CVE-2024-35315

Executive Summary

CVE-2024-35315 is a privilege escalation vulnerability affecting the Desktop Client of Mitel MiCollab (through version 9.7.1.110) and the MiVoice Business Solution Virtual Instance (MiVB SVI) version 1.0.0.25. An authenticated attacker can exploit improper file validation to execute arbitrary code with elevated privileges. No public proof-of-concept (PoC) or exploit code is currently available, and no official patch has been released. The vulnerability has a low EPSS score (0.0%), indicating a low probability of active exploitation in the wild at this time.

Supply Chain & Package Security

This vulnerability is not related to any open-source package ecosystem (NPM, PyPI, Go, Ruby). It affects proprietary Mitel software components.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, which is likely a placeholder. Based on the description (privilege escalation, arbitrary code execution), the actual CVSSv3 score would likely be in the High range (7.0-8.0). The vector would involve:

• Attack Vector (AV): Local (requires authenticated access)
• Attack Complexity (AC): Low
• Privileges Required (PR): Low (authenticated user)
• User Interaction (UI): None
• Scope (S): Unchanged
• Confidentiality (C): High
• Integrity (I): High
• Availability (A): High

Threat Level: High (if exploited, full system compromise is possible).

Deep Dive & Mechanics

The vulnerability resides in the file validation logic of the Desktop Client component. When an authenticated user interacts with the application (e.g., uploading, downloading, or processing files), the client fails to properly validate the file type, path, or content. This allows an attacker to craft a malicious file that, when processed by the client, triggers arbitrary code execution in the context of the application's process.

Since the application runs with elevated privileges (or can escalate to SYSTEM/root), the attacker gains those privileges. The exact mechanism is not publicly documented, but typical patterns include:

• Path Traversal: Writing a file to a privileged location (e.g., startup folder, scheduled tasks).
• DLL Hijacking: Placing a malicious DLL in a directory searched by the application before the legitimate one.
• Deserialization: Exploiting insecure deserialization of file contents.

Vulnerable vs. Patched Code

No patch is currently available. The vulnerable code is in the file handling routines of the Desktop Client. A patched version would likely include:

• Strict file extension whitelisting.
• Path canonicalization to prevent traversal.
• Content-type validation (magic bytes).
• Running file processing in a sandboxed or lower-privileged context.

Example vulnerable pseudo-code:

def process_file(file_path):
    # No validation of file extension or path
    with open(file_path, 'rb') as f:
        data = f.read()
    # Process data (e.g., deserialize)
    obj = deserialize(data)

Example patched pseudo-code:

import os
ALLOWED_EXTENSIONS = {'.txt', '.csv'}
def process_file(file_path):
    # Validate extension
    ext = os.path.splitext(file_path)[1]
    if ext not in ALLOWED_EXTENSIONS:
        raise ValueError("Invalid file type")
    # Canonicalize path to prevent traversal
    real_path = os.path.realpath(file_path)
    if not real_path.startswith('/allowed/base/dir'):
        raise ValueError("Invalid path")
    # Validate content
    with open(real_path, 'rb') as f:
        magic = f.read(4)
        if magic != b'\x89PNG':  # Example for PNG
            raise ValueError("Invalid file content")
        f.seek(0)
        data = f.read()
    # Process safely
    obj = safe_deserialize(data)

Exploitation & Lab Setup

Red Team

Prerequisites:

• Authenticated access to a vulnerable MiCollab Desktop Client (version <= 9.7.1.110) or MiVB SVI (1.0.0.25).
• Ability to upload or trigger file processing.

Exploitation Steps:

1. Reconnaissance: Identify the file upload/processing endpoint (e.g., /upload, /import).
2. Craft Payload: Create a malicious file that exploits the improper validation. For example:
   • A .lnk file pointing to a malicious executable.
   • A crafted .xml file with XXE or deserialization payload.
   • A .dll file for hijacking.
3. Upload/Trigger: Send the malicious file to the vulnerable endpoint.
4. Escalate: Once executed, the payload runs with elevated privileges, granting full control.

Example payload (DLL hijacking):

// malicious.cpp
#include <windows.h>
BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) {
    if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
        system("cmd.exe /c net user attacker Password123! /add && net localgroup Administrators attacker /add");
    }
    return TRUE;
}

Compile as malicious.dll and place it in a directory searched by the application.

Blue Team

Detection Steps:

1. Monitor File Operations: Use Sysmon or EDR to log file creation/modification events in sensitive directories (e.g., C:\Windows\System32, C:\ProgramData).
2. Analyze Process Behavior: Look for unexpected child processes spawned by the MiCollab Desktop Client (e.g., cmd.exe, powershell.exe).
3. Check for Anomalous DLL Loads: Use tools like Process Monitor to detect DLLs loaded from non-standard paths.
4. Review Authentication Logs: Identify accounts that triggered file uploads and correlate with privilege escalation events.

Hunting Query (KQL):

DeviceProcessEvents
| where InitiatingProcessFileName contains "MiCollab"
| where FileName in~ ("cmd.exe", "powershell.exe", "wscript.exe", "cscript.exe")
| project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, FileName, CommandLine

Indicators of Compromise (IOCs)

• File Hashes: (No known samples yet; placeholder)
  • malicious.dll: SHA256 e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Indicators:
  • Outbound connections to unknown IPs from the MiCollab process.
• Registry Keys:
  • HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ with suspicious entries.
• Process Anomalies:
  • MiCollabDesktopClient.exe spawning cmd.exe or powershell.exe.
• File Paths:
  • C:\Users\<user>\AppData\Local\Temp\*.dll (unexpected DLLs)
  • C:\ProgramData\Mitel\MiCollab\* (modified files)

Detection Engineering

YARA Rule

rule CVE_2024_35315_Mitel_PrivEsc {
    meta:
        description = "Detects potential exploitation of CVE-2024-35315 via malicious DLL or file"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-35315"
    strings:
        $s1 = "MiCollab" nocase
        $s2 = "MiVB SVI" nocase
        $s3 = "privilege escalation" nocase
        $s4 = "file validation" nocase
    condition:
        any of ($s*) and filesize < 10MB
}

Sigma Rule

title: CVE-2024-35315 - Mitel MiCollab Privilege Escalation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects suspicious process creation from MiCollab Desktop Client
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\MiCollabDesktopClient.exe'
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
            - '\wscript.exe'
            - '\cscript.exe'
    condition: selection
falsepositives:
    - Legitimate administrative tasks
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2024-35315 - Mitel MiCollab Potential Exploitation";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/upload"; http_uri;
    file_data;
    content:"|ff d8 ff e0|"; within:4; // JPEG magic bytes as example
    sid:1000001;
    rev:1;
    reference:cve,2024-35315;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Systems: Disconnect vulnerable MiCollab/MiVB SVI instances from the network if possible.
2. Restrict File Uploads: Disable file upload/processing features in the Desktop Client until a patch is available.
3. Apply Principle of Least Privilege: Ensure the Desktop Client runs with minimal necessary privileges (not as Administrator/SYSTEM).
4. Monitor Logs: Enable detailed logging for file operations and process creation.

Long-Term Fix:

• Await an official patch from Mitel. Contact Mitel support for updates.
• Implement application whitelisting (e.g., AppLocker) to block unauthorized executables/DLLs.
• Use a web application firewall (WAF) to filter malicious file uploads.

Workaround:

• If patching is not possible, consider replacing the Desktop Client with a web-based interface (if available) that has stricter file validation.

Valters IT
Securing Digital Frontiers