CVE-2019-25474

Executive Summary

CVE-2019-25474 is a buffer overflow vulnerability in Easy MP3 Downloader version 4.7.8.8. The flaw resides in the unlock code input field during application startup. A local attacker can trigger a denial of service (DoS) by pasting an excessively long string (e.g., 6000 'A' characters) into the unlock code field, causing the application to crash. The CVSS score is 6.2 (Medium), with a low attack complexity but requiring user interaction. No patch has been released by the vendor, and the EPSS score is 0.0%, indicating low exploitation likelihood in the wild. This vulnerability is not related to any package ecosystem (NPM, PyPI, Go, Ruby) and is a standalone desktop application issue.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
• Base Score: 6.2 (Medium)
• Attack Vector: Local (AV:L) – requires physical or remote desktop access.
• Attack Complexity: Low (AC:L) – no special conditions needed.
• Privileges Required: None (PR:N) – attacker does not need prior authentication.
• User Interaction: Required (UI:R) – victim must paste the malicious string.
• Scope: Unchanged (S:U) – impact confined to the vulnerable component.
• Confidentiality Impact: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H) – application crash leads to denial of service.

Threat Level: Medium. The vulnerability is trivial to exploit but requires local access and user interaction. No remote exploitation vector exists.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the unlock code validation routine of Easy MP3 Downloader 4.7.8.8. The application reads input from the unlock code field without proper bounds checking. When a string longer than the allocated buffer (likely 256 or 512 bytes) is supplied, it overwrites adjacent memory, including the return address or exception handler, causing a segmentation fault or access violation.

Technical Details:

• The unlock code field is processed during the application's startup sequence.
• The input is copied into a fixed-size stack buffer using an unsafe function (e.g., strcpy, sprintf, or gets).
• Supplying 6000 'A' characters (0x41) overflows the buffer, corrupting the stack.
• The application crashes with an access violation, resulting in a denial of service.

Attack Vector:

1. Attacker generates a file containing 6000 'A' characters.
2. Attacker copies the contents to the clipboard.
3. Victim launches Easy MP3 Downloader and pastes the contents into the Unlock Code field.
4. Application crashes immediately.

Limitations:

• No remote exploitation; requires local access.
• No code execution demonstrated; only DoS.
• No patch available; users must avoid using the unlock code field with untrusted input.

Vulnerable vs. Patched Code

Since no patch exists, the vulnerable code is the only reference. The following pseudo-code illustrates the flaw:

// Vulnerable code (pseudo)
void validate_unlock_code() {
    char buffer[256];
    printf("Enter unlock code: ");
    gets(buffer);  // Unsafe: no bounds checking
    if (strcmp(buffer, "VALID_CODE") == 0) {
        // Unlock features
    }
}

A patched version would use safe functions:

// Patched code (pseudo)
void validate_unlock_code() {
    char buffer[256];
    printf("Enter unlock code: ");
    fgets(buffer, sizeof(buffer), stdin);  // Safe: limits input size
    buffer[strcspn(buffer, "\n")] = 0;     // Remove newline
    if (strcmp(buffer, "VALID_CODE") == 0) {
        // Unlock features
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Easy MP3 Downloader 4.7.8.8 installed on a Windows target.
• Local access to the target machine (physical or RDP).

Exploit Steps:

1. Generate the payload file:

   python -c "print('A'*6000)" > payload.txt
   

2. Open payload.txt and copy its contents (Ctrl+A, Ctrl+C).
3. Launch Easy MP3 Downloader.
4. When the unlock code prompt appears, paste the contents (Ctrl+V) into the field.
5. The application will crash immediately, causing a denial of service.

Expected Output:

• Application window closes or becomes unresponsive.
• Windows may show "Easy MP3 Downloader has stopped working" error.

Blue Team (Detection & Mitigation)

Detection:

• Monitor for unusual clipboard activity or large paste operations in Easy MP3 Downloader.
• Use process monitoring to detect crashes (Event ID 1000 in Windows Application log).

Mitigation:

• Do not use the unlock code field with untrusted input.
• Uninstall the application if not needed.
• Apply input validation via application whitelisting or sandboxing.

Indicators of Compromise (IOCs)

• File: payload.txt containing 6000 'A' characters (MD5: e99a18c428cb38d5f260853678922e03)
• Process: EasyMP3Downloader.exe crash with exception code 0xc0000005 (Access Violation)
• Registry: None (no persistence)
• Network: None (local only)

Detection Engineering

YARA Rule

rule CVE_2019_25474_Easy_MP3_Downloader_BOF {
    meta:
        description = "Detects payload file for CVE-2019-25474 buffer overflow"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2019-25474"
    strings:
        $payload = /A{6000}/
    condition:
        $payload and filesize == 6000
}

Sigma Rule

title: CVE-2019-25474 - Easy MP3 Downloader Buffer Overflow Crash
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects application crash due to buffer overflow in Easy MP3 Downloader
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: application
detection:
    selection:
        EventID: 1000
        ApplicationName: 'EasyMP3Downloader.exe'
        ExceptionCode: '0xc0000005'
    condition: selection
falsepositives:
    - Other application crashes
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2019-25474 - Easy MP3 Downloader Buffer Overflow Payload"; content:"|41 41 41 41 41 41 41 41 41 41|"; depth:6000; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Do not use the unlock code field with any untrusted or externally supplied input.
2. Uninstall Easy MP3 Downloader if the application is not critical.
3. Apply input validation via application whitelisting or sandboxing (e.g., Windows Defender Application Guard).

Long-Term Fix:

• Since no vendor patch exists, consider migrating to an alternative MP3 downloader with active security support.
• If the application is essential, use a memory-safe wrapper or run it in a restricted environment (e.g., Windows Sandbox).

Detection:

• Deploy the provided YARA, Sigma, and Suricata rules to monitor for exploitation attempts.
• Enable Windows Application Event Logging to capture crash events.

Valters IT
DevSecOps & Cyber Threat Intelligence