CVE-2026-70264 in Defender
Summary
by MITRE • 10/13/2026
Improper link resolution before file access ('link following') in Microsoft Defender allows an authorized attacker to disclose information locally.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified as improper link resolution prior to file access, commonly referred to as a symlink or symbolic link following attack within the context of Microsoft Defender, represents a significant class of security flaws where software fails to properly validate the target of a symbolic link before performing operations on it. This specific flaw allows an attacker who has local execution privileges and sufficient permissions to manipulate filesystem objects to redirect file access requests from intended secure locations to arbitrary files or directories on the system. By creating malicious symbolic links that point to sensitive configuration files, credential stores, or other protected resources, a privileged process running under Microsoft Defender can be tricked into reading data it was not originally authorized to access. This mechanism bypasses standard discretionary access control lists because the operating system resolves the link before checking permissions on the final target, effectively allowing the elevated service to read any file accessible by its account context.
From a technical perspective, this vulnerability exploits the atomicity gap or lack of validation between the creation and usage of symbolic links in Windows NTFS filesystems. When an application prepares to open a file for reading, it should verify that the path does not traverse through unintended junction points or symlinks that could lead outside the expected directory tree. In this case, Microsoft Defender's internal logic likely constructs paths dynamically based on user input or temporary files without adequately checking if those paths resolve to unexpected locations via symbolic links. An attacker can exploit this by pre-creating a symlink in a location where they have write access but which points to a sensitive file located elsewhere with restricted read permissions for the attacker’s own account, yet accessible to the Defender service account. When Defender subsequently attempts to process or scan that path, it follows the link and reads the protected content, leading to an unauthorized disclosure of information.
The operational impact of this vulnerability is primarily focused on local privilege escalation through information disclosure rather than direct code execution. While the attacker does not gain immediate administrative control over the system by exploiting this flaw alone, they can extract sensitive data such as cached credentials, encryption keys, or internal configuration details that may facilitate further attacks. For instance, disclosed tokens or hashes could be used in pass-the-hash attacks to move laterally across a network if those credentials have broader privileges elsewhere. Additionally, knowledge of internal system architecture and file structures gained through this disclosure can aid an attacker in crafting more sophisticated exploits against other components within the Microsoft Defender suite or related enterprise security infrastructure. This aligns with the ATT&CK technique T1083, which covers File and Directory Discovery, as well as T1552.004 for Unsecured Credentials if sensitive data is retrieved.
Mitigation strategies for this vulnerability involve both immediate patching by Microsoft to address the code-level flaw in link validation logic and proactive administrative hardening of affected systems until patches are applied. Administrators should ensure that symbolic links are restricted where possible, particularly in directories accessible to standard users but processed by elevated services. Implementing strict file system access controls and auditing policies can help detect unusual symlink creation activities. Furthermore, applying the latest security updates provided by Microsoft is critical as these typically include fixes for improper link resolution issues within Defender components. Organizations should also monitor for anomalous file access patterns that might indicate exploitation attempts, leveraging endpoint detection and response tools to identify processes accessing unexpected paths via symbolic links.