CVE-2025-20140: Cisco IOS XE DoS Vulnerability

CVE-2025-20140 Overview

CVE-2025-20140 is a denial of service vulnerability in the Wireless Network Control daemon (wncd) of Cisco IOS XE Software for Wireless LAN Controllers (WLCs). An unauthenticated, adjacent wireless attacker can exhaust memory on an affected device by sending a series of IPv6 network requests from an associated wireless client. The flaw stems from improper memory management within the wncd process. Successful exploitation forces the controller to stop responding, disrupting wireless services across associated access points. The vulnerability is tracked under [CWE-789: Memory Allocation with Excessive Size Value].

Critical Impact
A successful exploit causes the wncd process to consume available memory and the device to stop responding, producing a denial of service condition that disrupts wireless connectivity for all clients managed by the controller.

Affected Products

Cisco IOS XE Software for Wireless LAN Controllers (multiple 16.x and 17.x trains through 17.14.1a)
Cisco Catalyst 9800-40, 9800-80, 9800-L, and 9800-CL Wireless Controllers for Cloud
Cisco Catalyst CW9800H1, CW9800H2, CW9800M and Catalyst 9105/9115/9117/9120/9130 series access points

Discovery Timeline

2025-05-07 - CVE-2025-20140 published to NVD
2025-07-31 - Last updated in NVD database

Technical Details for CVE-2025-20140

Vulnerability Analysis

The vulnerability resides in the Wireless Network Control daemon (wncd), the IOS XE process that manages wireless client state on Catalyst 9800 series controllers. The daemon allocates memory to track IPv6 network requests originating from associated wireless clients. Because the allocation paths do not properly bound the request volume or reclaim memory tied to abnormal client traffic, an attacker can drive wncd into a memory exhaustion state. Once available memory is consumed, the controller stops processing legitimate wireless events and becomes unresponsive.

Root Cause

The root cause is improper memory management within wncd when handling IPv6 traffic from associated wireless clients. The process allocates resources for incoming requests without enforcing limits or releasing memory under attack conditions, classified as [CWE-789].

Attack Vector

Exploitation requires adjacent network access. The attacker must associate as an IPv6 wireless client to the affected device. On open networks, association is unrestricted. On secured networks, the attacker must first authenticate. Once associated, the attacker transmits a series of IPv6 network requests toward the controller. The volume and pattern of requests force wncd to grow its memory footprint until the device exhausts available memory and stops responding. No user interaction on the controller side is required.

// No verified public exploit code is available for CVE-2025-20140.
// See the Cisco Security Advisory for technical details and fixed releases.

Detection Methods for CVE-2025-20140

Indicators of Compromise

Sustained growth in wncd process memory consumption visible through show processes memory platform sorted on the WLC.
Wireless client disconnects, association failures, or unresponsive management plane on Catalyst 9800 controllers.
Crash dumps or tracebacks referencing the wncd process following bursts of IPv6 client traffic.

Detection Strategies

Baseline wncd memory usage during normal operation and alert on deviations that exceed the baseline by a defined threshold.
Inspect IPv6 traffic patterns from individual wireless clients for anomalous request rates or repeated neighbor discovery and ICMPv6 floods.
Correlate WLC syslog and SNMP traps reporting memory pressure with recent client association events on open or guest SSIDs.

Monitoring Recommendations

Forward WLC syslog, SNMP, and process memory metrics to a centralized analytics platform for trend analysis and alerting.
Monitor authentication and association logs on guest and open SSIDs for clients generating disproportionate IPv6 traffic volumes.
Track availability metrics and management-plane reachability for Catalyst 9800 controllers to identify early signs of resource exhaustion.

How to Mitigate CVE-2025-20140

Immediate Actions Required

Apply the fixed Cisco IOS XE release identified in the Cisco Security Advisory cisco-sa-wlc-wncd-p6Gvt6HL to all Catalyst 9800 controllers.
Inventory wireless controllers and access points against the affected product list and prioritize controllers serving open or guest SSIDs.
Restrict and monitor association on open networks where unauthenticated clients can directly interact with the controller.

Patch Information

Cisco has published guidance and fixed software releases in the security advisory cisco-sa-wlc-wncd-p6Gvt6HL. Administrators should consult the advisory for the specific first-fixed releases that apply to each affected IOS XE train and upgrade accordingly.

Workarounds

Disable IPv6 on wireless client VLANs where IPv6 is not required, removing the attack surface used by this vulnerability.
Apply client rate limiting and per-client policies on the WLC to constrain abnormal traffic volumes from individual associated clients.
Require WPA2/WPA3-Enterprise authentication on production SSIDs and isolate guest or open SSIDs on a separate controller or VLAN.

bash

# Example: disable IPv6 on a wireless client VLAN interface (verify in a lab before deployment)
configure terminal
interface Vlan<client-vlan-id>
 no ipv6 address
 no ipv6 enable
end
write memory