CVE-2018-13299 in Calendar
Summary
by MITRE
Relative path traversal vulnerability in Attachment Uploader in Synology Calendar before 2.2.2-0532 allows remote authenticated users to upload arbitrary files via the filename parameter.
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Analysis
by VulDB Data Team • 08/21/2023
The vulnerability identified as CVE-2018-13299 represents a critical relative path traversal flaw within the Attachment Uploader component of Synology Calendar software. This issue affects versions prior to 2.2.2-0532 and creates a significant security risk by allowing authenticated remote attackers to bypass intended file upload restrictions. The vulnerability specifically resides in how the application processes the filename parameter during attachment uploads, enabling attackers to manipulate file paths and potentially execute arbitrary code on the affected system. The flaw stems from inadequate input validation and sanitization mechanisms that fail to properly restrict file path components, allowing malicious users to traverse directory structures beyond intended boundaries.
The technical implementation of this vulnerability leverages the inherent trust placed in authenticated user sessions within the Synology Calendar application. When users attempt to upload attachments through the calendar interface, the system processes the filename parameter without sufficient validation to prevent directory traversal sequences such as ../ or ..\ that would normally be blocked by proper security controls. This weakness creates an attack surface where authenticated users can manipulate the upload process to place malicious files in unintended directories, potentially including system directories or web root folders. The vulnerability operates at the application layer and specifically targets the file handling mechanisms that govern attachment storage within the calendar system, making it particularly dangerous for environments where calendar applications handle sensitive data or serve as part of broader enterprise infrastructure.
The operational impact of CVE-2018-13299 extends beyond simple unauthorized file placement, as it can potentially enable more severe attacks including remote code execution, privilege escalation, and persistent backdoor installation. An attacker who successfully exploits this vulnerability can upload malicious files such as web shells, scripts, or binary executables that may be executed by the web server or application process. The attack requires only authentication to the calendar application, which is often readily available in enterprise environments where calendar services are used by multiple users. This vulnerability particularly affects organizations using Synology NAS devices with integrated calendar services, creating potential exposure points in network infrastructure where attackers could gain persistent access to systems. The impact is amplified when calendar applications are configured to store uploaded files in web-accessible directories, as this enables direct execution of uploaded malicious content through web browsers.
Organizations should implement immediate mitigations including updating to Synology Calendar version 2.2.2-0532 or later, which contains patches addressing the path traversal vulnerability. Network segmentation and access controls should be reviewed to limit exposure of calendar services to untrusted networks, while monitoring should be enhanced to detect unusual file upload patterns. Security teams should also implement input validation controls at multiple layers including web application firewalls, file type restrictions, and directory access controls to prevent similar vulnerabilities from being exploited in other components. The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, and represents a common attack pattern categorized under ATT&CK technique T1078 for Valid Accounts and T1059 for Command and Scripting Interpreter, highlighting the need for comprehensive security controls. Regular security assessments and vulnerability scanning should be conducted to identify and remediate similar path traversal issues in other applications and systems within the organization's infrastructure.