CVE-2025-5863: Tenda AC5 Buffer Overflow Vulnerability

CVE-2025-5863 Overview

A critical stack-based buffer overflow vulnerability has been identified in the Tenda AC5 router firmware version 15.03.06.47. The vulnerability exists within the formSetRebootTimer function located in the /goform/SetRebootTimer endpoint. Improper handling of the rebootTime argument allows an authenticated remote attacker to overflow the stack buffer, potentially leading to arbitrary code execution or denial of service on vulnerable devices.

Critical Impact

Remote attackers with low-level privileges can exploit this stack-based buffer overflow to execute arbitrary code, compromise router integrity, and potentially gain complete control over the network device.

Affected Products

• Tenda AC5 Firmware version 15.03.06.47
• Tenda AC5 Hardware version 1.0
• Tenda AC5 Router

Discovery Timeline

• June 9, 2025 - CVE-2025-5863 published to NVD
• June 9, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5863

Vulnerability Analysis

This vulnerability is a classic stack-based buffer overflow (CWE-787: Out-of-bounds Write, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) affecting the Tenda AC5 router's web management interface. The vulnerable function formSetRebootTimer fails to properly validate the length of user-supplied input for the rebootTime parameter before copying it into a fixed-size stack buffer.

When an attacker submits an oversized value for the rebootTime argument via an HTTP request to /goform/SetRebootTimer, the input exceeds the allocated buffer space on the stack. This overflow can overwrite critical stack data including saved return addresses and frame pointers, enabling control flow hijacking. The network-accessible nature of this endpoint combined with the low attack complexity makes this vulnerability particularly dangerous for exposed devices.

Root Cause

The root cause of this vulnerability lies in the absence of proper input length validation within the formSetRebootTimer function. The firmware accepts user-controlled data from the rebootTime HTTP parameter and copies it directly into a stack-allocated buffer without verifying that the input length does not exceed the buffer's capacity. This classic unsafe memory operation pattern allows attackers to write beyond the intended memory boundaries.

Attack Vector

The attack can be executed remotely over the network by sending a specially crafted HTTP POST request to the /goform/SetRebootTimer endpoint on the router's web management interface. The attacker must have low-level privileges (authentication) but requires no user interaction. The exploit involves manipulating the rebootTime parameter with an excessively long payload designed to overflow the stack buffer and overwrite control data.

The vulnerability has been publicly disclosed, and technical details are available through external security documentation. Attackers can craft HTTP requests containing malicious payloads in the rebootTime field to trigger the overflow condition. For detailed technical analysis and proof-of-concept information, refer to the Security Documentation.

Detection Methods for CVE-2025-5863

Indicators of Compromise

• Unusual HTTP POST requests to /goform/SetRebootTimer with abnormally long rebootTime parameter values
• Router crashes, reboots, or unexpected behavior following web interface access
• Network traffic anomalies indicating exploitation attempts against the router management interface
• Suspicious outbound connections from the router indicating potential compromise

Detection Strategies

• Implement intrusion detection system (IDS) rules to monitor for HTTP requests to /goform/SetRebootTimer containing payloads exceeding normal parameter lengths
• Configure web application firewall (WAF) rules to block requests with oversized input values to vulnerable endpoints
• Enable logging on the router management interface to capture and analyze suspicious access patterns
• Deploy network monitoring to detect anomalous behavior from Tenda AC5 devices

Monitoring Recommendations

• Monitor network traffic for HTTP POST requests targeting /goform/SetRebootTimer with unusually large payloads
• Set up alerts for router instability, unexpected reboots, or management interface unavailability
• Review router access logs regularly for unauthorized or unusual administrative access attempts
• Monitor for firmware integrity changes or unauthorized configuration modifications

How to Mitigate CVE-2025-5863

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Disable remote management features if not required for operations
• Implement network segmentation to isolate vulnerable devices from untrusted networks
• Place the router behind a firewall that filters malicious requests to the management interface
• Monitor for vendor firmware updates and apply patches as soon as available

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Administrators should monitor the Tenda Official Website for security updates and firmware releases. Additional vulnerability tracking information is available through VulDB #311622.

Workarounds

• Disable the web management interface if not actively required for administration
• Restrict management interface access to specific trusted IP addresses using firewall rules
• Consider replacing vulnerable devices with alternative hardware that receives regular security updates
• Implement a network access control solution to limit which devices can communicate with the router's management interface

# Example: Restrict management interface access via firewall rules
# Block external access to router management port (adjust IP and port as needed)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Alternative: Use network segmentation to isolate management interface
# Configure VLAN to separate management traffic from general network access