CVE-2024-2815: Tenda AC15 Buffer Overflow Vulnerability

CVE-2024-2815 Overview

A critical stack-based buffer overflow vulnerability has been identified in Tenda AC15 router firmware version 15.03.20_multi. The vulnerability exists in the R7WebsSecurityHandler function within the /goform/execCommand endpoint, specifically in the Cookie Handler component. An attacker can exploit this vulnerability by manipulating the password argument, leading to a stack-based buffer overflow condition that can be triggered remotely without authentication.

Critical Impact

This vulnerability allows remote attackers to execute arbitrary code on affected Tenda AC15 routers without authentication, potentially leading to complete device compromise, network infiltration, and use of the device in botnet operations.

Affected Products

• Tenda AC15 Firmware version 15.03.05.20_multi
• Tenda AC15 Hardware
• Tenda AC15 Firmware (all variants of 15.03.20_multi)

Discovery Timeline

• 2024-03-22 - CVE-2024-2815 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2815

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when user-supplied data exceeds the allocated buffer space on the program stack. The affected function R7WebsSecurityHandler fails to properly validate the length of the password parameter received through the Cookie Handler before copying it to a fixed-size stack buffer.

The vulnerability is particularly dangerous because it can be exploited remotely through the network interface without requiring any authentication or user interaction. The complete lack of input validation on the password field allows attackers to overflow the stack buffer, potentially overwriting the function's return address and gaining control of program execution flow.

Root Cause

The root cause of this vulnerability lies in the improper bounds checking within the R7WebsSecurityHandler function when processing the password cookie parameter. The function allocates a fixed-size buffer on the stack to store the password value but does not verify that the incoming data fits within the allocated space. When an oversized password value is submitted, the excess data overflows into adjacent stack memory, corrupting critical control data structures including saved registers and return addresses.

This is a classic example of unsafe string handling in embedded device firmware, where performance optimizations often lead developers to skip essential input validation routines.

Attack Vector

The attack can be executed remotely via the network interface. An attacker can craft a malicious HTTP request to the /goform/execCommand endpoint with a specially crafted Cookie header containing an oversized password parameter. The attack requires no prior authentication and no user interaction, making it trivially exploitable by any network-adjacent attacker or, if the router's web interface is exposed to the internet, by remote attackers worldwide.

The exploitation sequence involves:

1. Sending an HTTP request to the /goform/execCommand endpoint
2. Including a Cookie header with an oversized password value
3. The R7WebsSecurityHandler function processes the cookie and copies the password to a stack buffer
4. The buffer overflow corrupts the stack, allowing the attacker to redirect execution

For detailed technical analysis of the vulnerability mechanism, refer to the GitHub Vulnerability Documentation and the VulDB advisory.

Detection Methods for CVE-2024-2815

Indicators of Compromise

• Unusual HTTP requests to /goform/execCommand with abnormally large Cookie headers
• Unexpected router reboots or firmware modifications
• Suspicious outbound network connections from the router to unknown external IP addresses
• Presence of unknown processes or services running on the device

Detection Strategies

• Monitor network traffic for HTTP requests to the /goform/execCommand endpoint containing oversized cookie values
• Implement web application firewall (WAF) rules to detect and block requests with abnormally large Cookie headers targeting Tenda devices
• Deploy intrusion detection signatures that identify buffer overflow attack patterns against embedded device web interfaces
• Conduct regular firmware integrity checks to detect unauthorized modifications

Monitoring Recommendations

• Enable comprehensive logging on network perimeter devices to capture traffic to and from IoT devices
• Implement network segmentation to isolate IoT devices like routers from critical network assets
• Monitor for abnormal device behavior including unexpected configuration changes or performance degradation
• Deploy SentinelOne Singularity Platform for comprehensive endpoint and network visibility to detect exploitation attempts

How to Mitigate CVE-2024-2815

Immediate Actions Required

• Isolate affected Tenda AC15 routers from untrusted networks immediately
• Disable remote administration and web management interfaces if not strictly required
• Implement network-level access controls to restrict access to the router's management interface
• Consider replacing affected devices with alternatives from vendors with responsive security practices

Patch Information

At the time of disclosure, the vendor (Tenda) was contacted but did not respond. No official patch has been released for this vulnerability. Organizations should monitor Tenda's official channels for any future firmware updates addressing this issue. Given the vendor's lack of response, users should strongly consider alternative mitigation strategies or device replacement.

For additional technical details, see the VulDB CTI entry.

Workarounds

• Restrict network access to the router's web management interface using firewall rules
• Place the router behind a network firewall that can filter malicious HTTP requests
• Disable the web administration interface entirely if management can be performed through alternative means
• Implement strict network segmentation to limit the potential impact of device compromise

# Example: Block external access to router management interface using iptables
# Run on a gateway/firewall device protecting the network

# Block external access to Tenda router web interface (port 80/443)
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP

# Allow only trusted management hosts
iptables -I FORWARD -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT