CVE-2026-40530 in DiskStation Manager
Summary
by MITRE • 09/18/2026
An improper neutralization of CRLF sequences ('CRLF injection') vulnerability in User API in Synology DiskStation Manager (DSM) before 7.2.1-69057-10, 7.2.2-72806-7 and 7.3.2-86009-2 allows remote authenticated users to read or write arbitrary files and conduct denial-of-service attacks after the system is rebooted.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified as an improper neutralization of Carriage Return Line Feed sequences, commonly referred to as CRLF injection, resides within the User API component of Synology DiskStation Manager versions prior to 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2. This flaw allows remote authenticated users to manipulate HTTP headers or input fields by injecting newline characters into data streams that are subsequently processed without adequate sanitization. In web application architecture, CRLF sequences serve as delimiters for header lines in the Hypertext Transfer Protocol. When an application fails to properly validate and escape these special characters within user-supplied input, it creates a pathway for attackers to inject arbitrary HTTP headers or even split requests into multiple distinct messages. This specific implementation flaw is categorized under CWE-138, which covers protocol injection vulnerabilities where improper neutralization of sequence elements leads to unintended execution of commands or data manipulation.
The operational impact of this vulnerability extends beyond simple header manipulation due to the context in which it occurs within the DiskStation Manager environment. Because the affected component handles user authentication and session management logic, successful exploitation can lead to severe consequences including unauthorized file access and system disruption. An attacker with valid credentials can leverage the CRLF injection to modify response headers or inject malicious cookies that alter the behavior of subsequent requests. This capability enables the reading of arbitrary files on the server by manipulating cache control directives or redirecting responses to exfiltrate sensitive configuration data, database contents, or user credentials stored in plaintext within system logs or temporary files. Furthermore, the ability to write arbitrary files allows an attacker to persist malicious scripts or backdoors that survive system reboots, effectively establishing a persistent foothold on the compromised NAS device.
Beyond confidentiality and integrity breaches, this vulnerability facilitates denial-of-service attacks against the target infrastructure. By injecting malformed sequences into HTTP responses, an attacker can cause the web server or associated services to crash, enter infinite loops, or consume excessive resources while attempting to parse invalid header structures. This disruption renders the storage system unavailable for legitimate users, impacting business continuity and data accessibility. The persistence of these effects after a reboot indicates that the vulnerability is not merely transient but affects core configuration files or startup scripts that are loaded during initialization phases. This characteristic aligns with ATT&CK technique T1505.003, Server Software Component: Web Shell, as well as T1496, Resource Hijacking, depending on whether the primary goal is data exfiltration or service disruption.
Mitigation strategies must prioritize immediate patching to address the root cause of the input validation failure. Administrators should upgrade Synology DiskStation Manager to version 7.2.1-69057-10 or later for the 7.2 branch, version 7.2.2-72806-7 or later for the 7.2.2 branch, and version 7.3.2-86009-2 or later for the 7.3 branch. These updates contain specific fixes that enforce strict validation of user input within the User API endpoints, ensuring that CRLF characters are either rejected or safely encoded before processing. In environments where immediate patching is not feasible due to operational constraints, network-level controls such as Web Application Firewalls can be configured to detect and block HTTP requests containing anomalous newline sequences in headers or parameters. Additionally, implementing strict access control policies for the User API endpoints limits exposure by ensuring that only necessary administrative accounts have privileges to interact with these interfaces, thereby reducing the attack surface available to potential adversaries seeking to exploit this flaw.