CVE-2026-21523 in Visual Studio Code
Summary
by MITRE • 02/10/2026
Time-of-check time-of-use (toctou) race condition in GitHub Copilot and Visual Studio allows an authorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 02/13/2026
The vulnerability identified as CVE-2026-21523 represents a critical time-of-check time-of-use race condition affecting GitHub Copilot and Visual Studio environments. This flaw exploits a fundamental timing issue where the system performs a security check at one moment and subsequently accesses resources at a different moment, creating an exploitable window where malicious actors can manipulate the system state between these operations. The vulnerability specifically impacts the integrated development environment ecosystem where code completion and AI-assisted programming features are utilized, making it particularly dangerous in development workflows where trust and automation are paramount.
The technical implementation of this race condition occurs within the code execution and file access mechanisms of the Copilot extension and Visual Studio integration. When a user initiates certain code operations or file manipulations, the system performs a permission check or validation before proceeding with the actual resource access. However, during this brief temporal gap, an attacker with authorized access can modify or replace the targeted files, directories, or code resources, effectively bypassing the initial security validation. This allows for arbitrary code execution through network-based attacks, as the compromised system components can be leveraged to establish remote access or execute malicious payloads. The vulnerability aligns with CWE-367, which specifically addresses time-of-check to time-of-use flaws, and represents a classic example of how temporal inconsistencies in security validation can be exploited.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a pathway for persistent network-based code execution within development environments. Attackers can exploit this weakness to inject malicious code into development workflows, potentially compromising entire development pipelines, source code repositories, and integrated development environments. The implications are particularly severe in enterprise settings where Visual Studio and GitHub Copilot are widely deployed for collaborative software development. The vulnerability can be leveraged to establish backdoors, exfiltrate sensitive source code, or manipulate development processes, making it a significant concern for organizations that rely heavily on these tools for their software development lifecycle. This type of vulnerability directly maps to ATT&CK technique T1059, which covers command and scripting interpreter, and T1566, which addresses credential access through network-based attacks.
Mitigation strategies for CVE-2026-21523 must address both the immediate race condition vulnerability and broader security posture improvements. Organizations should implement immediate patch management protocols to ensure all instances of GitHub Copilot and Visual Studio are updated with the latest security fixes. Additionally, security controls should include enhanced file access monitoring, implementing atomic operations where checks and uses occur simultaneously, and reducing the temporal window between validation and execution. Network segmentation and access controls should be reinforced to limit the potential damage from successful exploitation, while monitoring systems should be enhanced to detect anomalous file access patterns or unauthorized modifications. The implementation of secure coding practices and regular security assessments of integrated development environments will help prevent similar vulnerabilities from emerging in future releases of these critical development tools.