CVE-2026-42906: Windows Shell Information Disclosure Vulnerability

Technical summary

This vulnerability stems from improper access controls in Windows Shell components, classified as CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N) indicates local attack vector, low attack complexity, requirement for low-level privileges, no user interaction needed, and high confidentiality impact while maintaining system integrity and availability. The flaw permits an authenticated local user to access protected information normally restricted from their privilege level, likely via improper permission checks or information leakage in shell data structures or outputs.

Business impact

Information disclosure vulnerabilities in OS core components can expose credentials, API keys, application data, or configuration secrets that may be stored in memory or accessible through shell query mechanisms. Compromise of such data often leads to lateral movement, further system exploitation, or access to downstream applications and services. For organizations with shared workstations, terminal server environments, or remote access scenarios, this becomes a supply chain and insider-risk consideration.

Affected systems

The vulnerability affects multiple widely-deployed Windows versions: Windows 10 (versions 21H2 and 22H2), Windows 11 (versions 23H2, 24H2, 25H2, and 26H1), Windows Server 2022, and Windows Server 2025. The broad version coverage indicates this is a foundational Shell component issue affecting consumer, professional, and server deployments across recent release streams.

Exploitability

Exploitation requires local system access with valid user credentials—a genuine but common threat model, especially in office, shared computing, and remote access environments. An attacker cannot exploit this remotely or without authentication. The low attack complexity and lack of user interaction requirement mean that once local access is gained, the attack is straightforward and does not require social engineering or additional system misconfigurations. However, the prerequisite of prior compromise limits broad exploitation in well-controlled environments.

Remediation

Microsoft will address this vulnerability through security updates distributed via Windows Update and Windows Server Update Services. Organizations should apply patches across all affected versions when available. Until patches are deployed, compensating controls include restricting local logon privileges to trusted users only, disabling unnecessary local accounts, enforcing strong password policies to reduce credential compromise risk, and monitoring for unusual local account activity or shell query patterns.

Patch guidance

Monitor Microsoft's security update releases for patches addressing CVE-2026-42906 across Windows 10 21H2, Windows 10 22H2, Windows 11 (all current versions), Windows Server 2022, and Windows Server 2025. Verify patch applicability against your environment and deploy through your standard patch management process. Given the medium severity and local-only attack vector, coordinate patching with your change management schedule but prioritize systems in high-risk environments (shared workstations, terminal servers, multi-tenant platforms).

Detection guidance

Detection requires monitoring for atypical access patterns to sensitive Windows Shell data or registry locations that store protected information. Endpoint Detection and Response (EDR) tools should flag processes running with low privileges attempting to enumerate or access restricted system information. Audit local logon events and correlate with suspicious shell or system query activity. Organizations using Windows Advanced Threat Protection (ATP) or Defender for Endpoint should enable behavioral rules that detect reconnaissance or data exfiltration attempts from low-privilege contexts.

Why prioritize this

This vulnerability merits prompt but measured response. While the MEDIUM severity rating reflects limited exploitability (local-only requirement) and impact scope (confidentiality only), the breadth of affected versions and the foundational role of Windows Shell in system operation warrant systematic remediation planning. Priority should increase if your organization operates shared-access environments, terminal services, or high-value endpoints where insider threat or credential compromise is a realistic concern.

Risk score, explained

The CVSS 5.5 score reflects a balanced risk profile: high confidentiality impact and low attack complexity offset by strict local-access and authentication prerequisites. The score correctly positions this as a legitimate but contained threat—more serious than low-severity bugs but less critical than remote code execution or privilege escalation flaws. For most organizations with segregated user accounts and monitoring, the practical risk is below the numerical score; for shared-access or multi-tenant environments, risk may exceed the CVSS rating.

Frequently asked questions