threat-modeling.md

Threat Model Analysis for nextcloud/server

Threat: Remote Code Execution (RCE) via Core Vulnerability

• Description: An attacker exploits a vulnerability in Nextcloud core PHP code to execute arbitrary code on the server. This is achieved by crafting malicious requests, exploiting file upload functionalities, or manipulating input parameters.

  • Impact: Full server compromise, complete control over Nextcloud instance and potentially the underlying server operating system, data breach (access, modification, deletion of all data), denial of service, malware deployment, reputational damage.

  • Affected Component: Nextcloud Core (various modules depending on the vulnerability).

  • Risk Severity: Critical

  • Mitigation Strategies:

    • Regularly update Nextcloud to the latest stable version.
    • Implement a Web Application Firewall (WAF).
    • Conduct regular code reviews and security audits.
    • Utilize static and dynamic code analysis tools.
    • Harden the server operating system and PHP environment.
    • Implement strong input validation and sanitization in the codebase.

Threat: Remote Code Execution (RCE) via Malicious App

• Description: An attacker installs or exploits a vulnerability in a third-party Nextcloud app to execute arbitrary code on the server. This can be through a vulnerable or intentionally malicious app, potentially escalating privileges from the app's context.

  • Impact: Server compromise, data breach, denial of service, malware deployment, potentially starting within the app's scope but likely to escalate.

  • Affected Component: Nextcloud Apps subsystem, specific vulnerable/malicious App.

  • Risk Severity: High (Potentially Critical)

  • Mitigation Strategies:

    • Carefully select and vet Nextcloud apps; use official App Store and verified apps.
    • Regularly review installed apps and their permissions.
    • Monitor app updates and security advisories, update promptly.
    • Consider app sandboxing/isolation (if available).
    • Report suspicious apps to Nextcloud security team.

Threat: Authentication Bypass

• Description: An attacker exploits a flaw in Nextcloud's authentication mechanisms to gain unauthorized access to user accounts, including administrator accounts. This could involve session manipulation, password reset flaws, or bypassing two-factor authentication.

  • Impact: Unauthorized access to user data, administrative functions, data manipulation, account takeover, potential for further attacks.

  • Affected Component: Authentication modules (login, session management, password reset, MFA).

  • Risk Severity: High

  • Mitigation Strategies:

    • Enforce strong password policies.
    • Implement and enforce Multi-Factor Authentication (MFA).
    • Regular security audits of authentication code.
    • Stay updated with security patches.
    • Securely configure session management.

Threat: Path Traversal/Local File Inclusion (LFI)

• Description: An attacker exploits a vulnerability to access files outside the intended webroot on the server. This allows reading sensitive configuration files, application code, or potentially system files, by manipulating file paths in requests.

  • Impact: Information disclosure (sensitive files, credentials, source code), potential for further exploitation, potentially leading to RCE in some scenarios.

  • Affected Component: File handling modules, file upload, components processing file paths.

  • Risk Severity: High (Due to potential for sensitive information disclosure and escalation)

  • Mitigation Strategies:

    • Strict input validation and sanitization for file paths.
    • Secure file handling practices in code.
    • Principle of least privilege for file system permissions.
    • Regular security scanning for path traversal.
    • Web Application Firewall (WAF).

Threat: Server-Side Request Forgery (SSRF)

• Description: An attacker exploits Nextcloud to make requests to internal or external resources on behalf of the server. This can be used to scan internal networks, access internal services, or exfiltrate data by manipulating URLs or parameters processed by Nextcloud.

  • Impact: Information disclosure about internal infrastructure, access to internal services, potential attacks on internal systems, data exfiltration.

  • Affected Component: Components making outbound HTTP requests (external storage, app store, webdav client, URL previews).

  • Risk Severity: High (Due to potential access to internal network and services)

  • Mitigation Strategies:

    • Input validation and sanitization for URLs.
    • Restrict outbound network access from the Nextcloud server (firewall).
    • Use allowlists for external requests.
    • Disable/restrict vulnerable features if not needed.
    • Implement proper error handling to prevent information leakage.

Threat: Insecure Deserialization

• Description: An attacker exploits insecure deserialization vulnerabilities in PHP code within Nextcloud. By manipulating serialized data, they can achieve arbitrary code execution when Nextcloud unserializes this data.

  • Impact: Remote Code Execution, full server compromise.

  • Affected Component: Components using PHP serialization (potentially core and apps).

  • Risk Severity: Critical

  • Mitigation Strategies:

    • Avoid unserialize() on untrusted data.
    • Use secure serialization methods like JSON.
    • Input validation and sanitization of serialized data.
    • Regular security audits and code reviews.
    • Stay updated with security patches.

Threat: Insecure Default Configuration

• Description: Insecure default settings in Nextcloud after installation (e.g., weak default admin credentials) can be exploited for initial access or easier exploitation of other vulnerabilities.

  • Impact: Initial access for attackers, easier exploitation, information disclosure, potential account takeover if default admin credentials are not changed.

  • Affected Component: Installation process, default configuration files, initial setup.

  • Risk Severity: High (If default admin credentials are not changed)

  • Mitigation Strategies:

    • Follow Nextcloud security hardening guidelines immediately after install.
    • Change default administrator credentials immediately.
    • Review and harden server configuration after installation.
    • Disable debug mode in production.
    • Regularly review and update server configuration.

Threat: Misconfigured File Permissions

• Description: Incorrect file permissions on the Nextcloud server file system can allow unauthorized access to sensitive files (config files, code, user data), leading to information disclosure or potential modification.

  • Impact: Information disclosure (configuration, credentials, source code, user data), potential privilege escalation, data breach.

  • Affected Component: Server file system, file permission settings, installation scripts, system administration.

  • Risk Severity: High (If sensitive files are exposed with read/write access)

  • Mitigation Strategies:

    • Properly set file permissions according to Nextcloud documentation.
    • Regularly audit file permissions.
    • Use tools to detect and remediate misconfigurations.
    • Implement file integrity monitoring.
    • Principle of least privilege for Nextcloud processes.

Threat: Vulnerabilities in PHP Dependencies

• Description: Vulnerabilities in third-party PHP libraries used by Nextcloud can be exploited through Nextcloud's usage of these libraries, potentially leading to various attacks.

  • Impact: Exploitation of dependency vulnerabilities, potentially leading to RCE, information disclosure, or other attacks.

  • Affected Component: Third-party PHP libraries and dependencies.

  • Risk Severity: High (Potentially Critical depending on the dependency vulnerability)

  • Mitigation Strategies:

    • Regularly update PHP dependencies.
    • Use dependency vulnerability scanning tools.
    • Monitor security advisories for PHP libraries.
    • Consider Software Composition Analysis (SCA) tools.