CVE-2026-9548 in Chat Server
Summary
by MITRE • 08/28/2026
An improper neutralization of input during web page generation ('Cross-site Scripting') vulnerability in extract domain in Synology Chat Server before 2.4.5-22148 allows remote authenticated users, via a UI interaction, to read or write restricted files and conduct limited denial-of-service attacks in DSM.
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Analysis
by VulDB Data Team • 08/28/2026
The identified vulnerability represents a critical security flaw within the Synology Chat Server application, specifically affecting versions prior to 2.4.5-22148. This issue is classified as an improper neutralization of input during web page generation, commonly known as Cross-Site Scripting or XSS. The core technical failure lies in the extract domain functionality, where user-supplied data is not adequately sanitized before being processed and rendered by the application's interface. While traditional XSS vulnerabilities are often associated with stealing session cookies or defacing websites, this specific implementation flaw has been escalated due to its integration with the underlying DiskStation Manager (DSM) operating system environment. The vulnerability allows for a more severe impact than standard script injection because it bridges the gap between the web application layer and the host operating system's file integrity mechanisms.
Remote authenticated users can exploit this weakness by interacting with the user interface in a manner that triggers the improper input handling within the extract domain feature. By crafting specific inputs, an attacker can inject malicious scripts or commands that are executed in the context of the victim’s session or the server process itself. Because Synology Chat Server operates with elevated privileges relative to standard web applications, the execution environment provides access to system resources that would otherwise be restricted. This architectural positioning is what transforms a typical client-side scripting issue into a potential remote code execution vector affecting the host operating system. The attacker does not need physical access or local shell access; they only require valid authentication credentials for the Synology Chat Server service, which are often shared across the NAS ecosystem if single sign-on features are enabled or passwords are reused.
The operational impact of this vulnerability is severe and multifaceted. Primarily, it allows attackers to read restricted files on the DSM system. This capability compromises data confidentiality by exposing sensitive configuration files, user credentials stored in plaintext or weakly hashed formats, private keys, and proprietary business data residing within shared folders that may have been inadvertently exposed through misconfigured permissions exacerbated by the exploit. Furthermore, the vulnerability enables unauthorized write operations to these restricted files. An attacker could modify system configurations, inject malicious scripts into startup processes, or alter critical application binaries, thereby establishing persistence on the device. This level of control effectively grants the attacker administrative-level access to the NAS appliance without needing valid root credentials directly.
In addition to data theft and modification, this vulnerability facilitates limited denial-of-service attacks against DSM. By manipulating system resources through the injected code, an attacker can cause processes to hang, consume excessive CPU or memory resources, or trigger crashes in critical services that manage storage pools or network interfaces. This disruption impacts not only the Synology Chat Server itself but also other applications and users relying on the NAS infrastructure for data access and collaboration. The availability of these denial-of-service capabilities means that even if an attacker does not seek to exfiltrate data, they can render the entire system unusable for legitimate business operations, causing significant downtime and operational loss.
From a classification perspective, this vulnerability aligns with CWE-79, which covers Improper Neutralization of Input During Web Page Generation (Cross-site Scripting). However, due to its ability to interact with file systems and cause service disruption, it also touches upon CWE-264: Permissions, Privileges, and Access Controls, as the exploit leverages existing privileges to access restricted resources. In terms of tactical mapping within the MITRE ATT&CK framework for Enterprise, this behavior corresponds to T1059 Command and Scripting Interpreter, specifically through web-based protocols like JavaScript or HTML injection. It also relates to T1222 File and Directory Permissions Modification if write operations are successfully executed, and potentially T1496 Resource Hijacking when denial-of-service effects are observed.
Mitigation for this vulnerability requires immediate action by system administrators. The primary remediation step is to upgrade the Synology Chat Server package to version 2.4.5-22148 or later, where the input validation logic in the extract domain has been corrected to properly sanitize user inputs before processing. Until an update can be applied, organizations should restrict network access to the Synology DSM and its associated services using firewall rules, ensuring that only trusted IP addresses can reach these interfaces. Additionally, enforcing strict password policies and multi-factor authentication for all administrative accounts reduces the likelihood of credential compromise leading to exploitation. Regular auditing of file permissions within shared folders is also recommended to minimize the blast radius in case a similar vulnerability exists elsewhere in the system architecture.