CVE-2024-26239 is a high-severity heap-based buffer overflow vulnerability identified in the Windows Telephony Server component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This vulnerability is classified under CWE-122, indicating a heap-based buffer overflow condition. The flaw arises when the Telephony Server improperly handles memory operations, allowing an attacker with limited privileges (PR:L) to execute a crafted request that causes a buffer overflow on the heap. This overflow can lead to arbitrary code execution with elevated privileges, compromising system confidentiality, integrity, and availability. The vulnerability does not require user interaction (UI:N) and has a low attack complexity (AC:L), but it requires local access (AV:L), meaning the attacker must have some form of local access or foothold on the affected system. The scope of impact is unchanged (S:U), but the consequences are severe, with high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no known exploits are currently reported in the wild, the vulnerability’s characteristics make it a significant risk, especially in environments where Windows 10 Version 1809 remains in use. The absence of published patches at the time of disclosure increases the urgency for mitigation. The Telephony Server is a critical system component that manages telephony-related services, and exploitation could allow attackers to escalate privileges from a limited user context to SYSTEM-level control, enabling full system compromise.

For European organizations, the impact of CVE-2024-26239 could be substantial, particularly in sectors relying on legacy Windows 10 Version 1809 systems, such as manufacturing, healthcare, and government agencies. Successful exploitation could allow attackers to gain elevated privileges, bypass security controls, and deploy further malware or ransomware, potentially disrupting critical services and causing data breaches. The high impact on confidentiality, integrity, and availability means sensitive personal data protected under GDPR could be exposed or altered, leading to regulatory penalties and reputational damage. Additionally, the local access requirement suggests that insider threats or attackers who have already compromised lower-privileged accounts could leverage this vulnerability to escalate privileges and move laterally within networks. The lack of user interaction needed facilitates automated exploitation once local access is obtained, increasing the risk in environments with weak endpoint security or insufficient network segmentation. Organizations with remote or hybrid workforces using outdated Windows 10 versions may face increased exposure if devices are not adequately managed or updated.

1. Immediate prioritization of upgrading or patching affected Windows 10 Version 1809 systems as soon as Microsoft releases an official patch. 2. Implement strict local access controls and limit user privileges to the minimum necessary to reduce the risk of privilege escalation. 3. Employ application whitelisting and endpoint detection and response (EDR) solutions to monitor and block suspicious behavior related to Telephony Server processes. 4. Conduct network segmentation to isolate legacy systems and restrict lateral movement opportunities for attackers. 5. Regularly audit and remove unnecessary telephony services or components if not required in the environment to reduce the attack surface. 6. Enforce strong authentication and endpoint security policies, including disabling or restricting local administrative accounts and enforcing multi-factor authentication for sensitive access. 7. Monitor system logs and telemetry for anomalous activity indicative of exploitation attempts, focusing on Telephony Server and related service behaviors. 8. Educate IT and security teams about the vulnerability specifics to ensure rapid response and containment if exploitation is suspected.