CVE-2024-20450: Cisco SPA 301 Firmware RCE Vulnerability

CVE-2024-20450 Overview

CVE-2024-20450 is a critical buffer overflow vulnerability affecting the web-based management interface of Cisco Small Business SPA300 Series and SPA500 Series IP Phones. This vulnerability allows an unauthenticated, remote attacker to execute arbitrary commands on the underlying operating system with root privileges. The flaw exists because incoming HTTP packets are not properly checked for errors, which can result in a buffer overflow condition when processing specially crafted HTTP requests.

Critical Impact

Unauthenticated remote attackers can achieve complete system compromise with root-level command execution on affected Cisco IP phones through crafted HTTP requests.

Affected Products

• Cisco SPA301 1-Line IP Phone (all firmware versions)
• Cisco SPA303 3-Line IP Phone (all firmware versions)
• Cisco SPA501G 8-Line IP Phone (all firmware versions)
• Cisco SPA502G 1-Line IP Phone (all firmware versions)
• Cisco SPA504G 4-Line IP Phone (all firmware versions)
• Cisco SPA508G 8-Line IP Phone (all firmware versions)
• Cisco SPA509G 12-Line IP Phone (all firmware versions)
• Cisco SPA512G 1-Line IP Phone (all firmware versions)
• Cisco SPA514G 4-Line IP Phone (all firmware versions)
• Cisco SPA525G 5-Line IP Phone (all firmware versions)
• Cisco SPA525G2 5-Line IP Phone (all firmware versions)

Discovery Timeline

• August 7, 2024 - CVE-2024-20450 published to NVD
• August 23, 2024 - Last updated in NVD database

Technical Details for CVE-2024-20450

Vulnerability Analysis

This vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The web-based management interface of the affected Cisco IP phones fails to properly validate the size of incoming HTTP packet data before copying it into fixed-size memory buffers. When an attacker sends a maliciously crafted HTTP request containing oversized data, the application writes beyond the allocated buffer boundaries, corrupting adjacent memory regions.

The vulnerability is particularly severe because it can be exploited without any authentication, meaning any attacker with network access to the device's web management interface can attempt exploitation. Successful exploitation results in arbitrary command execution with root privileges, giving attackers complete control over the affected device.

Root Cause

The root cause of CVE-2024-20450 lies in the inadequate input validation within the HTTP request processing routines of the affected firmware. Specifically, the web server component fails to perform proper bounds checking when handling HTTP packet data. This oversight allows attackers to overflow internal buffers by providing input that exceeds expected lengths. The lack of memory-safe programming practices in the firmware's HTTP handling code creates the conditions necessary for buffer overflow exploitation.

Attack Vector

The attack vector for this vulnerability is network-based, requiring the attacker to have access to the web management interface of the target device. The exploitation flow involves:

1. The attacker identifies a vulnerable Cisco SPA300 or SPA500 series IP phone with an accessible web management interface
2. The attacker crafts a malicious HTTP request containing specially formatted data designed to overflow internal buffers
3. The crafted request is sent to the target device's web interface
4. The vulnerable firmware processes the request without proper size validation
5. The oversized data overflows the internal buffer, potentially overwriting critical memory structures
6. The attacker achieves arbitrary command execution with root privileges on the underlying operating system

The vulnerability can be triggered by sending HTTP requests to the device. The malformed request causes the web server to write data beyond allocated buffer boundaries, enabling attackers to inject and execute arbitrary commands. For detailed technical information, refer to the Cisco Security Advisory.

Detection Methods for CVE-2024-20450

Indicators of Compromise

• Unexpected HTTP traffic to Cisco SPA IP phone web management interfaces from external or unauthorized sources
• Anomalous process execution or unexpected system commands running on IP phone devices
• Unusual network connections originating from IP phone devices to external hosts
• System instability, crashes, or unexpected reboots of affected IP phone devices

Detection Strategies

• Implement network monitoring to detect unusual HTTP request patterns targeting IP phone management interfaces
• Deploy intrusion detection/prevention systems (IDS/IPS) with signatures for buffer overflow attacks against Cisco devices
• Monitor for abnormally large HTTP requests directed at Cisco SPA IP phones
• Review access logs for the web management interface to identify suspicious access patterns

Monitoring Recommendations

• Enable logging on network firewalls and segmentation devices for traffic destined to IP phone management interfaces
• Configure SIEM alerts for HTTP requests exceeding normal size thresholds targeting Cisco IP phone subnets
• Establish baseline network behavior for IP phone devices and alert on deviations
• Monitor for any outbound connections from IP phones that deviate from expected VoIP traffic patterns

How to Mitigate CVE-2024-20450

Immediate Actions Required

• Restrict network access to the web management interface of affected Cisco SPA IP phones using firewall rules or VLANs
• Disable the web-based management interface if not operationally required
• Isolate affected devices on a dedicated management VLAN with strict access controls
• Implement network segmentation to limit exposure of IP phone management interfaces to trusted networks only

Patch Information

Cisco has released a security advisory addressing this vulnerability. Organizations should consult the Cisco Security Advisory for specific remediation guidance and firmware update availability. Note that SPA300 and SPA500 series IP phones have reached end-of-life status, and Cisco may not provide firmware updates. Organizations using these devices should evaluate migration to supported products.

Workarounds

• Disable the web-based management interface on affected devices if remote management is not required
• Implement access control lists (ACLs) to restrict HTTP access to the management interface to trusted IP addresses only
• Deploy network-based security controls such as web application firewalls to filter malicious HTTP requests
• Consider replacing end-of-life SPA300 and SPA500 series phones with currently supported Cisco IP phone models

# Example ACL configuration to restrict management access (Cisco IOS)
# Apply to the interface facing the IP phone network
access-list 101 permit tcp 192.168.10.0 0.0.0.255 host 192.168.20.100 eq 80
access-list 101 deny tcp any host 192.168.20.100 eq 80
access-list 101 permit ip any any