CVE-2026-40538 in DiskStation Manager
Summary
by MITRE • 09/18/2026
An improper restriction of excessive authentication attempts vulnerability in Auto block in Synology DiskStation Manager (DSM) before 7.2.1-69057-10, 7.2.2-72806-7 and 7.3.2-86009-2 allows remote attackers to read limited files via brute-force attacks.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in Synology DiskStation Manager (DSM) versions prior to 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2 represents a critical failure in the implementation of account lockout mechanisms designed to mitigate brute-force attacks. This flaw is categorized under CWE-307, which describes Improper Restriction of Excessive Authentication Attempts. The core technical issue lies within the Auto block feature, a security control intended to temporarily or permanently disable user accounts after a specified number of failed login attempts. In the affected versions, this mechanism fails to properly enforce restrictions on authentication requests originating from remote sources, allowing attackers to bypass the intended rate-limiting and account lockout logic through sophisticated brute-force techniques.
From an operational perspective, this vulnerability enables unauthorized access by circumventing one of the primary defenses against credential stuffing and password guessing attacks. By exploiting the improper restriction, a remote attacker can systematically attempt multiple authentication combinations without triggering the defensive blocks that should have been activated after repeated failures. This capability significantly lowers the barrier for attackers to gain valid credentials, particularly in environments where weak or reused passwords are prevalent. The ability to read limited files indicates that successful exploitation leads not only to unauthorized access but also to data exfiltration, compromising the confidentiality of sensitive information stored on the NAS device.
The impact extends beyond simple account compromise. Since Synology DSM manages network-attached storage devices often used for critical business data and personal backups, a breach resulting from this vulnerability can lead to significant data loss or exposure. Attackers leveraging this flaw can access shared folders, user home directories, and potentially system configuration files depending on the privileges of the compromised account. This aligns with ATT&CK technique T1110.001, which covers Brute Force: Password Guessing, highlighting how attackers exploit weak authentication controls to infiltrate systems. The persistence of this vulnerability in multiple major DSM releases underscores a systemic issue in the validation logic governing security thresholds during high-volume login attempts.
Mitigation requires immediate action by system administrators and users operating affected versions. The primary remediation is to upgrade Synology DiskStation Manager to version 7.2.1-69057-10 or later, as well as updating any instances of DSM 7.2.2 beyond build 72806-7 and DSM 7.3.2 beyond build 86009-2 where the patch is available. Until patches are applied, organizations should implement compensating controls such as network-level access control lists to restrict administrative interface exposure to trusted IP addresses only. Additionally, enforcing strong password policies and enabling multi-factor authentication can reduce the risk of successful brute-force attacks even if the underlying software vulnerability remains unpatched in legacy systems. Regular monitoring of login logs for anomalous patterns of failed attempts is also recommended to detect potential exploitation activities early.