CVE-2024-0535 Overview
A critical stack-based buffer overflow vulnerability has been identified in Tenda PA6 firmware version 1.0.1.21. This vulnerability exists within the cgiPortMapAdd function located in the /portmap component of the httpd service. The flaw allows attackers to manipulate the groupName argument, leading to a stack-based buffer overflow condition that can be exploited remotely without authentication.
The exploit for this vulnerability has been publicly disclosed, significantly increasing the risk of active exploitation. The vendor (Tenda) was contacted regarding this security issue but did not provide any response, leaving affected devices potentially unpatched and vulnerable.
Critical Impact
This remotely exploitable buffer overflow vulnerability allows unauthenticated attackers to potentially achieve complete system compromise on affected Tenda PA6 devices, including arbitrary code execution with device-level privileges.
Affected Products
- Tenda PA6 Firmware version 1.0.1.21
- Tenda PA6 Hardware devices running vulnerable firmware
- Tendacn PA6 series routers
Discovery Timeline
- 2024-01-15 - CVE-2024-0535 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2024-0535
Vulnerability Analysis
This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when the cgiPortMapAdd function fails to properly validate the length of user-supplied input for the groupName parameter. The affected function resides in the httpd component, which handles HTTP requests to the /portmap endpoint on the device.
Stack-based buffer overflows are particularly dangerous in embedded devices like routers because they often lack modern memory protection mechanisms such as Address Space Layout Randomization (ASLR) or stack canaries. This makes exploitation more reliable and increases the likelihood of successful arbitrary code execution.
The network-accessible nature of this vulnerability means any attacker who can reach the device's web interface can attempt exploitation without requiring any prior authentication or user interaction.
Root Cause
The root cause of this vulnerability is improper input validation within the cgiPortMapAdd function. When processing HTTP requests to the /portmap endpoint, the function copies the user-supplied groupName parameter into a fixed-size stack buffer without properly checking the input length against the allocated buffer size. This allows an attacker to provide an overly long groupName value that exceeds the buffer boundaries, overwriting adjacent stack memory including the return address.
Attack Vector
The attack is network-based and can be launched remotely against any Tenda PA6 device exposing its web management interface. An attacker crafts a malicious HTTP request to the /portmap endpoint containing an oversized groupName parameter. When the cgiPortMapAdd function processes this request, the buffer overflow occurs, potentially allowing the attacker to hijack program execution.
Successful exploitation could enable an attacker to execute arbitrary code with the privileges of the httpd process, typically root on embedded devices. This could lead to complete device compromise, including the ability to modify device configuration, intercept network traffic, or use the device as a pivot point for further attacks within the network.
The vulnerability does not require authentication, and since the exploit has been publicly disclosed via the GitHub PoC Repository, the barrier to exploitation is significantly lowered.
Detection Methods for CVE-2024-0535
Indicators of Compromise
- Unusual or malformed HTTP requests to the /portmap endpoint on Tenda PA6 devices
- HTTP requests containing abnormally long groupName parameter values
- Unexpected crashes or restarts of the httpd service on affected devices
- Suspicious network connections originating from the Tenda PA6 device
Detection Strategies
- Implement network intrusion detection rules to identify HTTP requests with oversized parameters targeting the /portmap endpoint
- Monitor for anomalous traffic patterns to and from Tenda PA6 device management interfaces
- Deploy deep packet inspection to detect exploitation attempts containing buffer overflow payloads
- Audit device logs for httpd crashes or segmentation faults that may indicate exploitation attempts
Monitoring Recommendations
- Restrict access to the device web management interface to trusted administrative networks only
- Implement logging for all HTTP requests to the management interface
- Set up alerts for any access to the /portmap endpoint from non-administrative sources
- Monitor device behavior for signs of compromise such as unexpected configuration changes or outbound connections
How to Mitigate CVE-2024-0535
Immediate Actions Required
- Disable remote access to the Tenda PA6 web management interface if not required
- Place affected devices behind a firewall and restrict access to the management interface to trusted IP addresses only
- Monitor devices for signs of compromise and consider replacing devices with models from vendors with active security response programs
- Segment network to isolate IoT and network devices from critical systems
Patch Information
No vendor patch is currently available. The vendor (Tenda) was contacted about this vulnerability but did not respond. Users should implement workarounds and consider replacing affected devices with alternatives from vendors who provide timely security updates.
Additional technical information is available through the following resources:
Workarounds
- Disable the web management interface entirely if device administration is not required
- Use network ACLs or firewall rules to restrict access to the management interface (port 80/443) from untrusted networks
- Implement a VPN requirement for any remote device management needs
- Consider replacing the device with a model from a vendor with active security support and patch management
# Example firewall rules to restrict access to Tenda PA6 management interface
# Block external access to web management ports
iptables -A FORWARD -d <PA6_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <PA6_IP> -p tcp --dport 443 -j DROP
# Allow only trusted admin network
iptables -A FORWARD -s <ADMIN_NETWORK> -d <PA6_IP> -p tcp --dport 80 -j ACCEPT
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
