CVE-2025-21171 is a high-severity heap-based buffer overflow vulnerability (CWE-122) identified in Microsoft PowerShell version 7.5.0. This vulnerability allows remote attackers to execute arbitrary code on affected systems by exploiting improper handling of memory buffers within PowerShell's .NET runtime environment. Specifically, the flaw arises when PowerShell processes certain inputs or commands that cause it to write beyond the allocated heap memory boundaries, leading to memory corruption. This corruption can be leveraged to execute remote code with the privileges of the user running PowerShell. The vulnerability is remotely exploitable over the network without requiring prior authentication, but it does require user interaction, such as running a crafted PowerShell script or command. The CVSS v3.1 base score is 7.5, reflecting high severity due to its impact on confidentiality, integrity, and availability. Although no known exploits are currently reported in the wild, the vulnerability's nature and the widespread use of PowerShell make it a significant risk. No official patches or mitigations have been published yet, indicating that organizations must be vigilant and prepare for upcoming updates. The vulnerability affects PowerShell 7.5.0 specifically, which is a cross-platform automation and scripting tool widely used in enterprise environments for system administration and automation tasks.

For European organizations, this vulnerability poses a substantial risk due to the extensive use of PowerShell in IT infrastructure management, automation, and cloud environments. Successful exploitation could lead to full system compromise, allowing attackers to steal sensitive data, disrupt services, or move laterally within networks. This is particularly critical for sectors with stringent data protection requirements such as finance, healthcare, and government institutions across Europe. The ability to execute remote code without authentication but requiring user interaction means phishing or social engineering campaigns could be effective attack vectors. Additionally, the cross-platform nature of PowerShell 7.5 means that both Windows and non-Windows systems in European enterprises could be affected, increasing the attack surface. The potential for widespread disruption and data breaches could also have regulatory implications under GDPR and other European data protection laws.

Given the absence of an official patch at the time of this report, European organizations should implement immediate compensating controls. These include restricting PowerShell usage to trusted administrators and limiting script execution policies to signed scripts only. Network-level controls such as firewall rules should block unsolicited inbound traffic to systems running PowerShell 7.5, especially from untrusted networks. Employ endpoint detection and response (EDR) solutions to monitor for anomalous PowerShell activity, including unusual script executions or memory usage patterns indicative of exploitation attempts. User awareness training should emphasize the risks of executing unsolicited scripts or commands received via email or other communication channels. Organizations should also inventory and identify all instances of PowerShell 7.5.0 deployment across their environments to prioritize mitigation efforts. Once Microsoft releases a patch, rapid deployment is critical. Additionally, consider implementing application whitelisting and privilege restrictions to limit the impact of potential exploitation.