CVE-2025-63945

Executive Summary

CVE-2025-63945 is a privilege escalation vulnerability in the Tencent iOA application on Windows, affecting versions up to and including 210.9.28693.621001. The vulnerability allows a local user to execute programs with elevated privileges by exploiting a race condition. The attack requires local access and a successful race condition exploitation, making it a medium-complexity local privilege escalation (LPE) threat. No public proof-of-concept (PoC) or exploit code has been identified at this time, and the patch status remains unknown.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a native Windows application vulnerability.

CVSS Breakdown & Threat Level

CVSS Score: 7.0 (High) Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

• Attack Vector (AV): Local (L) – The attacker must have local access to the system.
• Attack Complexity (AC): High (H) – Successful exploitation requires a race condition, which is difficult to achieve reliably.
• Privileges Required (PR): Low (L) – The attacker needs a standard user account.
• User Interaction (UI): None (N) – No user interaction is required beyond the attacker's own actions.
• Scope (S): Unchanged (U) – The vulnerable component and the impacted component are the same.
• Confidentiality (C): High (H) – Full read access to system files and data.
• Integrity (I): High (H) – Full write access to system files and data.
• Availability (A): High (H) – Full ability to disrupt system operations.

Threat Level: High. While the attack complexity is high, successful exploitation grants SYSTEM-level privileges, allowing complete compromise of the affected Windows host.

Deep Dive & Mechanics

The vulnerability resides in the Tencent iOA application's privilege escalation mechanism. The application likely runs with high privileges (e.g., SYSTEM) to perform its functions. A race condition exists in the way iOA handles file operations or process creation when a local user triggers a specific action.

Technical Breakdown:

1. Race Condition: The vulnerability is a classic Time-of-Check Time-of-Use (TOCTOU) race condition. The application checks a condition (e.g., file existence, permissions) and then acts on that condition. Between the check and the use, a local attacker can modify the state (e.g., replace a file with a symbolic link to a privileged location).
2. Privilege Escalation: By winning the race, the attacker can cause the high-privilege iOA process to perform an operation on a file or resource that the attacker controls. This could involve:
   • Creating a symbolic link from a temporary file to a system-critical file (e.g., C:\Windows\System32\config\SAM).
   • Writing attacker-controlled data to a location that will be executed by the system (e.g., a DLL placed in a directory searched by a SYSTEM-level service).
   • Executing an arbitrary binary with SYSTEM privileges.
3. Attack Vector: The attacker must be logged into the Windows system as a standard user. They then trigger the vulnerable functionality in iOA while simultaneously performing the race condition attack (e.g., using a script that repeatedly creates and deletes files or symbolic links).

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is likely in the iOA service or driver that handles privileged operations. A typical vulnerable pattern might look like:

Vulnerable Code (Conceptual):

// Vulnerable TOCTOU pattern
if (CheckFilePermissions(userFilePath)) {
    // Race window: attacker replaces userFilePath with a symlink
    HANDLE hFile = CreateFile(userFilePath, ...); // Opens the attacker's symlink
    WriteToPrivilegedLocation(hFile, data);
}

Patched Code (Conceptual):

// Patched: Use secure file operations with impersonation
HANDLE hFile = CreateFile(userFilePath, ...); // Open first
if (hFile != INVALID_HANDLE_VALUE) {
    // Verify the opened file is the intended one (e.g., using file ID)
    if (VerifyFileIdentity(hFile, expectedFileId)) {
        WriteToPrivilegedLocation(hFile, data);
    }
    CloseHandle(hFile);
}

The patched version would eliminate the race window by opening the file first and then verifying its identity, or by using operating system primitives like NtCreateFile with appropriate flags to prevent symbolic link traversal.

Exploitation & Lab Setup

Red Team

Objective: Escalate privileges from a standard user to SYSTEM on a Windows host running Tencent iOA <= 210.9.28693.621001.

Prerequisites:

• Local access to the target Windows machine.
• A standard user account.
• Tencent iOA installed and running.

Exploitation Steps (Conceptual):

1. Identify the Race Window: Use Process Monitor (Procmon) to observe file operations performed by the iOA process when a specific action is triggered (e.g., connecting to VPN, updating policies).
2. Develop the Exploit: Create a script (e.g., PowerShell or C++) that:
   • Continuously monitors for the creation of a temporary file by iOA.
   • When detected, rapidly replaces that file with a symbolic link pointing to a target file (e.g., C:\Windows\System32\drivers\etc\hosts or a system DLL).
   • Simultaneously triggers the iOA action to write to the temporary file.
3. Win the Race: Run the exploit in a loop until the race is won. Successful exploitation will result in iOA writing attacker-controlled data to the privileged location.
4. Execute Payload: If the target is a DLL, use a technique like DLL hijacking to execute code. If the target is a configuration file, modify it to execute a command as SYSTEM.

