CVE-2025-9871

Executive Summary

CVE-2025-9871 is a high-severity (CVSS 7.8) local privilege escalation vulnerability in Razer Synapse 3, specifically within the Razer Chroma SDK installer. The flaw allows an attacker with low-privileged code execution on a target system to escalate privileges to SYSTEM by abusing a symbolic link (symlink) following weakness. By creating a crafted symlink, the attacker can force the installer to delete arbitrary files, which can then be leveraged for code execution at the highest privilege level. This vulnerability was reported through the Zero Day Initiative (ZDI-CAN-26373) and currently has no known patch or public exploit code.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary Windows desktop application (Razer Synapse 3) and its associated Chroma SDK installer. The supply chain risk is limited to the distribution channel of Razer software; users should only download Synapse from official Razer sources.

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: 7.8 (High)
• Attack Vector: Local (AV:L) – Requires physical or remote access to the system.
• Attack Complexity: Low (AC:L) – No special conditions needed beyond standard user access.
• Privileges Required: Low (PR:L) – Attacker must have initial low-privileged code execution.
• User Interaction: None (UI:N) – No user action required beyond the attacker’s own actions.
• Scope: Unchanged (S:U) – The vulnerable component and the impacted component are the same.
• Confidentiality, Integrity, Availability Impact: All High (C:H/I:H/A:H) – Full system compromise is possible.

Threat Level: High. While the EPSS score is 0.0% (indicating low exploitation likelihood currently), the impact is severe. Local privilege escalation vulnerabilities in widely deployed gaming software are attractive targets for malware and post-exploitation toolkits.

Deep Dive & Mechanics

The vulnerability resides in the Razer Chroma SDK installer component of Razer Synapse 3. The installer performs file operations (likely deletion of temporary or old files) without properly validating the target path. By creating a symbolic link (symlink) pointing to a critical system file (e.g., C:\Windows\System32\config\SAM or a privileged executable), an attacker can trick the installer into deleting that file instead of the intended temporary file.

Attack Flow:

1. Attacker gains low-privileged code execution on the target (e.g., via a malicious script or downloaded executable).
2. Attacker identifies a predictable temporary file path used by the Chroma SDK installer during its operation.
3. Attacker creates a symbolic link at that path, pointing to a target file they wish to delete (e.g., a system binary or a file owned by SYSTEM).
4. The installer runs (either triggered by the attacker or scheduled) and attempts to delete the temporary file.
5. Due to the symlink, the installer deletes the target file instead.
6. The attacker can then exploit the deletion to achieve privilege escalation (e.g., by replacing a deleted system binary with a malicious one, or by causing a service to fail and then injecting code).

The specific flaw is a classic "Untrusted Search Path" or "Link Following" vulnerability (CWE-59). The installer does not verify that the file being deleted is the intended one, nor does it check for symbolic links.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerable behavior can be described:

Vulnerable Code (Conceptual):

// Pseudo-code of vulnerable installer
void DeleteTempFile() {
    std::string tempPath = GetTempPath() + "\\RazerChromaTemp.tmp";
    // No check for symlink or file type
    DeleteFile(tempPath.c_str());
}

Patched Code (Expected):

// Pseudo-code of patched installer
void DeleteTempFile() {
    std::string tempPath = GetTempPath() + "\\RazerChromaTemp.tmp";
    // Check if the path is a symbolic link
    if (IsSymlink(tempPath.c_str())) {
        // Log error and abort
        LogError("Symlink detected, aborting deletion.");
        return;
    }
    // Verify the file is the expected temporary file
    if (!IsExpectedFile(tempPath.c_str())) {
        LogError("Unexpected file, aborting deletion.");
        return;
    }
    DeleteFile(tempPath.c_str());
}

The patched version would include checks to ensure the file being deleted is not a symlink and matches expected attributes (e.g., size, hash, or location).

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Windows 10/11 system with Razer Synapse 3 installed.
• Ability to execute low-privileged code (e.g., via a user-level account or a dropped executable).
• Knowledge of the temporary file path used by the Chroma SDK installer (e.g., C:\Users\<user>\AppData\Local\Temp\RazerChromaTemp.tmp).

