CVE-2026-2876 Overview
A stack-based buffer overflow vulnerability has been identified in Tenda A18 firmware version 15.13.07.13. The vulnerability exists in the parse_macfilter_rule function within the /goform/setBlackRule endpoint, where improper handling of the deviceList argument allows remote attackers to trigger a buffer overflow condition. This firmware vulnerability affects network router devices and can be exploited remotely by authenticated attackers to potentially achieve code execution or cause denial of service.
Critical Impact
Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code or crash affected Tenda A18 router devices, compromising network security and availability.
Affected Products
- Tenda A18 Firmware version 15.13.07.13
- Tenda A18 Hardware Device
Discovery Timeline
- 2026-02-21 - CVE-2026-2876 published to NVD
- 2026-02-23 - Last updated in NVD database
Technical Details for CVE-2026-2876
Vulnerability Analysis
This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), specifically manifesting as a stack-based buffer overflow. The root cause lies in the parse_macfilter_rule function's failure to properly validate the length of user-supplied input through the deviceList parameter before copying it to a fixed-size stack buffer.
When processing requests to the /goform/setBlackRule endpoint, the firmware does not implement adequate bounds checking on the incoming deviceList argument. An attacker who can reach this endpoint over the network can craft a malicious request with an oversized deviceList value, causing data to overflow beyond the allocated stack buffer boundaries.
The exploit has been publicly disclosed according to available references, increasing the risk profile for unpatched devices. The network-accessible nature of this vulnerability means that any Tenda A18 device with the affected firmware version exposed to untrusted networks is potentially at risk.
Root Cause
The vulnerability stems from insufficient input validation in the parse_macfilter_rule function. The code fails to verify that the length of the deviceList parameter does not exceed the size of the destination buffer allocated on the stack. This is a classic memory corruption vulnerability pattern commonly found in embedded device firmware where memory-safe programming practices may not be consistently applied.
Attack Vector
The attack is network-based and requires low-privileged access to the device's web management interface. An attacker can exploit this vulnerability by sending a specially crafted HTTP request to the /goform/setBlackRule endpoint with a malicious deviceList parameter value. The oversized input overwrites adjacent stack memory, potentially corrupting return addresses or other critical data structures.
The vulnerability mechanism involves sending an HTTP POST request to the /goform/setBlackRule endpoint with a deviceList parameter containing data that exceeds expected buffer boundaries. When the parse_macfilter_rule function processes this input without proper length validation, the stack buffer overflow occurs. For detailed technical analysis, refer to the GitHub CVE Issue Discussion and VulDB entry #347114.
Detection Methods for CVE-2026-2876
Indicators of Compromise
- Unusual or malformed HTTP POST requests to /goform/setBlackRule with abnormally large deviceList parameter values
- Router device crashes, reboots, or unresponsive behavior following web management interface access
- Network logs showing repeated requests to the vulnerable endpoint from suspicious IP addresses
Detection Strategies
- Implement network intrusion detection rules to identify HTTP requests to /goform/setBlackRule with oversized POST body content
- Monitor for anomalous traffic patterns targeting Tenda A18 router management interfaces
- Deploy web application firewall rules to inspect and block requests with excessive parameter lengths to vulnerable endpoints
Monitoring Recommendations
- Enable logging on network perimeter devices to capture traffic destined for router management interfaces
- Regularly review device stability and uptime metrics for signs of exploitation attempts
- Configure alerts for repeated authentication attempts or unusual access patterns to router administration endpoints
How to Mitigate CVE-2026-2876
Immediate Actions Required
- Restrict access to the Tenda A18 web management interface to trusted internal networks only
- Implement network segmentation to prevent untrusted devices from reaching router administration endpoints
- Monitor the Tenda Official Website for firmware updates addressing this vulnerability
- Consider disabling remote management capabilities if not required
Patch Information
At the time of this publication, no vendor patch has been confirmed for this vulnerability. Organizations should monitor Tenda's official security advisories and support channels for firmware updates. The vulnerability affects firmware version 15.13.07.13, and users should apply any security updates as soon as they become available.
Additional technical details can be found at:
Workarounds
- Configure firewall rules to block external access to TCP ports used by the router's web management interface
- Use access control lists (ACLs) to restrict management interface access to specific trusted IP addresses
- Disable the web management interface entirely if command-line or other management methods are available
- Place vulnerable devices behind a VPN to require authentication before management interface access
# Example firewall rule to restrict access to router management interface
# Block external access to common router management ports
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
