CVE-2023-26482 in Server
Summary
by MITRE • 03/30/2023
Nextcloud server is an open source home cloud implementation. In affected versions a missing scope validation allowed users to create workflows which are designed to be only available for administrators. Some workflows are designed to be RCE by invoking defined scripts, in order to generate PDFs, invoking webhooks or running scripts on the server. Due to this combination depending on the available apps the issue can result in a RCE at the end. It is recommended that the Nextcloud Server is upgraded to 24.0.10 or 25.0.4. Users unable to upgrade should disable app `workflow_scripts` and `workflow_pdf_converter` as a mitigation.
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Analysis
by VulDB Data Team • 04/21/2023
The vulnerability identified as CVE-2023-26482 represents a critical authorization bypass flaw within the Nextcloud server platform that undermines the security model of the application. This issue stems from insufficient scope validation mechanisms that permit regular users to manipulate workflow configurations that should be restricted to administrative privileges only. The vulnerability affects Nextcloud server versions prior to 24.0.10 and 25.0.4, creating a pathway for privilege escalation that could ultimately lead to complete system compromise. The flaw specifically impacts the workflow management system where certain workflows are designed to execute server-side operations including script execution, webhook invocation, and PDF generation capabilities. These workflows when properly restricted would only be accessible to administrators, but due to the missing validation checks, regular authenticated users can manipulate them to gain unauthorized access to system resources.
The technical implementation of this vulnerability involves the improper validation of user permissions within the workflow engine of Nextcloud. When users create or modify workflows, the system should verify that the requesting user possesses the appropriate administrative privileges before allowing configuration changes that could result in system-level operations. However, this validation process fails to properly enforce scope restrictions, allowing authenticated users to bypass normal access controls. The vulnerability manifests through the workflow scripts and workflow pdf converter applications which are designed to execute arbitrary commands on the server. These applications, when combined with the missing scope validation, create a dangerous combination where users can potentially execute arbitrary code on the target system. The underlying cause can be categorized under CWE-285: Improper Authorization, which specifically addresses situations where the system fails to properly enforce access controls for protected resources.
The operational impact of CVE-2023-26482 extends beyond simple privilege escalation to encompass full system compromise capabilities. When combined with available Nextcloud applications that support script execution and webhook functionality, an attacker can potentially execute arbitrary commands on the target server with the privileges of the web application user. This scenario creates multiple attack vectors including remote code execution, data exfiltration, and persistence mechanisms. The vulnerability's severity is amplified by the fact that it affects core workflow functionality that many organizations rely upon for automation processes, making it particularly dangerous in environments where Nextcloud serves as a central collaboration platform. Attackers could leverage this vulnerability to establish persistent backdoors, escalate privileges further within the network, or use the compromised system as a launch point for additional attacks. The impact aligns with ATT&CK technique T1078.004: Valid Accounts, Valid Accounts: Cloud Accounts, where attackers can leverage authenticated access to escalate privileges and maintain persistence within cloud environments.
Organizations affected by this vulnerability should prioritize immediate remediation through upgrading to Nextcloud versions 24.0.10 or 25.0.4, which contain the necessary fixes for the scope validation issue. The upgrade process should be carefully planned to minimize disruption to business operations while ensuring complete protection against the vulnerability. For organizations unable to perform immediate upgrades, the recommended mitigation strategy involves disabling the vulnerable applications workflow_scripts and workflow_pdf_converter. This approach effectively neutralizes the attack vector by removing the capability to execute arbitrary commands through the workflow engine. Security teams should also implement monitoring for unusual workflow activity or unauthorized configuration changes that might indicate exploitation attempts. Additionally, organizations should review their Nextcloud configuration to ensure that administrative privileges are properly restricted and that least privilege principles are enforced throughout the system. The mitigation strategy aligns with ATT&CK technique T1566.002: Phishing: Spearphishing Attachment, where organizations should implement application control measures to prevent unauthorized execution of potentially malicious scripts within their environment. Regular security assessments and vulnerability scanning should be conducted to identify similar scope validation issues in other applications and ensure comprehensive protection against privilege escalation attacks.