CVE-2026-4974: Tenda AC7 Buffer Overflow Vulnerability

CVE-2026-4974 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda AC7 router firmware version 15.03.06.44. The vulnerability exists in the fromSetSysTime function within the /goform/SetSysTimeCfg endpoint of the POST Request Handler component. An attacker can exploit this flaw by manipulating the Time argument, leading to a stack-based buffer overflow condition. This vulnerability is remotely exploitable and an exploit has been publicly disclosed.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow vulnerability to potentially achieve code execution on affected Tenda AC7 routers, compromising network infrastructure and enabling further lateral movement.

Affected Products

• Tenda AC7 Firmware version 15.03.06.44
• Tenda AC7 Hardware version 1.0
• Tenda AC7 Router devices running vulnerable firmware

Discovery Timeline

• 2026-03-27 - CVE-2026-4974 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2026-4974

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) and CWE-787 (Out-of-bounds Write). The fromSetSysTime function in the Tenda AC7 firmware fails to properly validate the length of user-supplied input in the Time parameter before copying it to a fixed-size stack buffer.

When a malicious POST request is sent to the /goform/SetSysTimeCfg endpoint with an oversized Time argument, the function writes beyond the allocated buffer boundaries on the stack. This memory corruption can overwrite adjacent stack data including saved return addresses, potentially allowing an attacker to hijack program execution flow.

The vulnerability is accessible over the network and requires only low-level authentication, making it particularly dangerous for exposed router management interfaces.

Root Cause

The root cause of this vulnerability is improper input validation in the fromSetSysTime function. The firmware fails to implement adequate bounds checking on the Time parameter received via POST requests. Without proper length validation, user-controlled data is copied directly to a stack buffer without verifying it fits within the allocated memory space, resulting in a classic stack-based buffer overflow condition.

Attack Vector

The attack can be conducted remotely over the network by sending a specially crafted POST request to the vulnerable endpoint. An attacker must have low-level authentication access to the router's web management interface. The exploitation process involves:

1. Identifying a Tenda AC7 router running firmware version 15.03.06.44
2. Authenticating to the router's web interface with valid credentials
3. Sending a malicious POST request to /goform/SetSysTimeCfg with an oversized Time parameter
4. The overflow corrupts stack memory, potentially allowing arbitrary code execution

The vulnerability mechanism involves improper handling of the Time parameter in the POST request body. When the fromSetSysTime function processes user input without adequate length checks, data exceeding the buffer size overwrites adjacent stack memory. Technical details and proof-of-concept information are available in the Notion Security Report.

Detection Methods for CVE-2026-4974

Indicators of Compromise

• Unusual POST requests to /goform/SetSysTimeCfg containing abnormally long Time parameter values
• Router crashes, reboots, or unexpected behavior following web interface access
• Suspicious outbound network connections from the router device
• Unauthorized configuration changes or new user accounts on the router

Detection Strategies

• Monitor HTTP traffic to router management interfaces for POST requests to /goform/SetSysTimeCfg with oversized payloads
• Implement network-based intrusion detection rules to identify buffer overflow attack patterns against Tenda devices
• Deploy web application firewall rules to filter requests with excessively long parameter values to goform endpoints
• Enable logging on router management interfaces and review for anomalous access patterns

Monitoring Recommendations

• Regularly audit network traffic to identify unauthorized access attempts to router administration interfaces
• Implement network segmentation to restrict access to router management ports from untrusted networks
• Monitor for unexpected device reboots or performance degradation that may indicate exploitation attempts
• Use network monitoring tools to detect unusual traffic patterns originating from router devices

How to Mitigate CVE-2026-4974

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management features if not required for operations
• Implement network segmentation to isolate router management interfaces from untrusted networks
• Monitor for vendor firmware updates that address this vulnerability

Patch Information

As of the last update on 2026-03-30, no official patch has been confirmed from Tenda. Organizations should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Additional vulnerability tracking information is available through VulDB #353861.

Workarounds

• Disable the web management interface entirely if not required and use console-based management instead
• Implement strict access control lists (ACLs) to limit which IP addresses can reach the router's management interface
• Place the router management interface behind a VPN to prevent direct network exposure
• Consider replacing affected devices with alternative router solutions if vendor patches are not available

# Example: Restrict management interface access via firewall rules
# Block external access to management port (adjust interface/port as needed)
iptables -A INPUT -i eth0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 443 -j DROP

# Allow management access only from trusted admin network
iptables -A INPUT -s 192.168.1.0/24 -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -p tcp --dport 443 -j ACCEPT