BSI warns of critical security gap in Windows

The youngest Windows patch fixes a zero-day gap that was probably actively exploited.

Microsoft has confirmed and closed a critical zero-day security gap in Windows (CVE-2025-30397), which is currently being actively exploited by attackers. This weak point affects all supported Windows versions and enables attackers to carry out malicious code via the network under certain conditions, which can lead to complete control over affected systems.

The weak point was communicated by the Microsoft Security Response Center (MSRC); The associated security updates were published as part of May 2025 Patch Tuesday.

The Federal Office of Safety in Information Technology (BSI) has published an urgent warning accordingly and recommends the immediate installation of the available updates.

The as CVE-2025-30397 Registered weakness is classified as a “Type Confusion Vulnerability” in the Microsoft Scripting Engine.

With this type of security gap, resources are processed with incompatible types, which can lead to unpredictable behavior and ultimately to execute maliccode. After the Common Vulnerability Scoring System (CVSS), the weak point was rated with a value of 7.5 on a scale of 1 to 10, which classifies it as a “high risk”.

• For a successful use of the security gap, the target system Microsoft Edge must run in Internet Explorer mode, and the user must click on a specially prepared URL.
• This may initially restrict the danger somewhat, but in corporate environments, where Internet Explorer mode for compatibility with older web applications is still often used, this is a significant risk.