CVE-2025-4532: SunloginClient Path Traversal Vulnerability

CVE-2025-4532 Overview

CVE-2025-4532 is an uncontrolled search path vulnerability [CWE-426] in Shanghai Bairui Information Technology SunloginClient version 15.8.3.19819. The flaw resides in the process.dll library loaded by sunlogin_guard.exe. An attacker with local access can place a malicious DLL in a location searched before the legitimate library, causing the guard process to load attacker-controlled code. The exploit has been publicly disclosed. The vendor was contacted early about this disclosure but did not respond.

Critical Impact

Successful exploitation allows a local attacker to execute arbitrary code in the context of the Sunlogin guard process, compromising confidentiality, integrity, and availability on the affected host.

Affected Products

• Shanghai Bairui Information Technology SunloginClient 15.8.3.19819
• Component: process.dll loaded by sunlogin_guard.exe
• Platform: Windows (Sunlogin remote access client)

Discovery Timeline

• 2025-05-11 - CVE-2025-4532 published to NVD
• 2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-4532

Vulnerability Analysis

The vulnerability is an uncontrolled search path issue [CWE-426] in the Sunlogin remote access client. The sunlogin_guard.exe process resolves and loads the process.dll library without fully qualifying the search path or validating the loaded module. When Windows resolves a DLL name without an absolute path, it walks a defined search order that can include the application directory and other writable locations. An attacker who can drop a file in one of those directories can supply a malicious DLL that the guard process will load in place of the legitimate one.

Exploitation requires local access and elevated attack complexity, which limits opportunistic abuse but keeps the flaw useful for post-compromise persistence and privilege manipulation. The vendor has not published an advisory or patch response.

Root Cause

The root cause is improper control of the search path used to locate process.dll. The guard binary does not enforce a fully qualified path, does not apply SetDefaultDllDirectories restrictions, and does not validate the signature of the loaded module before mapping it into the process.

Attack Vector

A local attacker plants a crafted process.dll in a directory that precedes the legitimate library in the Windows DLL search order. When sunlogin_guard.exe starts or reloads the dependency, the loader binds to the attacker's DLL. The malicious DllMain then executes with the privileges of the guard process. Because exploitation depends on filesystem write access to a searched directory and specific startup conditions, the reported exploitability is difficult.

No verified proof-of-concept code is available. Technical details are described in the VulDB entry and the Yuque security analysis.

Detection Methods for CVE-2025-4532

Indicators of Compromise

• Presence of an unsigned or unexpected process.dll in the Sunlogin installation directory or any directory in the DLL search path of sunlogin_guard.exe.
• sunlogin_guard.exe loading a process.dll whose path or digital signature does not match the vendor-shipped binary.
• Child processes or network connections originating from sunlogin_guard.exe that deviate from historical baselines.

Detection Strategies

• Monitor image load events (Sysmon Event ID 7) for sunlogin_guard.exe loading process.dll from unexpected paths or without a valid Shanghai Bairui signature.
• Alert on file writes to the Sunlogin installation directory by processes other than the installer or update service.
• Hunt for DLL planting patterns using CreateFile and LoadLibrary telemetry against known-good baselines.

Monitoring Recommendations

• Baseline hashes of process.dll shipped with SunloginClient and alert on deviation.
• Track parent-child process relationships for sunlogin_guard.exe to identify unexpected code execution.
• Ingest Windows loader and Sysmon events into a centralized SIEM for correlation across endpoints running Sunlogin.

How to Mitigate CVE-2025-4532

Immediate Actions Required

• Inventory endpoints running SunloginClient 15.8.3.19819 and evaluate whether the client is required for business operations.
• Restrict filesystem permissions on the Sunlogin installation directory so only administrators can write files.
• Consider uninstalling or blocking Sunlogin on systems where remote support functionality is not required.

Patch Information

The vendor did not respond to disclosure and has not published a patch or advisory for CVE-2025-4532 at the time of writing. Monitor the VulDB entry and Shanghai Bairui update channels for future fixes.

Workarounds

• Run SunloginClient under a low-privilege account so DLL hijacking does not yield elevated code execution.
• Apply application allowlisting (WDAC or AppLocker) to block loading of unsigned DLLs by sunlogin_guard.exe.
• Remove write permissions for standard users on any directory in the DLL search path of sunlogin_guard.exe.

# Restrict write access to the Sunlogin installation directory (Windows, run as admin)
icacls "C:\Program Files\Oray\SunLogin\SunloginClient" /inheritance:r
icacls "C:\Program Files\Oray\SunLogin\SunloginClient" /grant:r Administrators:(OI)(CI)F SYSTEM:(OI)(CI)F "Users":(OI)(CI)RX