Description

Concurrent execution using shared resource with improper synchronization ('race condition') in Copilot Chat (Microsoft Edge) allows an authorized attacker to disclose information over a network.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.4",
  "pubDate": "2026-08-28T20:18:44.927Z",
  "pubdate": "2026-08-28T20:18:44.927Z",
  "executiveSummary": "A race condition vulnerability exists within the Copilot Chat feature integrated into Microsoft Edge, resulting from improper synchronization during concurrent execution processes. This flaw allows an authorized attacker to exploit timing discrepancies to facilitate unauthorized information disclosure over a network.\nThe vulnerability is categorized as a CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization). By leveraging the race condition, an attacker with local access or network proximity—depending on the specific architectural invocation of the chat component—can potentially access sensitive data that should be protected by synchronization primitives.\nThe risk implication is significant as it undermines the integrity of session data and privacy controls within the browser's assistant interface. An attacker capable of inducing the race condition can intercept or view information intended for the authenticated user session. Exploitation requires precise timing, but given the asynchronous nature of web-based LLM integrations, the attack surface remains viable for actors capable of manipulating concurrent requests or event loops.\nThis vulnerability highlights a failure in the thread-safety mechanisms governing resource shared between the browser process and the Copilot service, necessitating immediate attention to process isolation and atomic transaction handling.",
  "technicalDetails": "The core of the vulnerability resides in the improper management of shared resources during asynchronous operations within the Copilot Chat interface in Microsoft Edge. Specifically, the implementation fails to implement adequate locking mechanisms or atomic operations when handling concurrent requests to shared memory or state buffers.\nThe root cause is a classic 'Time-of-Check to Time-of-Use' (TOCTOU) conflict or a race condition where multiple threads or event-driven tasks contend for the same object state. When the Copilot Chat process handles information retrieval or processing, the lack of synchronization primitives allows for the modification or interception of data while the state is in a transient, inconsistent, or unprotected phase.\nThe exploitation flow typically begins with an attacker triggering high-frequency, concurrent requests that force the browser's internal chat handler to access shared resources simultaneously. By sending malformed or overlapping execution packets, the attacker forces a context switch or thread contention at a critical point in the data retrieval lifecycle. If successful, the race condition allows the attacker to read data from a buffer or cache that has not yet been cleared, sanitized, or properly scoped to the current user's session.\nFrom a technical perspective, this involves the manipulation of the internal communication channel between the Microsoft Edge process and the Copilot service endpoint. Because the chat interface relies on real-time data streaming and asynchronous callbacks, the race condition can be exploited to 'bleed' information across logical isolation boundaries. This could involve an attacker observing partial data streams intended for concurrent processes or accessing stale data residues left in shared memory buffers after a context switch occurs before the completion of an atomic operation.\nPost-exploitation impact involves the unauthorized disclosure of information which may include cached session tokens, user-specific prompt data, or contextual metadata transmitted during the chat session. Because this occurs via a race condition, the behavior is often non-deterministic, making it a stealthy vector for data exfiltration. The vulnerability requires no escalated privileges beyond those already authorized for the user, as the exploit leverages the existing, albeit poorly synchronized, execution path inherent to the browser's integration with the Copilot back-end."
}