CVE-2026-66314 in Edge
Summary
by MITRE • 08/04/2026
Time-of-check time-of-use (toctou) race condition in Microsoft Edge (Chromium-based) allows an unauthorized attacker to disclose information over a network.
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Analysis
by VulDB Data Team • 08/04/2026
A time-of-check time-of-use race condition vulnerability exists in Microsoft Edge browsers based on the Chromium engine, creating a critical security flaw that enables unauthorized attackers to potentially disclose sensitive information across network boundaries. This vulnerability stems from a fundamental timing issue where the system performs a check operation at one moment and then executes a use operation at a subsequent moment, with an opportunity for malicious interference between these two points. The race condition occurs when an attacker can manipulate the state of a resource between the moment when access permissions are verified and when the resource is actually accessed or modified. In the context of Microsoft Edge, this flaw manifests during network-based operations where the browser's handling of resources and their accessibility can be exploited through carefully timed attacks.
The technical implementation of this vulnerability involves the browser's failure to maintain consistent state validation throughout the resource access lifecycle. When Microsoft Edge processes network requests or handles file operations, it performs initial permission checks before executing actual resource access. An attacker can exploit this temporal gap by modifying the target resource or its access permissions between the check and use phases, potentially gaining access to resources that should otherwise be restricted. This type of vulnerability is classified as a race condition under the Common Weakness Enumeration framework with CWE-367, specifically categorized as a time-of-check to time-of-use flaw. The underlying issue often involves improper synchronization mechanisms or insufficient state validation between security checks and actual resource operations.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable more sophisticated attacks including privilege escalation, data exfiltration, and potential system compromise. Network-based attackers can leverage this weakness to access restricted files, network resources, or sensitive data that should be protected by the browser's security model. The attack vector typically involves an attacker controlling a remote server or having the ability to manipulate network traffic in a way that allows them to observe or modify resource states during the critical timing window. This creates opportunities for attackers to bypass access controls and gain unauthorized visibility into system resources, potentially leading to comprehensive information leakage across network boundaries.
Mitigation strategies for this vulnerability require immediate patching of affected Microsoft Edge versions through official updates from Microsoft, as the primary fix involves correcting the race condition in the browser's resource handling mechanisms. Organizations should implement network monitoring solutions to detect unusual access patterns that might indicate exploitation attempts, while also maintaining up-to-date security patches across all browser installations. The remediation process includes strengthening synchronization mechanisms within the browser's codebase and ensuring proper state validation throughout the resource access lifecycle. Security practitioners should consider implementing additional network segmentation and access control measures as defensive layers, while also monitoring for potential exploitation attempts through behavioral analytics that can detect anomalous timing patterns in network communications. This vulnerability aligns with attack techniques documented in the MITRE ATT&CK framework under the T1071.004 sub-technique for application layer protocol usage and T1566 for credential access through social engineering, as attackers may combine this flaw with other exploitation methods to achieve broader system compromise.