Example Exploit Skeleton (PowerShell):

# This is a conceptual example. Actual exploitation requires precise timing.
$targetPath = "C:\ProgramData\Tencent\iOA\temp\update.tmp"
$symlinkTarget = "C:\Windows\System32\drivers\etc\hosts"

while ($true) {
    if (Test-Path $targetPath) {
        Remove-Item $targetPath -Force
        New-Item -ItemType SymbolicLink -Path $targetPath -Target $symlinkTarget -Force
        # Trigger iOA action here (e.g., via COM or CLI)
        Start-Process "C:\Program Files\Tencent\iOA\iOA.exe" -ArgumentList "--trigger-update"
        Start-Sleep -Milliseconds 100
    }
}

Blue Team

Detection & Response:

1. Monitor for Symbolic Link Creation: Use Sysmon Event ID 7 (Image loaded) and Event ID 11 (FileCreate) to detect creation of symbolic links in sensitive directories.
2. Audit Process Creation: Enable Windows Event Logging for process creation (Event ID 4688) and command-line auditing. Look for iOA processes spawning unexpected child processes (e.g., cmd.exe, powershell.exe).
3. File Integrity Monitoring: Deploy FIM on critical system files (e.g., hosts, SAM, SYSTEM) to detect unauthorized modifications.
4. Race Condition Detection: High-frequency file operations on the same path by different processes (iOA and an unknown process) within a short time window can indicate a race condition attack.

Indicators of Compromise (IOCs)

• File System:
  • Unexpected symbolic links in C:\ProgramData\Tencent\iOA\ or C:\Users\<username>\AppData\Local\Tencent\iOA\.
  • Modification of system files like C:\Windows\System32\drivers\etc\hosts, C:\Windows\System32\config\SAM, or C:\Windows\System32\config\SYSTEM.
• Process:
  • iOA.exe or its child processes (e.g., iOAUpdate.exe) spawning cmd.exe, powershell.exe, or rundll32.exe with unusual arguments.
  • High-frequency file system operations by iOA.exe on temporary paths.
• Network:
  • Unusual outbound connections from the iOA process to non-standard IP addresses or domains (potential C2).

Detection Engineering

YARA Rule

rule CVE_2025_63945_Tencent_iOA_RaceCondition {
    meta:
        description = "Detects potential exploitation of CVE-2025-63945 via symbolic link creation in Tencent iOA directories"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-63945"
        hash = "unknown"
    strings:
        $s1 = "\\Tencent\\iOA\\" nocase
        $s2 = "SymbolicLink" nocase
        $s3 = "\\??\\" nocase  // NT symbolic link prefix
    condition:
        $s1 and ($s2 or $s3)
}

Sigma Rule

title: Potential CVE-2025-63945 Exploitation - Symbolic Link Creation in Tencent iOA
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects creation of symbolic links in Tencent iOA directories, which may indicate exploitation of a race condition for privilege escalation.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-63945
logsource:
    product: windows
    service: sysmon
    definition: 'Requires Sysmon Event ID 11 (FileCreate) with command-line logging enabled'
detection:
    selection:
        EventID: 11
        TargetFilename|contains: '\\Tencent\\iOA\\'
        TargetFilename|endswith: '.lnk'  # Symbolic links often have .lnk extension
    condition: selection
falsepositives:
    - Legitimate iOA updates or installations
level: high
tags:
    - attack.privilege_escalation
    - attack.t1068

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2025-63945 Potential Tencent iOA Exploitation - Unusual Outbound Connection";
    flow:to_server,established;
    content:"Tencent"; http_user_agent;
    pcre:"/iOA/i";
    sid:10000001;
    rev:1;
    metadata:created_at 2025-04-10, updated_at 2025-04-10;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Systems: If exploitation is suspected, disconnect the host from the network to prevent lateral movement.
2. Apply Principle of Least Privilege: Ensure users run with standard user accounts, not local administrators.
3. Monitor iOA Processes: Use EDR to monitor iOA.exe and its child processes for anomalous behavior.

Long-Term Remediation:

1. Vendor Patch: Contact Tencent for a patched version. No patch is currently available.
2. Application Control: Use AppLocker or Windows Defender Application Control (WDAC) to block execution of untrusted binaries.
3. Disable Unnecessary Features: If iOA is not critical, consider removing or disabling it until a patch is available.
4. File System Hardening: Enable Windows Defender Exploit Guard (ASR rules) to block symbolic link creation from untrusted processes.

Workaround: If iOA must be used, restrict the application's execution context using a low-privilege service account or run it in a sandboxed environment (e.g., Windows Sandbox).

Valters IT
Securing Digital Frontiers