CVE-2025-15595: Inno Setup Privilege Escalation Flaw

CVE-2025-15595 Overview

CVE-2025-15595 is a privilege escalation vulnerability affecting Inno Setup, a popular free installer creation tool for Windows programs. The vulnerability exists in Inno Setup version 6.2.1 and earlier versions, allowing attackers to exploit DLL hijacking to escalate privileges on the affected system.

Critical Impact

Attackers with local access can leverage DLL hijacking to escalate privileges, potentially gaining elevated access to execute malicious code with higher system permissions.

Affected Products

• Inno Setup version 6.2.1
• Inno Setup versions earlier than 6.2.1

Discovery Timeline

• 2026-03-03 - CVE-2025-15595 published to NVD
• 2026-03-03 - Last updated in NVD database

Technical Details for CVE-2025-15595

Vulnerability Analysis

This vulnerability is classified under CWE-1390 (Weak Authentication). The flaw enables privilege escalation through DLL hijacking, a technique where an attacker places a malicious Dynamic Link Library (DLL) in a location where the vulnerable application will load it instead of the legitimate library.

When Inno Setup or installers created with Inno Setup execute, they may search for required DLLs in directories that could be writable by unprivileged users. If an attacker can place a malicious DLL in one of these search paths before the legitimate DLL is loaded, the malicious code executes with the same privileges as the target application.

The attack requires local access to the system, along with specific conditions to be met regarding the DLL search order and write permissions to relevant directories. This complexity moderates the immediate risk but still presents a significant security concern in environments where Inno Setup-based installers are commonly used.

Root Cause

The root cause of this vulnerability lies in improper handling of the DLL search order during application execution. Inno Setup fails to adequately validate or restrict the paths from which it loads DLLs, allowing attackers to insert malicious libraries into the search path. This is a common weakness in Windows applications that do not implement secure DLL loading practices such as using absolute paths or SafeDllSearchMode configurations.

Attack Vector

The attack vector is local, requiring the attacker to have access to the target system. The exploitation process typically involves:

1. Identifying writable directories in the DLL search path used by Inno Setup
2. Crafting a malicious DLL with the same name as a legitimate library loaded by the application
3. Placing the malicious DLL in a location that will be searched before the legitimate DLL location
4. Waiting for or triggering execution of Inno Setup or an installer created with Inno Setup
5. The malicious DLL executes with the privileges of the target process

The attack requires specific preconditions to be met, including appropriate file system permissions and timing, which adds complexity to successful exploitation. However, in environments where installers run with elevated privileges, successful exploitation could result in complete system compromise.

Detection Methods for CVE-2025-15595

Indicators of Compromise

• Unexpected DLL files appearing in directories associated with Inno Setup installations or installer execution paths
• Unsigned or suspiciously signed DLL files in application directories that would normally contain only vendor-signed binaries
• Process execution logs showing Inno Setup processes loading DLLs from unexpected locations

Detection Strategies

• Monitor for file creation events in directories commonly used by Inno Setup installations
• Implement application allowlisting to prevent unauthorized DLLs from being loaded
• Use endpoint detection tools to alert on DLL sideloading attempts targeting known vulnerable applications
• Review process execution trees for abnormal parent-child relationships involving installer processes

Monitoring Recommendations

• Enable detailed Windows Event logging for process creation and DLL loading events
• Configure SIEM rules to detect suspicious DLL loading patterns associated with privilege escalation
• Implement file integrity monitoring on directories where Inno Setup components are installed

How to Mitigate CVE-2025-15595

Immediate Actions Required

• Update Inno Setup to the latest version that addresses this vulnerability
• Review and restrict write permissions on directories in the DLL search path
• Audit systems for any unauthorized DLL files in Inno Setup installation directories
• Consider using application control solutions to prevent unauthorized code execution

Patch Information

JR Software has released updated information regarding this vulnerability. Users should consult the JRSoftware Update Information for details on available fixes and version updates that address this DLL hijacking vulnerability.

Workarounds

• Restrict write access to directories in the system PATH and application installation directories
• Run Inno Setup and related installers from protected directories with limited user write access
• Implement strict application whitelisting policies to prevent unauthorized DLLs from executing
• Use User Account Control (UAC) and principle of least privilege to limit the impact of potential exploitation

# Example: Restrict write permissions on Inno Setup installation directory
# Run from an elevated command prompt
icacls "C:\Program Files (x86)\Inno Setup 6" /inheritance:r /grant:r "BUILTIN\Administrators:(OI)(CI)F" /grant:r "BUILTIN\Users:(OI)(CI)RX"