CVE-2025-21302 is a high-severity heap-based buffer overflow vulnerability (CWE-122) affecting the Windows Telephony Service on Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This vulnerability allows remote code execution (RCE) without requiring authentication (AV:N/PR:N), but does require user interaction (UI:R), such as the user answering or interacting with a telephony-related prompt. The flaw exists due to improper handling of memory buffers in the Telephony Service, which could be exploited by an attacker sending specially crafted network packets or telephony requests to a vulnerable system. Successful exploitation could allow an attacker to execute arbitrary code with system-level privileges, leading to full system compromise. The CVSS v3.1 base score is 8.8, indicating a high impact on confidentiality, integrity, and availability (all rated high). The vulnerability is exploitable over the network with low attack complexity and no privileges required, but user interaction is necessary. No known exploits are currently reported in the wild, and no official patches or mitigation links have been published yet. Given the affected product is Windows 10 Version 1809, which is an older but still in-use version, many enterprise and government systems may remain vulnerable if not updated or mitigated. The Telephony Service is a core Windows component used for managing telephony and VoIP functions, so exploitation could disrupt communications and enable persistent footholds for attackers.

For European organizations, this vulnerability poses a significant risk, especially for sectors relying on legacy Windows 10 Version 1809 systems, including government agencies, healthcare, finance, and critical infrastructure. Exploitation could lead to unauthorized access to sensitive data, disruption of telephony and communication services, and potential lateral movement within networks. The ability to execute code remotely with system privileges could allow attackers to deploy ransomware, spyware, or other malware, severely impacting business continuity and data confidentiality. Since the vulnerability requires user interaction, phishing or social engineering campaigns targeting employees could facilitate exploitation. The lack of an available patch increases the window of exposure, making proactive mitigation essential. Organizations with remote or hybrid workforces using vulnerable systems are particularly at risk due to increased network exposure.

1. Immediate mitigation should focus on minimizing exposure of Windows 10 Version 1809 systems to untrusted networks, including restricting inbound telephony-related network traffic via firewalls and network segmentation. 2. Disable or restrict the Windows Telephony Service on systems where it is not required, using Group Policy or service configuration to reduce the attack surface. 3. Implement strict user awareness training to reduce the risk of social engineering or phishing attacks that could trigger the required user interaction for exploitation. 4. Monitor network traffic and system logs for unusual telephony service activity or signs of exploitation attempts. 5. Prioritize upgrading affected systems to a supported and patched Windows version as soon as possible, since no official patches are currently available. 6. Employ endpoint detection and response (EDR) solutions capable of detecting anomalous behavior related to memory corruption or remote code execution attempts. 7. Maintain regular backups and incident response plans to quickly recover from potential compromises.