CVE-2025-15595 is a vulnerability identified in mlsoft's Inno Setup software, specifically versions 6.2.1 and earlier. The issue is categorized under CWE-1390, which relates to weak authentication mechanisms. The vulnerability manifests as a privilege escalation vector through DLL hijacking. Inno Setup, a widely used installer creation tool, loads DLLs during the installation process. Due to insufficient validation or authentication of these DLLs, a local attacker with limited privileges can place a malicious DLL in a location where the installer loads it instead of the legitimate one. This hijacking allows the attacker to execute arbitrary code with elevated privileges, potentially gaining administrative rights on the affected system. The CVSS 4.0 vector indicates that exploitation requires local access (AV:L), high attack complexity (AC:H), and privileges at a low level (PR:L), but no user interaction (UI:N). The vulnerability impacts confidentiality, integrity, and availability at a high level (VC:H, VI:H, VA:N), and the scope is high (SC:H), meaning it can affect resources beyond the initially compromised component. No patches or exploits are currently publicly available, but the vulnerability is officially published and reserved by NCSC-FI. The lack of user interaction and the potential for privilege escalation make this a significant concern for environments where Inno Setup is used to deploy software, especially in enterprise settings.

The primary impact of CVE-2025-15595 is unauthorized privilege escalation, which can lead to full system compromise. An attacker who gains local access with limited privileges can exploit this vulnerability to execute code with elevated rights, potentially installing persistent malware, altering system configurations, or accessing sensitive data. This undermines the confidentiality, integrity, and availability of affected systems. Organizations relying on Inno Setup for software deployment risk having their installation processes subverted, which could lead to widespread compromise if attackers insert malicious payloads during software installation. The vulnerability's high scope impact means that the compromise can extend beyond the installer process to other system components. Although exploitation requires local access and is complex, insider threats or attackers who have already breached perimeter defenses could leverage this vulnerability to escalate privileges and move laterally within networks. This risk is particularly critical in environments with strict privilege separation and sensitive data, such as financial institutions, government agencies, and critical infrastructure providers.

To mitigate CVE-2025-15595, organizations should first monitor for and apply any official patches or updates released by mlsoft for Inno Setup. In the absence of patches, administrators should enforce strict DLL loading policies by configuring system-wide or application-specific DLL search order to prevent loading of unauthorized DLLs. This can include using Windows features such as SafeDllSearchMode and setting explicit DLL paths. Employing application whitelisting and code integrity policies (e.g., Microsoft AppLocker or Windows Defender Application Control) can prevent execution of untrusted DLLs. Additionally, restricting write permissions on directories where DLLs are loaded or placed can reduce the risk of DLL hijacking. Security teams should audit and monitor installer execution environments for anomalous DLL loads or unexpected privilege escalations. Educating developers and deployment teams about secure installer practices and avoiding running installers with unnecessary elevated privileges can further reduce risk. Finally, implementing endpoint detection and response (EDR) solutions capable of detecting suspicious DLL injection or hijacking behaviors will enhance detection and response capabilities.