CVE-2026-4902: Tenda AC5 Buffer Overflow Vulnerability

CVE-2026-4902 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC5 firmware version 15.03.06.47. This vulnerability affects the fromAddressNat function within the /goform/addressNat endpoint of the POST Request Handler component. The manipulation of the page argument enables remote attackers to trigger a stack-based buffer overflow, potentially leading to arbitrary code execution or denial of service on affected devices.

Critical Impact

Remote attackers can exploit this vulnerability over the network to compromise Tenda AC5 routers by sending crafted POST requests to the vulnerable endpoint, potentially gaining full control of the device.

Affected Products

• Tenda AC5 Firmware version 15.03.06.47
• Tenda AC5 devices running vulnerable POST Request Handler component

Discovery Timeline

• 2026-03-26 - CVE-2026-4902 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-4902

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The fromAddressNat function in the Tenda AC5 router firmware fails to properly validate the length of user-supplied input provided through the page parameter. When a malicious actor sends an overly long string via the page argument in a POST request to /goform/addressNat, the function writes beyond the allocated stack buffer boundaries.

The vulnerability is exploitable remotely over the network without requiring user interaction. An attacker with low-level privileges can craft and send malicious POST requests to the affected endpoint. The public availability of exploit information increases the risk of active exploitation against unpatched devices.

Root Cause

The root cause stems from improper bounds checking in the fromAddressNat function when processing the page parameter from incoming POST requests. The firmware code does not validate the length of the input data before copying it to a fixed-size stack buffer, resulting in a classic stack-based buffer overflow condition. This lack of input validation allows attackers to overwrite adjacent memory locations on the stack, including return addresses and saved registers.

Attack Vector

The attack vector is network-based, allowing remote exploitation without physical access to the device. An attacker can send specially crafted HTTP POST requests to the /goform/addressNat endpoint with an oversized page parameter value. The crafted payload overwrites the stack buffer and can manipulate the program's control flow. This could enable arbitrary code execution with the privileges of the web server process, or cause a denial of service by crashing the affected service.

The exploitation process involves sending a POST request to the vulnerable endpoint with a carefully constructed payload in the page parameter. The payload would include padding to fill the buffer, followed by data to overwrite the return address and redirect execution to attacker-controlled code. Technical details regarding the vulnerability can be found in the Notion Page on Tenda AC5.

Detection Methods for CVE-2026-4902

Indicators of Compromise

• Unusual POST requests to /goform/addressNat with abnormally large page parameter values
• Web server crashes or unexpected reboots on Tenda AC5 devices
• Suspicious outbound network connections originating from the router following exploitation attempts
• Unexpected modifications to router configuration or firmware

Detection Strategies

• Monitor HTTP traffic for POST requests to /goform/addressNat containing excessively long parameter values
• Implement intrusion detection signatures to identify buffer overflow attempts targeting the page parameter
• Deploy network monitoring to detect anomalous traffic patterns to/from Tenda AC5 router management interfaces
• Audit logs for repeated failed requests or unusual access patterns to router administration endpoints

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic destined for router management ports
• Configure alerting for abnormal request sizes or patterns targeting embedded device web interfaces
• Establish baseline behavior for router management traffic and alert on deviations
• Monitor for firmware integrity changes or unauthorized configuration modifications

How to Mitigate CVE-2026-4902

Immediate Actions Required

• Restrict network access to the Tenda AC5 web management interface to trusted IP addresses only
• Disable remote management access if not required for operations
• Implement network segmentation to isolate affected devices from untrusted networks
• Monitor affected devices for signs of compromise until patching is possible

Patch Information

As of the publication date, no official patch information has been released by Tenda. Organizations should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Additional vulnerability tracking information is available at VulDB ID #353653.

Workarounds

• Disable the web management interface and use alternative management methods if available
• Place affected routers behind a firewall that filters incoming requests to /goform/addressNat
• Implement access control lists (ACLs) to restrict management interface access to authorized administrators only
• Consider replacing vulnerable devices with patched alternatives if no firmware update becomes available

# Example firewall rule to block external access to vulnerable endpoint
# (Adjust based on your firewall solution)
iptables -A INPUT -p tcp --dport 80 -m string --string "/goform/addressNat" --algo bm -j DROP
iptables -A INPUT -p tcp --dport 443 -m string --string "/goform/addressNat" --algo bm -j DROP