CVE-2021-32734 in Server
Summary
by MITRE • 07/13/2021
Nextcloud Server is a Nextcloud package that handles data storage. In versions prior to 19.0.13, 20.011, and 21.0.3, the Nextcloud Text application shipped with Nextcloud Server returned verbatim exception messages to the user. This could result in a full path disclosure on shared files. The issue was fixed in versions 19.0.13, 20.0.11, and 21.0.3. As a workaround, one may disable the Nextcloud Text application in Nextcloud Server app settings.
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Analysis
by VulDB Data Team • 07/15/2021
The vulnerability identified as CVE-2021-32734 affects the Nextcloud Server platform, specifically impacting versions prior to 19.0.13, 20.0.11, and 21.0.3. This security flaw resides within the Nextcloud Text application component that is bundled with the Nextcloud Server package for handling data storage operations. The vulnerability represents a critical information disclosure issue that occurs when the application processes exception handling errors during file operations. When users encounter errors while accessing shared files through the Nextcloud Text application, the system inadvertently returns complete exception messages containing sensitive path information to end users. This behavior creates a significant security risk as it exposes the underlying file system structure and server paths to unauthorized individuals who might exploit this information for further attacks.
The technical implementation flaw stems from inadequate error handling mechanisms within the Nextcloud Text application's exception processing code. When file operations fail, particularly during shared file access scenarios, the application fails to sanitize exception messages before presenting them to users. This insecure coding practice directly violates security principles outlined in CWE-209, which addresses information exposure through exception messages, and aligns with ATT&CK technique T1082 for system information discovery. The vulnerability manifests when users attempt to access shared files through the text application, triggering error conditions that result in full path disclosure. The exposed paths can include server directory structures, file locations, and potentially sensitive system information that could aid attackers in mapping the target environment and identifying potential attack vectors.
The operational impact of this vulnerability extends beyond simple information disclosure, creating substantial risks for organizations using affected Nextcloud Server versions. Attackers who can access shared files through the Nextcloud Text application can leverage the disclosed path information to perform reconnaissance activities, map the server infrastructure, and potentially identify additional vulnerabilities within the system. The exposed full paths may reveal critical information about the server configuration, file system layout, and potentially sensitive directory structures that could be exploited in subsequent attacks. Organizations using affected versions face increased risk of privilege escalation, lateral movement, and other advanced persistent threats that could compromise the integrity and confidentiality of their data storage systems. The vulnerability particularly affects environments where shared files are frequently accessed through the text application, making it a significant concern for enterprises relying on Nextcloud for collaborative document management.
The remediation for CVE-2021-32734 involves upgrading to the patched versions 19.0.13, 20.0.11, or 21.0.3, which implement proper exception handling and error message sanitization. Organizations should immediately deploy these updates to protect their Nextcloud Server installations from exploitation. As a temporary workaround, administrators can disable the Nextcloud Text application through the application settings, effectively preventing users from triggering the vulnerable code path. This mitigation strategy aligns with defensive cybersecurity practices and provides immediate protection while longer-term upgrades are implemented. Security teams should also conduct comprehensive vulnerability assessments to ensure that no other applications or components within their Nextcloud deployments might be susceptible to similar information disclosure vulnerabilities. The fix addresses the root cause by implementing proper input validation and output sanitization for exception messages, ensuring that users only receive generic error information while system administrators maintain access to detailed diagnostic information for legitimate troubleshooting purposes.