CVE-2022-41882 in Desktop Client
Summary
by MITRE • 11/11/2022
The Nextcloud Desktop Client is a tool to synchronize files from Nextcloud Server with your computer. In version 3.6.0, if a user received a malicious file share and has it synced locally or the virtual filesystem enabled and clicked a nc://open/ link it will open the default editor for the file type of the shared file, which on Windows can also sometimes mean that a file depending on the type, e.g. "vbs", is being executed. It is recommended that the Nextcloud Desktop client is upgraded to version 3.6.1. As a workaround, users can block the Nextcloud Desktop client 3.6.0 by setting the `minimum.supported.desktop.version` system config to `3.6.1` on the server, so new files designed to use this attack vector are not downloaded anymore. Already existing files can still be used. Another workaround would be to enforce shares to be accepted by setting the `sharing.force_share_accept` system config to `true` on the server, so new files designed to use this attack vector are not downloaded anymore. Already existing shares can still be abused.
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Analysis
by VulDB Data Team • 12/17/2022
The vulnerability identified as CVE-2022-41882 affects the Nextcloud Desktop Client version 3.6.0, representing a significant security risk that exploits user interaction with malicious file shares within the synchronization environment. This flaw resides in the client's handling of nc://open/ protocol links that are generated when users receive shared files through the Nextcloud Server infrastructure. The vulnerability creates an execution path where clicking on these specially crafted links can trigger automatic opening of files with the system's default editor, potentially leading to arbitrary code execution on Windows systems where file types like .vbs (Visual Basic Script) can be executed directly.
The technical implementation of this vulnerability demonstrates a classic privilege escalation attack vector through social engineering and protocol manipulation. When a user clicks an nc://open/ link, the desktop client bypasses normal security boundaries by directly invoking the system's default application handler for the file type. This behavior creates an attack surface where malicious actors can craft shares containing executable scripts or documents that automatically execute upon user interaction. The vulnerability specifically impacts Windows environments where the default file association system can be leveraged to execute malicious code, making it particularly dangerous in enterprise environments where users may encounter such shares through legitimate collaboration workflows.
From an operational security perspective, this vulnerability represents a critical risk to organizations relying on Nextcloud for file synchronization, as it allows attackers to potentially execute malicious code on target systems without requiring additional exploitation steps beyond user interaction. The attack requires minimal user engagement, making it particularly effective in phishing scenarios or when users are unaware of the security implications of accepting shared files. The vulnerability's impact extends beyond simple file access, as it can potentially lead to full system compromise depending on the user's privileges and the nature of the malicious files contained within the shares.
The recommended remediation approach involves upgrading to Nextcloud Desktop Client version 3.6.1, which addresses the core protocol handling issue by implementing proper validation and sandboxing of file opening operations. Additional server-side mitigations include setting the `minimum.supported.desktop.version` configuration parameter to 3.6.1, which prevents older vulnerable clients from downloading files that could exploit this vector. This server-side enforcement ensures that even if users have older clients installed, they cannot download potentially malicious shares that rely on this vulnerability. Alternative server-side controls include enabling the `sharing.force_share_accept` configuration option, which requires explicit user acceptance of shares before they are downloaded, adding an additional layer of security through user verification before file synchronization occurs.
This vulnerability aligns with CWE-78 and CWE-74 categories related to command injection and code injection flaws, while also demonstrating characteristics of ATT&CK technique T1059.007 for Windows Scripting and T1203 for Exploitation for Client Execution. The attack vector specifically leverages user interaction with file shares and protocol handlers, making it particularly relevant to the ATT&CK framework's focus on initial access and execution phases. Organizations should consider implementing network-level controls to monitor for nc:// protocol usage and establish clear policies regarding file share acceptance, particularly for sensitive environments where automated execution of scripts or documents could pose significant risks to overall security posture.