IOS XR software. When a health-check feature is activated, the software opens TCP port 6379 by default, exposing a Redis instance that runs inside the NOSi container. An unauthenticated attacker who can reach that port may connect to the Redis service. Because IOS XR is commonly used on service-provider and enterprise routing platforms, an exposed management or control-plane interface can give an attacker a foothold on critical network infrastructure. Confirm exact impact and fixed releases against the vendor advisory.

How it works

The weakness is classified as CWE-923 (improper restriction of communication channel to intended endpoints). In this case the health-check function starts a Redis instance inside the NOSi container and binds it to TCP 6379 without adequate access controls. Once the port is listening, any host that can reach the device on that port can open a connection to the Redis service. The CISA summary states that an attacker can thereby gain access to the Redis instance running within the container. No further exploit mechanics are provided in the public record; defenders should treat any reachable Redis endpoint on an IOS XR device as a potential unauthorized-access vector and verify details in Cisco’s advisory.

Am I affected? How to find it in your systems

Cisco IOS XR typically runs on carrier-grade and large-enterprise routers and related network elements. Inventory every device that reports an IOS XR image:

• Use configuration-management or network-discovery tools to list all IOS XR systems and their software versions.
• Check whether the health-check feature that activates the Redis instance is enabled; the vendor advisory will identify the precise feature name and default behavior.
• Scan management and control-plane interfaces for TCP port 6379. A listening socket on that port is a strong indicator that the vulnerable configuration is present.
• Review device logs and NetFlow/IPFIX records for unexpected inbound connections to port 6379, especially from non-management subnets. Successful Redis protocol handshakes or subsequent commands would be signs of exploitation, though specific log signatures are not detailed in the public summary.

Compare discovered versions and feature states against the fixed releases listed by Cisco; do not rely on version ranges stated elsewhere.

How to remediate

The required action is to apply the updates published by Cisco. Obtain the fixed software image from the vendor, validate its integrity, and schedule installation according to your change process. After the upgrade:

• Confirm that TCP 6379 is no longer open by default or is bound only to intended, restricted interfaces.
• Disable any unused health-check or container features that are not required for operations.
• Re-apply standard hardening: restrict management-plane access with control-plane policing or ACLs, enforce authentication on all remaining services, and ensure out-of-band management networks are isolated.

Document the change and re-scan to verify the port is closed or properly filtered.

If you can't patch immediately

Until the vendor update can be installed, reduce exposure with compensating controls:

• Block inbound TCP 6379 at network boundaries and on the device itself with interface ACLs or control-plane filters; allow the port only from explicitly authorized management hosts if the feature must remain active.
• Segment IOS XR devices onto dedicated management VRFs or out-of-band networks that are unreachable from general user or Internet segments.
• If a web application firewall or network IPS is in the path, apply a temporary signature or rule that drops Redis protocol traffic destined to the device (virtual patching).
• Increase monitoring: alert on any connection attempt to port 6379 and on anomalous container or process activity inside the NOSi environment.
• Disable the health-check feature that opens the port if operational requirements permit.

These steps do not replace the patch; they only lower risk until the official update is applied.

If your data may have been exposed

Actively exploited vulnerabilities can lead to unauthorized access and subsequent data exposure. While ransomware use of this CVE is not documented, any successful connection to the Redis instance should be treated as a potential compromise. Review device configurations, logs, and downstream systems for signs of lateral movement or data exfiltration. As a quick additional check, you can run a free exposure scan of your email addresses against known breach data sets to see whether associated credentials have appeared in prior incidents.