CVE-2026-55945: Microsoft Edge Race Condition Information Disclosure Vulnerability

Technical summary

CVE-2026-55945 is a race condition vulnerability (CWE-362) in Microsoft Edge's Chromium engine affecting concurrent execution and shared resource access. The flaw permits an authorized local attacker to read information from memory or storage that should be restricted. The attack requires local access, elevated privilege context (PR:L), and precise timing or conditions to succeed (AC:H). The vulnerability does not enable code execution or system availability attacks, but can result in confidentiality and integrity impacts through information disclosure and potential state manipulation.

Business impact

This vulnerability primarily threatens confidentiality in environments where multiple local users share Edge instances or where sensitive data is processed within Edge's memory space. Organizations with shared workstations, terminal servers, or multi-tenant systems face elevated risk if authorized users can coordinate or exploit timing windows. The impact is localized to information disclosure rather than lateral movement or persistent compromise, reducing—but not eliminating—enterprise-wide risk. Affected data could include cached credentials, authentication tokens, or user session information depending on what Edge holds in the vulnerable shared resource.

Affected systems

Microsoft Edge based on Chromium is affected. Organizations running Edge on Windows, macOS, or Linux systems should assess their deployment footprint. The vulnerability requires local user access, so air-gapped or single-user desktop environments face lower risk than shared lab systems, thin-client deployments, or remote desktop infrastructure where multiple authorized users operate simultaneously.

Exploitability

Exploitability is limited by several factors: an attacker must possess local user credentials (PR:L), the attack has high complexity (AC:H) requiring precise timing or specific conditions, and no user interaction is needed once those preconditions are met (UI:N). Public exploitation is unlikely unless the race condition window and specific resource access pattern are widely documented. The vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog, suggesting no active exploitation in the wild at publication date. However, once technical details are disclosed, motivated threat actors with local access could develop reliable exploits.

Remediation

Apply the latest security updates from Microsoft for Edge. Microsoft typically addresses Chromium-based vulnerabilities through the regular Edge update cycle. Check Microsoft Edge's settings (Help > About Microsoft Edge) to ensure automatic updates are enabled, or manually update to the latest version. Verify the patch version against Microsoft's security advisory for CVE-2026-55945 to confirm the fix is included. Organizations should also review shared system configurations and restrict unnecessary local user privileges to reduce the attack surface.

Patch guidance

Enable automatic updates for Microsoft Edge to receive fixes as they roll out. If your organization uses managed Edge deployments, verify that the latest security update containing the race condition fix has been pushed to your fleet. Manually verify updates by navigating to Help > About Microsoft Edge; the browser will display the current version and check for updates automatically. Test the updated version in a non-production environment before broad rollout, particularly if your organization uses Edge extensions or has custom configurations. Verify against the official Microsoft security advisory to confirm the specific build version that resolves CVE-2026-55945.

Detection guidance

Detection of exploitation in the wild is challenging because race conditions typically leave minimal forensic evidence. Monitor for suspicious multi-process or multi-thread activity involving Edge, particularly in shared system environments. Log and alert on unauthorized local privilege escalation attempts preceding potential exploitation. Use security information and event management (SIEM) tools to correlate rapid Edge memory access patterns or resource contention events if available through OS-level instrumentation. Implement kernel-level tracing or user-space monitoring on high-value systems to detect timing-based attacks targeting Edge's shared resources, though this approach requires significant tuning to avoid false positives.

Why prioritize this

While the CVSS score of 4.2 reflects low severity, this vulnerability warrants timely patching in shared or multi-user environments. The risk of information disclosure affecting credentials or session data justifies standard patch management cycles. Organizations should prioritize patching based on deployment context: remote desktop or shared workstation environments should receive updates first, followed by general desktop fleets. Single-user or air-gapped systems can follow normal update schedules without urgency.

Risk score, explained

The CVSS 3.1 score of 4.2 (MEDIUM severity) reflects the limited attack surface: local access requirement (AV:L), high complexity (AC:H), and low privilege level (PR:L) constrain real-world exploitation. The confidentiality (C:L) and integrity (I:L) impacts are partial rather than complete, and there is no availability impact (A:N). The scope is changed (S:C), meaning the vulnerability can affect resources beyond the vulnerable component. Overall, this is a moderate-risk flaw requiring patching but not an emergency requiring emergency out-of-band releases or immediate workarounds.

Frequently asked questions