CVE-2019-12739 in Extract Add-On
Summary
by MITRE
lib/Controller/ExtractionController.php in the Extract add-on before 1.2.0 for Nextcloud allows Remote Code Execution via shell metacharacters in a RAR filename via ajax/extractRar.php (nameOfFile and directory parameters).
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Analysis
by VulDB Data Team • 09/28/2023
The vulnerability identified as CVE-2019-12739 represents a critical remote code execution flaw within the Nextcloud Extract add-on, specifically affecting versions prior to 1.2.0. This security issue resides in the lib/Controller/ExtractionController.php file and exploits a dangerous input handling mechanism that allows attackers to inject shell metacharacters into RAR filenames. The vulnerability manifests through the ajax/extractRar.php endpoint where the nameOfFile and directory parameters are processed without adequate sanitization, creating a pathway for arbitrary command execution on the affected system. The flaw directly enables attackers to execute malicious commands on the server by manipulating RAR archive filenames, potentially compromising the entire Nextcloud instance and underlying infrastructure.
The technical nature of this vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and CWE-94, which covers improper control of generation of code. The vulnerability operates by bypassing normal input validation mechanisms that should prevent shell metacharacters from being processed as part of file names. When a RAR file is uploaded with maliciously crafted filename containing shell operators such as semicolons, ampersands, or command substitution characters, the system processes these inputs directly without proper sanitization, allowing attackers to inject and execute arbitrary shell commands with the privileges of the Nextcloud service account. This type of vulnerability falls under the ATT&CK technique T1059.001 for command and scripting interpreter, specifically targeting the execution of malicious commands through the system's shell interface.
The operational impact of this vulnerability is severe and far-reaching, as it provides attackers with complete control over the affected Nextcloud server. Successful exploitation enables threat actors to execute arbitrary code, potentially leading to data exfiltration, system compromise, privilege escalation, and further lateral movement within the network. The vulnerability affects organizations using Nextcloud with the Extract add-on, making it particularly dangerous for businesses that rely on cloud storage solutions for sensitive data. Attackers can leverage this vulnerability to install backdoors, modify system configurations, access user data, or use the compromised server as a launching point for attacks against other systems in the network. The remote nature of the vulnerability means that attackers can exploit it from anywhere on the internet without requiring physical access to the system.
Mitigation strategies for CVE-2019-12739 focus on immediate patching and input validation improvements. Organizations should immediately upgrade to Nextcloud Extract add-on version 1.2.0 or later, which contains the necessary security fixes. System administrators should implement comprehensive input validation for all file name parameters, particularly those related to archive extraction operations, ensuring that shell metacharacters are properly escaped or removed before processing. Network segmentation and access controls should be implemented to limit exposure of the affected service to trusted networks only. Regular security audits and vulnerability assessments should be conducted to identify similar input handling issues in other components. Additionally, implementing web application firewalls and monitoring for suspicious command execution patterns can help detect and prevent exploitation attempts. The vulnerability demonstrates the critical importance of proper input sanitization in web applications and highlights the need for defense-in-depth strategies that protect against both known and unknown vulnerabilities in enterprise storage solutions.