Description

Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Telephony Service allows an authorized attacker to elevate privileges locally.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.0",
  "pubDate": "2026-08-11T17:18:27.050Z",
  "pubdate": "2026-08-11T17:18:27.050Z",
  "executiveSummary": "A local privilege escalation vulnerability exists within the Windows Telephony Service, specifically categorized as a concurrent execution using shared resource with improper synchronization or race condition flaw.\nThis vulnerability impacts the Windows Telephony Service component, allowing an authorized local attacker to manipulate shared system resources during concurrent operations.\nSuccessful exploitation of this security defect permits a threat actor to elevate their execution privileges locally on the targeted operating system.\nThe primary risk implication involves unauthorized vertical privilege escalation, potentially granting the attacker elevated access rights such as SYSTEM or administrator-level capabilities.\nExploitation requirements dictate that the attacker must already possess local access to the system and be authorized to interact with the telephony subsystem.\nBecause the flaw relies on timing-dependent race conditions, successful exploitation requires precise synchronization of concurrent execution threads against the shared resource managed by the vulnerable service.",
  "technicalDetails": "The vulnerability resides in the Windows Telephony Service, which improperly synchronizes access to shared resources during concurrent execution threads.\nThe root cause is a classic race condition (CWE-362) where multiple threads access and modify critical system state variables or memory structures without adequate mutual exclusion primitives, such as mutexes or critical sections.\nAn authorized local attacker can exploit this flaw by spawning concurrent processes or threads designed to interact with the Windows Telephony Service API.\nBy timing these requests precisely, the attacker intercepts or alters the state of shared resources during the critical window between validation and actual usage (TOCTOU - Time-of-Check to Time-of-Use).\nThis improper synchronization allows the attacker to corrupt memory structures, manipulate object handles, or induce unintended state transitions within the privileged service context.\nAuthentication requirements are limited to local execution, meaning the attacker must possess valid credentials or code execution capability on the local machine.\nPrivilege requirements are low regarding initial access, as the attacker leverages authorized local execution to target the higher-privileged telephony service process.\nNetwork exposure is non-existent, as the vulnerability is strictly local and cannot be triggered remotely over a network protocol.\nStep-by-step exploitation involves initiating a high-frequency stream of specific telephony service requests while simultaneously executing a secondary payload thread that monitors and races for the targeted shared resource.\nWhen the race condition is successfully won, the service executes operations on attacker-controlled or manipulated data structures.\nThe post-exploitation impact includes local privilege escalation, enabling the execution of arbitrary code with the elevated security context of the Windows Telephony Service."
}