CVE-2025-20202: Cisco IOS XE Wireless DoS Vulnerability

CVE-2025-20202 Overview

Cisco disclosed CVE-2025-20202, a denial of service (DoS) vulnerability affecting Cisco IOS XE Wireless Controller Software. The flaw resides in how the wireless controller processes Cisco Discovery Protocol (CDP) neighbor reports received from managed access points (APs). An unauthenticated, adjacent attacker can send a crafted CDP packet to an AP and trigger an unexpected reload of the upstream wireless controller. The reload disrupts wireless services for every client and AP managed by that controller. The vulnerability is tracked under [CWE-805] (Buffer Access with Incorrect Length Value) and Cisco has published a fixed software release.

Critical Impact
A single crafted CDP packet sent to an associated access point can crash and reload the Cisco IOS XE wireless controller, taking the entire managed wireless network offline.

Affected Products

Cisco IOS XE Wireless Controller Software (multiple 16.x releases, including 16.10.x, 16.11.x, and 16.12.x)
Cisco IOS XE Wireless Controller Software (17.x releases through 17.15.x)
Cisco Catalyst 9800 Series Wireless Controllers and embedded wireless controllers running affected IOS XE versions

Discovery Timeline

2025-05-07 - CVE-2025-20202 published to NVD
2025-07-08 - Last updated in NVD database

Technical Details for CVE-2025-20202

Vulnerability Analysis

The vulnerability stems from insufficient input validation in the code path that handles CDP neighbor reports sent from access points to their controlling wireless LAN controller (WLC). When an AP forwards CDP neighbor information collected from its local network segment, the controller parses the report and updates internal CDP tables. Improperly bounded length values during this parsing allow an attacker-controlled CDP packet to corrupt memory or trigger an exception. The result is an unrecoverable error that forces the controller to reload, breaking control-plane connectivity (CAPWAP) for every AP it manages. CWE-805 classification indicates the affected code accesses a buffer using an incorrect length value.

Root Cause

The underlying defect is improper validation of fields within CDP TLVs (Type-Length-Value structures) received from APs. The controller trusts length and offset values supplied in the AP-relayed CDP report without sufficient bounds checking, leading to out-of-bounds memory access during parsing.

Attack Vector

Exploitation requires adjacent network access. The attacker must be positioned on a Layer 2 segment reachable by a target access point so that the malicious CDP frame is received by the AP and relayed to the controller. No authentication or user interaction is required. The impact scope is changed because the crash occurs on the controller, not on the AP that initially received the packet. A successful exploit causes a full controller reload, producing a DoS condition that affects the wireless network until the controller recovers.

No verified public exploit code is available for this issue. See the Cisco Security Advisory for vendor-supplied technical details.

Detection Methods for CVE-2025-20202

Indicators of Compromise

Unexpected reloads of Cisco Catalyst 9800 or other IOS XE wireless controllers with crash files referencing CDP processing
Mass CAPWAP tunnel reestablishment events from APs following a controller reload
Anomalous or malformed CDP frames observed on wired segments where APs are connected

Detection Strategies

Inspect controller crashinfo and show logging output for tracebacks tied to CDP neighbor processing after an unscheduled reload
Monitor for CDP frames with abnormal TLV lengths or unusual source MAC addresses on AP-facing access ports
Correlate AP disassociation storms with controller availability metrics to identify potential DoS attempts

Monitoring Recommendations

Forward syslog and SNMP traps from wireless controllers to a central SIEM and alert on %PLATFORM- or process-crash events
Enable port security and storm-control on switch ports connecting access points to limit malicious L2 traffic
Baseline normal CDP neighbor counts per AP and alert on sudden spikes or malformed packet counters

How to Mitigate CVE-2025-20202

Immediate Actions Required

Identify all Cisco IOS XE wireless controllers and confirm their software versions against the Cisco advisory
Upgrade affected controllers to a fixed IOS XE release as listed in the Cisco Security Advisory
Restrict physical and logical access to switch ports that connect access points to prevent rogue CDP injection

Patch Information

Cisco has released fixed software addressing CVE-2025-20202. Customers should consult the Cisco Security Advisory cisco-sa-ewlc-cdp-dos-fpeks9K for the specific fixed releases that apply to their deployed train (16.12, 17.3, 17.6, 17.9, 17.12, 17.15, and later). There are no software workarounds that fully address the vulnerability.

Workarounds

Disable CDP on access point ethernet ports where operationally feasible to remove the attack surface
Enforce strict Layer 2 segmentation so that only trusted devices share the broadcast domain with managed APs
Apply switch-level controls such as private VLANs and BPDU/CDP filtering on edge ports facing untrusted clients

bash

# Example: disable CDP on a switch interface connected to an AP-adjacent untrusted device
interface GigabitEthernet1/0/24
 no cdp enable

# Verify running IOS XE version on the wireless controller
show version | include IOS XE