overview

CVE-2026-21510 is a Windows Shell security feature bypass vulnerability (CVSS 8.8, rated Important) that allows an unauthorized attacker to bypass protections like Windows SmartScreen and Shell security prompts over a network, potentially enabling code execution. Attackers exploit it by tricking users into clicking a malicious link or shortcut file, requiring one-click user interaction but no authentication.

Affected Products and Versions

  • Microsoft Windows Shell (specific versions not detailed in advisories; affects systems prior to the February 2026 Patch Tuesday update).

Microsoft released patches on February10, 2026, via the security update guide to address this issue.

Current Threat Status

This vulnerability has been exploited in the wild as a zero-day, with functional exploit techniques for phishing-based attacks bypassing SmartScreen via crafted links or shortcuts. No specific targeted industries are reported, but its one-click nature makes it highly attractive for broad campaigns; no public exploits are available, though pricing is estimated at $5k-$25k.

 

SUmmary

CVSS Score: 8.8 (High).
CVSS Vector String: Not currently provided or confirmed in search results.
KEV: Not listed in the CISA KEV catalog based on available data.
EPSS: Not provided in the search results.
CWE: Not currently provided or confirmed in search results (CWE-693 referenced in some analyses).

Compliance Impact (CVSS ≥ 7.0)

This vulnerability, a Windows Shell security feature bypass allowing unauthorized network access, has compliance implications due to its high severity and potential for bypassing protections:

  • PCI DSS: Violates requirements 6 (secure systems development) and 11 (regular testing), as it enables unauthorized access potentially exposing cardholder data.

  • HIPAA: Risks unauthorized access to systems handling Protected Health Information (PHI), violating 164.308(a)(1) administrative safeguards for access control.

  • SOX: Impacts internal controls over financial reporting by compromising system integrity and access restrictions (e.g., section 404).

  • ISO 27001: Breaches A.9 (access control) and A.12 (operations security) domains through failure of protection mechanisms.

  • NIST CSF: Affects "Protect" (PR.AC-1: Identity Management, PR.DS-5: Protection of Information) and "Detect" (DE.AE-1: Anomalies) functions.

 

Indicators of compromise (IOCs)

At this time, there are no known IOCs associated with successful exploitation of CVE-2026-21510. Avertium remains vigilant in locating IOCs for our customers and will disclose them as soon as possible.

For more information on how Avertium can help protect your organization, please reach out to your Avertium Service Delivery Manager or Account Executive.

 

mitre att&ck ttps

TTPs to Monitor

Defense Evasion

  • T1562 - Impair Defenses: The vulnerability enables bypassing Windows Shell security features, allowing attackers to evade detection or restriction mechanisms over a network.

  • T1222 - File and Directory Permissions Modification: Exploiting the protection mechanism failure in Windows Shell to alter security boundaries or bypass access controls.

Execution

  • T1203 - Exploitation for Client Execution: Attackers leverage the security feature bypass to execute unauthorized code or actions within the Windows Shell environment remotely.

Initial Access

  • T1190 - Exploit Public-Facing Application: Unauthorized network access through the bypassed Windows Shell security feature provides an initial foothold on the system.

  • No direct mappings or confirmed exploit details for CVE-2026-21510 were found in available sources, limiting associations to general techniques applicable to Windows Shell security bypass vulnerabilities. Specific TTPs may emerge with further analysis or exploit disclosures.

 

additional recommendations and information

1. Immediate Mitigation

  • Deploy the February 2026 Microsoft Patch Tuesday updates immediately to affected Windows systems, as Microsoft has released patches addressing this zero-day vulnerability in Windows Shell.
  • Restrict user interactions by disabling or limiting access to untrusted links and shortcut files through email filters, web proxies, and user training to prevent clicking malicious content.
  • Enable enhanced Windows SmartScreen protections and configure Group Policy to block execution of unverified files (e.g., via Computer Configuration > Administrative Templates > Windows Components > File Explorer > Hide entry points for Fast User Switching).

2. Patch and Monitor Systems

  • Vendor patch is available: Apply the Microsoft security updates from February 10, 2026, immediately, as confirmed in the MSRC advisory; test in a staging environment before full deployment due to its zero-day status and public disclosure.
  • Monitor for exploitation indicators: Use SIEM tools or Endpoint Detection and Response (EDR) to detect anomalous Shell activities, such as unexpected shortcut executions, bypassed SmartScreen prompts, or network-based file downloads leading to code execution.
  • Track MSRC (msrc.microsoft.com) for any follow-up advisories or out-of-band patches.

3. Network Security

  • Block malicious attack vectors: Implement web application firewalls(WAF) or proxies to filter traffic containing malicious links/shortcuts targeting Windows Shell; block domains/IPs associated with phishing campaigns exploiting this CVE via threat intelligence feeds.
  • Deploy IDS/IPS rules for signatures matching CVE-2026-21510exploitation attempts, focusing on network delivery of shortcut files (.lnk) or SmartScreen bypass patterns.
  • Isolate and segment vulnerable systems: Move internet-facing Windows endpoints behind firewalls, apply network segmentation, and monitor for lateral movement or unusual PowerShell/Shell invocations post-exploitation.

 

additional service offerings

Threat Detection & Response (TDR)
Avertium's TDR integrates all aspects of security operations into an XDR-informed threat detection and response system, providing proactive monitoring for security feature bypass vulnerabilities like CVE-2026-21510 in Windows Shell. It ensures continuous surveillance of network traffic and unauthorized access attempts, enabling rapid detection and mitigation of remote exploitation over the network.

Microsoft Security Solutions
Avertium's Microsoft Security Solutions optimize security in Microsoft environments, including assessments for safe deployment and custom threat detection rules tailored to Windows vulnerabilities. For CVE-2026-21510, these services analyze existing Windows configurations to identify bypass risks, maximize Defender investments for endpoint protection, and provide a three-week evaluation to enhance posture against protection mechanism failures.

Security Information and Event Management (SIEM)
Avertium's SIEM integration delivers holistic visibility across Windows and hybrid environments, detecting anomalous behavior indicative of security feature bypasses, such as unauthorized network-based access in Windows Shell. It optimizes SIEM platforms to correlate logs, prioritize alerts, and enable early response to prevent attacker success.

Attack Surface Management (ASM)
Avertium's ASM identifies and mitigates vulnerabilities in IT infrastructure, including Windows systems exposed to network attacks. For this CVE, ASM conducts testing and assessments to uncover blind spots in Windows Shell protections, prioritizing remediation to reduce the attack surface for unauthorized remote bypasses.

Governance, Risk, and Compliance (GRC)
Avertium's GRC services align security with regulations through compliance audits, risk management, and secure configuration enforcement. It addressesCVE-2026-21510 by evaluating access controls, implementing least-privilege policies in Windows environments, and developing roadmaps to prevent feature bypasses via structured governance.

 

 

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