CVE-2019-25551

Executive Summary

CVE-2019-25551 is a denial of service (DoS) vulnerability affecting Sandboxie version 5.30. The flaw resides in the program alert configuration feature, where a local attacker can cause the application to crash by pasting an excessively long string (5000 characters) into the "Select or enter a program" field. This vulnerability requires local access and does not lead to privilege escalation or data compromise, but it can disrupt the sandboxing service, potentially impacting system stability for users relying on Sandboxie for isolation.

This vulnerability is classified as a low-severity issue due to the requirement for local access and the limited impact (application crash). No public exploit code or automated scanning templates are available, and the vendor has not released a patch. The attack vector is straightforward, making it a trivial denial-of-service vector for local attackers.

CVSS Breakdown & Threat Level

• CVSS Score: 5.5 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
• Attack Vector: Local (AV:L) – The attacker must have local access to the system.
• Attack Complexity: Low (AC:L) – No special conditions are required; the attack is simple to execute.
• Privileges Required: Low (PR:L) – The attacker needs a standard user account.
• User Interaction: None (UI:N) – No victim interaction is needed.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H) – The application crashes, causing a denial of service.

Threat Level: Low. The vulnerability is limited to local denial of service and does not enable remote exploitation or data theft. It is primarily a nuisance for multi-user environments or systems where Sandboxie is critical.

Deep Dive & Mechanics

The vulnerability is a classic input validation flaw in Sandboxie's configuration interface. The "Program Alerts" feature allows users to specify which programs should trigger alerts when they attempt to access the sandbox. The input field for program names lacks proper length validation.

When a user pastes a string of 5000 characters into this field, the application attempts to process the excessively long input. This likely causes a buffer overflow or memory exhaustion within the application's string handling routines, leading to a crash. The crash is immediate and does not require any special conditions beyond the long input.

The root cause is the absence of input length checks. The application should truncate or reject strings exceeding a reasonable length (e.g., 256 characters). The vulnerability is trivial to reproduce and does not require any exploit development skills.

Vulnerable vs. Patched Code

No patched version has been released by the vendor. The vulnerable code is in the configuration dialog for program alerts. A hypothetical fix would involve adding input validation to limit the length of the program name field.

Vulnerable Code (Conceptual):

// No length check
char program_name[256];
GetDlgItemText(hDlg, IDC_PROGRAM_NAME, program_name, sizeof(program_name));
// Process program_name...

Patched Code (Conceptual):

char program_name[256];
if (GetDlgItemText(hDlg, IDC_PROGRAM_NAME, program_name, sizeof(program_name)) >= sizeof(program_name)) {
    // Truncate or reject
    MessageBox(hDlg, "Program name too long", "Error", MB_OK);
    return;
}
// Process program_name...

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a Windows system running Sandboxie 5.30.
• A standard user account.

Steps:

1. Launch Sandboxie.
2. Navigate to Configure > Program Alerts.
3. In the "Select or enter a program" field, paste a string of 5000 characters (e.g., A repeated 5000 times).
4. Click Add or press Enter.
5. Sandboxie will crash immediately.

Proof of Concept (Python):

# Generate 5000 'A' characters
payload = "A" * 5000
print(payload)
# Copy the output and paste into the program name field in Sandboxie

Blue Team

Detection:

• Monitor for Sandboxie crashes in Windows Event Log (Application logs, Event ID 1000 for application errors).
• Look for repeated attempts to add long strings to the program alerts configuration.
• Use process monitoring to detect abnormal memory usage or crashes of SbieCtrl.exe or Sandboxie.exe.

Prevention:

• Restrict local user permissions to prevent modification of Sandboxie configuration.
• Use application whitelisting to block untrusted users from running Sandboxie.
• Apply input validation at the network level if Sandboxie is managed remotely (unlikely).

Indicators of Compromise (IOCs)

• Application Crash: Sandboxie (SbieCtrl.exe or Sandboxie.exe) crashes with exception code 0xc0000005 (access violation) or similar.
• Event Log Entry: Windows Event ID 1000 with faulting module SbieCtrl.exe or Sandboxie.exe.
• Configuration File: The Sandboxie.ini file may contain an excessively long entry under [ProgramAlerts] or similar section.

Detection Engineering

YARA Rule

rule CVE_2019_25551_Sandboxie_DoS {
    meta:
        description = "Detects Sandboxie configuration files with excessively long program alert entries"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2019-25551"
    strings:
        $long_string = /[A-Za-z0-9]{5000,}/ 
    condition:
        $long_string and (filename contains "Sandboxie.ini" or filename contains "Sandboxie")
}

Sigma Rule

title: Sandboxie Crash Due to Long Program Alert Input
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects Sandboxie crashes caused by excessively long input in program alert configuration
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: application
detection:
    selection:
        EventID: 1000
        Provider_Name: 'Application Error'
        Faulting_Module: 'SbieCtrl.exe' or 'Sandboxie.exe'
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: low

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2019-25551 Sandboxie DoS Attempt"; flow:to_server; content:"|41 41 41 41 41 41 41 41 41 41|"; distance:0; within:5000; classtype:attempted-dos; sid:1000001; rev:1;)

Note: This Suricata rule is theoretical as the attack is local. It would only apply if the configuration is sent over the network (e.g., via a management interface).

Remediation & Mitigation

Immediate Actions:

1. Upgrade: Check for any newer versions of Sandboxie that may have addressed this issue. If none, consider migrating to an alternative sandboxing solution.
2. Restrict Access: Limit local user accounts that can modify Sandboxie configuration. Use Group Policy to enforce this.
3. Input Validation: If you have access to the source code, implement input length validation for the program name field.

Long-Term Fix:

• The vendor should release a patch that limits the input length to a safe value (e.g., 256 characters) and handles overflow gracefully.

Workaround:

• Disable the "Program Alerts" feature if not needed, or use a script to monitor and truncate long entries in the configuration file.

Valters IT