CVE-2024-20271: Cisco IOS XE Denial of Service Vulnerability

CVE-2024-20271 Overview

A vulnerability in the IP packet processing of Cisco Access Point (AP) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation of certain IPv4 packets. An attacker could exploit this vulnerability by sending a crafted IPv4 packet either to or through an affected device. A successful exploit could allow the attacker to cause an affected device to reload unexpectedly, resulting in a DoS condition.

Notably, the attacker does not need to be associated with the affected AP to successfully exploit this vulnerability. This vulnerability cannot be exploited by sending IPv6 packets.

Critical Impact

Unauthenticated remote attackers can cause Cisco Access Points to unexpectedly reload, disrupting wireless network connectivity for all connected users and potentially impacting critical business operations.

Affected Products

• Cisco IOS XE
• Cisco Business Access Points (140AC, 141ACM, 142ACM, 143ACM, 145AC, 240AC)
• Cisco Business 150AX and 151AXM Access Points
• Cisco Wireless LAN Controller Software

Discovery Timeline

• 2024-03-27 - CVE CVE-2024-20271 published to NVD
• 2025-08-06 - Last updated in NVD database

Technical Details for CVE-2024-20271

Vulnerability Analysis

This Denial of Service vulnerability exists within the IPv4 packet processing functionality of Cisco Access Point Software. The vulnerability stems from improper input validation (CWE-20) when the access point processes certain IPv4 packets. When a malformed or specially crafted IPv4 packet reaches the vulnerable component, the access point fails to properly handle the unexpected input, leading to a system crash and subsequent device reload.

The impact is significant for enterprise environments as the vulnerability can be exploited remotely over the network without any authentication or user interaction. The attacker does not need to be associated with the target access point, meaning they can potentially exploit this vulnerability from any network position that can route packets to or through the affected device. The scope of the vulnerability is changed, meaning the impact extends beyond the vulnerable component itself to affect dependent resources—in this case, all wireless clients connected to the access point.

Root Cause

The root cause is insufficient input validation (CWE-20) of certain IPv4 packets within the Cisco Access Point Software. The packet processing routine does not adequately verify the structure, length, or content of incoming IPv4 packets before attempting to process them. This allows malformed packets to trigger unexpected behavior in the packet handler, ultimately causing the device to crash and reload.

Attack Vector

The attack can be executed remotely over the network without authentication. An attacker sends specially crafted IPv4 packets either directly to an affected access point or routes them through the device. The attack does not require the attacker to be associated with the wireless network managed by the target AP.

The attack characteristics include:

• Network-based delivery: Crafted packets can traverse standard network infrastructure
• No authentication required: Attackers need no credentials or prior access
• No user interaction: The exploit triggers automatically upon packet processing
• IPv4-only: The vulnerability specifically affects IPv4 packet handling; IPv6 packets cannot be used for exploitation

For detailed technical information about the vulnerability and exploitation scenarios, refer to the Cisco Security Advisory.

Detection Methods for CVE-2024-20271

Indicators of Compromise

• Unexpected access point reboots or restarts without scheduled maintenance
• Multiple access point crash events occurring in rapid succession across the network
• Anomalous IPv4 traffic patterns targeting access point management interfaces
• Syslog entries indicating unexpected device reloads or memory corruption events

Detection Strategies

• Monitor access point uptime metrics and alert on unexpected reboots or crash events
• Implement network traffic analysis to detect malformed IPv4 packets targeting access point IP addresses
• Configure SNMP traps to alert on AP reboot events and correlate with traffic logs
• Deploy intrusion detection systems with signatures for known DoS attack patterns against Cisco devices

Monitoring Recommendations

• Enable comprehensive logging on Cisco Wireless LAN Controllers to capture AP state changes
• Configure centralized syslog collection for all affected access points to correlate crash events
• Implement network flow monitoring to identify suspicious traffic patterns directed at AP infrastructure
• Establish baseline uptime metrics for access points to quickly identify anomalous behavior

How to Mitigate CVE-2024-20271

Immediate Actions Required

• Review the Cisco Security Advisory and identify all affected devices in your environment
• Prioritize patching of internet-facing or externally accessible access points
• Implement network segmentation to limit exposure of access point management interfaces
• Consider implementing access control lists (ACLs) to restrict traffic to access points from trusted sources

Patch Information

Cisco has released software updates that address this vulnerability. Customers are advised to consult the Cisco Security Advisory for specific fixed software versions applicable to their deployment. The advisory includes version information for Cisco IOS XE, Business Access Points, and Wireless LAN Controller Software.

Organizations should verify their current software versions using the Cisco Software Checker tool and plan upgrades according to their change management procedures.

Workarounds

• Implement infrastructure ACLs to filter potentially malicious IPv4 traffic before it reaches access points
• Consider network segmentation to isolate wireless infrastructure from untrusted network segments
• Deploy intrusion prevention systems (IPS) with updated signatures to detect and block exploitation attempts
• Monitor for Cisco PSIRT updates regarding additional mitigation options

# Example ACL configuration to restrict access to AP management
# Apply appropriate ACLs on upstream network devices
# Consult Cisco documentation for your specific platform

# Verify current AP software version
show version

# Check AP status and uptime
show ap summary

# Review recent system events for crash indicators
show logging