CVE-2019-15613 in Nextcloud Server
Summary
by MITRE
A bug in Nextcloud Server 17.0.1 causes the workflow rules to depend their behaviour on the file extension when checking file mimetypes.
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Analysis
by VulDB Data Team • 03/28/2024
The vulnerability identified as CVE-2019-15613 affects Nextcloud Server version 17.0.1 and represents a significant security flaw in the platform's workflow rule implementation. This issue stems from an improper handling of file mime types within the server's automated workflow processing system, creating a potential vector for bypassing security controls and access restrictions. The vulnerability specifically manifests when the system's workflow rules evaluate file characteristics based on file extensions rather than properly validating the actual file content, leading to inconsistent and potentially dangerous behavior in automated security processes.
The technical flaw resides in the workflow engine's reliance on file extension parsing for determining mime type validation during automated file processing. When Nextcloud processes files through configured workflow rules, the system incorrectly uses file extensions as the primary determinant for mime type classification rather than performing proper content-based validation. This approach creates a scenario where malicious actors can manipulate workflow behavior by simply changing file extensions while maintaining the actual file content, effectively bypassing security mechanisms that should be triggered based on file type. The vulnerability operates at the application layer and directly impacts Nextcloud's automated file handling capabilities, particularly affecting workflows that depend on mime type detection for security enforcement.
The operational impact of this vulnerability extends beyond simple bypass scenarios and creates a substantial risk to organizational security posture. Attackers could exploit this weakness to circumvent automated security measures such as virus scanning, content filtering, or access control policies that are configured to trigger based on specific file types. For example, a malicious user could rename a malicious executable file with a legitimate extension like .pdf or .docx, causing the workflow rules to treat it as a safe file type and potentially bypass security scanning processes. This vulnerability particularly affects environments where Nextcloud is used for document management, file sharing, or collaborative workspaces where automated security controls are critical for protecting sensitive data. The flaw undermines the integrity of automated security enforcement mechanisms and could lead to unauthorized access, data exfiltration, or execution of malicious code within the Nextcloud environment.
Organizations should implement immediate mitigations including updating to Nextcloud Server versions that address this vulnerability, typically versions 17.0.2 or later where proper mime type validation has been implemented. Security teams should also review and validate existing workflow rules to ensure they are not overly dependent on file extension matching and instead rely on proper content-based validation methods. Additionally, implementing network-based security controls such as deep packet inspection and content filtering can provide additional layers of protection against exploitation attempts. This vulnerability aligns with CWE-20 Improper Input Validation and follows patterns commonly associated with attack techniques in the ATT&CK framework under T1059 Command and Scripting Interpreter and T1204 User Execution. Organizations should also consider implementing principle of least privilege access controls and regular security audits of workflow configurations to prevent exploitation of similar weaknesses in automated systems.