Windows Telephony Service — CraftedSignal Threat Feed

CVE-2026-42825: Use-After-Free in Windows Telephony Service

hello@craftedsignal.io — Tue, 12 May 2026 18:53:18 +0000

CVE-2026-42825 is a use-after-free vulnerability affecting the Windows Telephony Service. This vulnerability allows an attacker with local access and low privileges to potentially elevate their privileges on the system. The vulnerability arises from improper memory management within the Telephony Service, leading to a situation where a freed memory region is accessed again. Successful exploitation could lead to arbitrary code execution with elevated privileges. Microsoft has acknowledged this vulnerability and assigned it a CVSS v3.1 score of 7.0, indicating a high severity. Defenders should monitor for unusual activity related to the Telephony Service and prioritize patching to mitigate this risk.

Attack Chain

Attacker gains initial local access to the target system with low privileges.
Attacker identifies the Windows Telephony Service running on the system.
Attacker crafts a specific input that triggers the use-after-free condition in the Telephony Service.
The malicious input causes the Telephony Service to free a memory region.
The attacker then causes the Telephony Service to access the freed memory region.
This memory access allows the attacker to overwrite critical system data or inject malicious code.
The injected code is executed with the privileges of the Telephony Service, leading to privilege elevation.
Attacker leverages elevated privileges to perform unauthorized actions on the system.

Impact

Successful exploitation of CVE-2026-42825 allows a local attacker to escalate their privileges on a vulnerable Windows system. This could allow the attacker to gain complete control over the system, install malware, access sensitive data, or disrupt critical services. Given the potential for complete system compromise, organizations should prioritize patching this vulnerability.

Recommendation

Apply the patch released by Microsoft to address CVE-2026-42825 on all affected systems.
Enable Sysmon process creation logging to monitor for unusual processes spawned by the Telephony Service, facilitating the detection of potential exploitation attempts via the Sigma rules provided.
Monitor for unexpected modifications to system files or registry keys by the Telephony Service, using endpoint detection and response (EDR) solutions.
Deploy the Sigma rules in this brief to your SIEM and tune for your environment.

CVE-2026-40382 - Windows Telephony Service Use-After-Free Elevation of Privilege

hello@craftedsignal.io — Tue, 12 May 2026 18:45:53 +0000

A use-after-free vulnerability, CVE-2026-40382, exists within the Windows Telephony Service. This flaw enables a locally authenticated attacker to gain elevated privileges on a vulnerable system. The vulnerability stems from improper memory management within the Telephony Service, allowing for the potential execution of arbitrary code with elevated permissions. Exploitation requires an attacker to have valid credentials on the target system. This vulnerability was reported to Microsoft and assigned a CVSS v3.1 base score of 7.8. Successful exploitation leads to a complete compromise of the affected system.

Attack Chain

An attacker gains initial access to the system with valid user credentials.
The attacker executes a specially crafted application or script that interacts with the Windows Telephony Service.
The crafted application triggers the use-after-free condition in the Telephony Service by improperly freeing a memory address.
The attacker then reallocates the freed memory address with attacker-controlled data.
The Telephony Service attempts to access the reallocated memory, now containing attacker-controlled data, leading to code execution.
The attacker executes arbitrary code with elevated privileges, such as SYSTEM.
The attacker installs malware, modifies system settings, or exfiltrates sensitive data.
The attacker maintains persistent access to the compromised system.

Impact

Successful exploitation of CVE-2026-40382 allows a local attacker to elevate their privileges to SYSTEM, granting them complete control over the compromised system. This can lead to data theft, system corruption, or the installation of malware. Given the nature of the vulnerability, any Windows system running the vulnerable Telephony Service is susceptible, potentially impacting a large number of users and organizations.

Recommendation

Apply the security update released by Microsoft to address CVE-2026-40382 as soon as possible (Reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40382).
Monitor for suspicious processes interacting with the Windows Telephony Service using the Sigma rule provided below to detect potential exploitation attempts.
Implement the provided Sigma rule to detect potential exploitation attempts through abnormal process creation events related to the Telephony Service.