This vulnerability is a TOCTOU race condition (CWE-367) in the Microsoft Visual Studio Code CoPilot Chat Extension (version 0.27.0). It allows an attacker with authorized access to execute arbitrary code remotely by exploiting the timing window between checking a condition and using the checked resource. The CVSS v3.1 base score is 8.0, indicating high severity with network attack vector, low attack complexity, required privileges, and user interaction. Microsoft has published an official fix for this vulnerability.

Successful exploitation of this vulnerability can lead to remote code execution with high impact on confidentiality, integrity, and availability. An attacker with authorized access can leverage this race condition to run arbitrary code over the network, potentially compromising the affected system. No known exploits are currently reported in the wild.

An official fix is available from Microsoft. Users of the Microsoft Visual Studio Code CoPilot Chat Extension version 0.27.0 should apply the vendor-provided patch immediately to remediate this vulnerability. Refer to the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21523 for detailed update instructions.