Exploitation Steps:

1. Identify Target: Choose a file to delete that will lead to privilege escalation. Common targets include:
   • C:\Windows\System32\sethc.exe (Sticky Keys backdoor)
   • C:\Windows\System32\utilman.exe (Ease of Access backdoor)
   • A DLL loaded by a SYSTEM service.
2. Create Symlink: Use mklink or the CreateSymbolicLink API to create a symlink at the temporary path pointing to the target.

   mklink C:\Users\victim\AppData\Local\Temp\RazerChromaTemp.tmp C:\Windows\System32\sethc.exe
   

3. Trigger Installer: Run the Razer Chroma SDK installer (e.g., RazerChromaInstaller.exe). This can be done by launching Razer Synapse 3 or directly executing the installer.
4. Exploit Deletion: The installer deletes the target file via the symlink.
5. Escalate Privileges: Replace the deleted file with a malicious binary (e.g., a copy of cmd.exe renamed to sethc.exe). Then, at the login screen, press Shift five times to launch the malicious binary as SYSTEM.

Note: No public exploit code is available. The above is a theoretical exploitation path based on the vulnerability description.

Blue Team (Detection & Prevention)

Detection:

• Monitor for creation of symbolic links by non-administrator users, especially in temporary directories.
• Alert on file deletion operations by Razer Chroma SDK installer that target files outside the expected temporary directory.
• Use Sysmon Event ID 1 (Process Creation) to detect execution of mklink or CreateSymbolicLink API calls.
• Monitor for unusual file deletions in system directories (e.g., C:\Windows\System32).

Prevention:

• Apply the principle of least privilege: restrict user ability to create symbolic links (requires SeCreateSymbolicLinkPrivilege, which is typically only for administrators).
• Use Windows Defender Exploit Guard to block symbolic link creation from untrusted processes.
• Implement application whitelisting to prevent unauthorized executables from running.
• Keep Razer Synapse 3 updated; apply patches as soon as they become available.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2025_9871_Razer_Chroma_Symlink {
    meta:
        description = "Detects potential exploitation of CVE-2025-9871 via symlink creation in Razer Chroma SDK installer"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-9871"
    strings:
        $s1 = "RazerChromaInstaller.exe" nocase
        $s2 = "CreateSymbolicLink" nocase
        $s3 = "\\AppData\\Local\\Temp\\Razer" nocase
        $s4 = "\\Windows\\System32\\" nocase
    condition:
        (uint16(0) == 0x5A4D) and  // PE file
        all of ($s1, $s2, $s3) and
        $s4
}

Sigma Rule

title: CVE-2025-9871 - Razer Chroma SDK Symlink Exploitation
id: 8a7b3c2d-1e5f-4a6b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects creation of symbolic links by Razer Chroma SDK installer targeting system directories
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-9871
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\\RazerChromaInstaller.exe'
        CommandLine|contains: 'CreateSymbolicLink'
    condition: selection
falsepositives:
    - Legitimate Razer updates (rare)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"CVE-2025-9871 - Razer Chroma SDK Installer Download"; flow:to_server,established; content:"RazerChromaInstaller.exe"; http_uri; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Razer Chroma SDK Installer: If not needed, uninstall Razer Synapse 3 or disable the Chroma SDK component.
2. Restrict Symlink Creation: Ensure only administrators have the SeCreateSymbolicLinkPrivilege. Use Group Policy to remove this privilege from standard users.
3. Monitor for Exploitation: Deploy the YARA and Sigma rules above to detect potential exploitation attempts.

Long-Term Fix:

• Razer must release a patched version of the Chroma SDK installer that validates file paths and prevents symlink following. Until then, users should consider using alternative gaming peripheral software or running Razer Synapse 3 in a sandboxed environment.

Workaround:

• Use Windows Defender Application Control (WDAC) to block execution of RazerChromaInstaller.exe from untrusted locations.
• Implement file system auditing on C:\Windows\System32 to detect unauthorized deletions.

Valters IT