CVE-2023-20067: Cisco IOS XE DoS Vulnerability

CVE-2023-20067 Overview

CVE-2023-20067 is a denial of service (DoS) vulnerability in the HTTP-based client profiling feature of Cisco IOS XE Software running on Wireless LAN Controllers (WLCs). An unauthenticated adjacent attacker can send crafted traffic through a wireless access point to trigger high CPU utilization on the controller. The condition prevents new wireless client associations from succeeding until the offending traffic stops. The vulnerability stems from insufficient input validation of received traffic and is tracked under CWE-770 (Allocation of Resources Without Limits or Throttling). Cisco published the issue on March 23, 2023.

Critical Impact
An adjacent unauthenticated attacker can exhaust controller CPU resources, disrupting wireless client onboarding across all access points served by the affected WLC.

Affected Products

Cisco IOS XE Software 16.10.x and 16.11.x releases on Wireless LAN Controllers
Cisco IOS XE Software 16.12.x and 17.1.x through 17.3.x releases on WLCs
Cisco IOS XE Software 17.4.x through 17.9.1 with HTTP-based client profiling enabled

Discovery Timeline

2023-03-23 - CVE-2023-20067 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-20067

Vulnerability Analysis

The vulnerability resides in the HTTP-based client profiling subsystem of Cisco IOS XE on Wireless LAN Controllers. WLCs use HTTP client profiling to classify devices joining the wireless network by inspecting user-agent strings and other HTTP metadata. The code path that parses this client-supplied traffic does not adequately validate input before processing. Crafted traffic forwarded by an access point causes disproportionate CPU consumption on the controller. As CPU saturates, the controller is unable to service new association requests from legitimate wireless clients. Existing sessions may remain operational, but onboarding stalls until the malicious traffic ceases. Cisco confirms the system returns to a normal operational state automatically once the offending traffic stops.

Root Cause

The root cause is insufficient input validation combined with unbounded resource consumption ([CWE-770]) in the HTTP profiling parser. Because the profiler runs without enforcing throttling or sanity limits on parsed fields, malformed or oversized input drives CPU utilization beyond sustainable thresholds. The flaw is logic-level rather than memory-corruption based, so no code execution or data disclosure occurs.

Attack Vector

Exploitation requires adjacent network access, meaning the attacker must be within wireless range of an access point associated with a vulnerable WLC. Authentication is not required. The attacker sends crafted HTTP traffic through the access point toward the controller. Because the attack vector is wireless adjacency rather than the broader Internet, exposure is limited to attackers physically near corporate Wi-Fi coverage. The vulnerability affects availability only — confidentiality and integrity remain intact. Refer to the Cisco Security Advisory cisco-sa-ewlc-dos-wFujBHKw for protocol-level details.

Detection Methods for CVE-2023-20067

Indicators of Compromise

Sustained high CPU utilization on Cisco WLC processes responsible for HTTP client profiling, without a corresponding increase in legitimate client load.
Surge in failed wireless client association attempts coinciding with the CPU spike.
Unusual or malformed HTTP traffic patterns originating from clients associated with one or more access points.

Detection Strategies

Monitor show processes cpu and show platform resources output on Cisco IOS XE WLCs for abnormal CPU consumption tied to HTTP profiling tasks.
Correlate WLC syslog events indicating association failures with wireless intrusion detection alerts from access points reporting anomalous client behavior.
Capture and inspect HTTP traffic at the controller to identify crafted user-agent fields or oversized headers consistent with profiling abuse.

Monitoring Recommendations

Forward WLC syslog and SNMP CPU telemetry to a centralized SIEM and alert on sustained CPU thresholds above baseline.
Track wireless association success and failure rates per access point and trigger investigations when failures spike without infrastructure changes.
Enable wireless intrusion prevention (wIPS) policies that flag clients generating malformed HTTP profiling traffic.

How to Mitigate CVE-2023-20067

Immediate Actions Required

Identify all Cisco IOS XE WLCs running affected releases and prioritize them for the fixed software train listed in the Cisco advisory.
If patching is not immediately possible, evaluate whether HTTP-based client profiling is required for business operations.
Restrict physical and wireless proximity controls, since exploitation requires adjacent network access.

Patch Information

Cisco has released fixed software versions addressing this issue. Customers should consult the Cisco Security Advisory cisco-sa-ewlc-dos-wFujBHKw for the specific fixed release matching their deployed train and upgrade through standard Cisco IOS XE upgrade procedures.

Workarounds

Disable HTTP-based client profiling on the WLC if device classification by HTTP metadata is not required. DHCP- or RADIUS-based profiling can serve as alternatives.
Apply wireless segmentation and pre-authentication ACLs to limit the traffic that reaches the controller from unauthenticated clients.
Use wireless intrusion prevention features to detect and contain rogue clients producing malformed HTTP traffic.

bash

# Configuration example — disable HTTP-based client profiling on a Cisco IOS XE WLC
# Consult the Cisco advisory for the exact command set matching your release
configure terminal
 no device-classifier
 wireless profile policy default-policy-profile
  no http-tlv-caching
 end
write memory