CVE-2025-5850: Tenda AC15 Buffer Overflow Vulnerability

CVE-2025-5850 Overview

CVE-2025-5850 is a buffer overflow vulnerability in the Tenda AC15 router running firmware version 15.03.05.19_multi. The flaw resides in the formsetschedled function within the /goform/SetLEDCf endpoint handled by the HTTP POST Request Handler. Attackers can manipulate the Time argument to trigger memory corruption. The vulnerability is exploitable remotely over the network and requires only low privileges. Public disclosure of the exploit technique increases the urgency for patching or mitigating affected devices.

Critical Impact
Remote attackers with low privileges can trigger a buffer overflow in the Tenda AC15 HTTP service, leading to potential remote code execution or denial of service on the device.

Affected Products

Tenda AC15 router (hardware version 1.0)
Tenda AC15 firmware 15.03.05.19_multi
HTTP POST Request Handler component (/goform/SetLEDCf)

Discovery Timeline

2025-06-08 - CVE-2025-5850 published to NVD
2025-06-09 - Last updated in NVD database

Technical Details for CVE-2025-5850

Vulnerability Analysis

The vulnerability exists in the formsetschedled function, which processes scheduled LED configuration requests sent to the /goform/SetLEDCf endpoint. The function fails to validate the length of the Time parameter supplied through HTTP POST requests. When an attacker submits an oversized Time value, the data overflows a fixed-size buffer on the stack or heap. This corruption can overwrite adjacent memory, control flow structures, or function return addresses on the device.

Tenda AC15 routers run a Linux-based firmware on a MIPS architecture without modern exploit mitigations such as full ASLR or stack canaries on every binary. The lack of bounds checking is classified as [CWE-119], improper restriction of operations within the bounds of a memory buffer. Successful exploitation can yield arbitrary code execution in the context of the web management daemon, which typically runs as root.

Root Cause

The formsetschedled handler copies the attacker-controlled Time argument into a stack buffer without enforcing a maximum length. No strncpy boundary, no input sanitizer, and no length precheck guards the destination buffer. This pattern is recurrent across multiple /goform/ handlers in Tenda AC-series firmware.

Attack Vector

An attacker reachable on the network sends a crafted HTTP POST request to /goform/SetLEDCf containing an oversized Time parameter. The request requires authenticated access to the web management interface, but default and weak credentials remain common on consumer routers. Once the overflow triggers, the attacker can crash the httpd process or pivot toward code execution. See the Notion Security Documentation and VulDB entry #311596 for technical details.

// No verified proof-of-concept code is published.
// The vulnerability is triggered by sending an HTTP POST request to
// /goform/SetLEDCf with an over-length value in the Time parameter.

Detection Methods for CVE-2025-5850

Indicators of Compromise

HTTP POST requests targeting /goform/SetLEDCf with unusually large Time parameter values
Repeated crashes or restarts of the httpd process on Tenda AC15 devices
Outbound connections from the router to unfamiliar hosts following a configuration request
Web management interface logs showing malformed scheduled LED configuration submissions

Detection Strategies

Inspect network traffic for HTTP POST bodies sent to /goform/SetLEDCf containing Time field values exceeding expected length (typical scheduling strings are under 64 bytes)
Deploy IDS or IPS signatures that flag oversized parameters in Tenda /goform/ endpoint traffic
Correlate authentication events with subsequent administrative endpoint requests to identify credential abuse

Monitoring Recommendations

Capture and review router system logs for daemon crash entries and unexpected reboots
Monitor for anomalous DNS queries or outbound connections originating from router management IP addresses
Track inbound HTTP traffic to router management interfaces from non-trusted network segments

How to Mitigate CVE-2025-5850

Immediate Actions Required

Restrict access to the router's web management interface to trusted local network segments only
Disable remote (WAN-side) administration on the Tenda AC15 device
Replace default and weak administrator credentials with strong, unique passwords
Audit network exposure of all Tenda AC15 devices and isolate them from sensitive internal assets

Patch Information

No vendor patch has been published in the referenced advisories at the time of CVE assignment. Monitor the Tenda Official Website for firmware updates addressing the formsetschedled handler. Consider replacing end-of-life or unsupported Tenda AC15 hardware where vendor remediation is unavailable.

Workarounds

Place affected routers behind a network firewall that blocks untrusted HTTP traffic to the management port
Segment IoT and consumer networking equipment onto a dedicated VLAN to limit blast radius
Use network access control lists to permit administrative HTTP requests only from specific management workstations
Where feasible, replace the device with a model that receives current security updates

bash

# Example: block external access to the router management interface
# (run on an upstream firewall, not the router itself)
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -i <wan_iface> -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -i <wan_iface> -j DROP