CVE-2020-5284 in Next.js
Summary
by MITRE
Next.js versions before 9.3.2 have a directory traversal vulnerability. Attackers could craft special requests to access files in the dist directory (.next). This does not affect files outside of the dist directory (.next). In general, the dist directory only holds build assets unless your application intentionally stores other assets under this directory. This issue is fixed in version 9.3.2.
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Analysis
by VulDB Data Team • 05/10/2025
The vulnerability described in CVE-2020-5284 represents a critical directory traversal flaw within the Next.js web application framework that affects versions prior to 9.3.2. This security weakness enables malicious actors to exploit improperly validated file paths through specially crafted HTTP requests, potentially allowing unauthorized access to sensitive build artifacts stored within the application's dist directory, commonly referred to as the .next directory. The vulnerability specifically targets the server-side rendering and static site generation capabilities of Next.js, where the framework processes incoming requests and maps them to appropriate response handlers. Attackers can leverage this flaw to bypass normal file system access controls and retrieve files that should remain restricted within the application's build environment. The security implications extend beyond simple information disclosure, as the dist directory may contain compiled JavaScript bundles, CSS files, and other build-time assets that could reveal implementation details or potentially expose sensitive configuration information. This vulnerability aligns with CWE-22, which categorizes directory traversal attacks as a fundamental weakness in input validation and file system access controls. The issue manifests because Next.js fails to properly sanitize user-supplied path parameters during request processing, allowing attackers to manipulate the path resolution logic through crafted URL sequences that traverse parent directories using techniques such as double dots or encoded path separators.
The operational impact of this vulnerability is significant for organizations running affected Next.js applications, as it creates a potential attack vector for data exfiltration and reconnaissance activities. While the vulnerability is limited to accessing files within the .next directory and does not permit access to arbitrary files outside this specific location, the build artifacts stored there often contain sensitive information including compiled code, embedded configuration data, and potentially even secrets that were inadvertently included during the build process. The attack surface becomes particularly concerning when applications store additional assets or configuration files within the dist directory, as these could contain credentials, API keys, or other sensitive materials that should remain protected from unauthorized access. Security teams must consider that this vulnerability could enable attackers to gain insights into application architecture, build processes, and potentially identify other related vulnerabilities within the system. The exploitation of this flaw typically requires minimal privileges and can be automated through common web exploitation tools, making it particularly dangerous for organizations that do not maintain proper network segmentation or monitoring controls around their web application infrastructure. This vulnerability demonstrates the importance of proper input validation and the principle of least privilege in web application security, where all user-provided input should be treated as potentially malicious and subjected to rigorous sanitization before being processed by the application.
Mitigation strategies for CVE-2020-5284 primarily focus on immediate version upgrades to Next.js 9.3.2 or later, which includes the necessary patches to prevent directory traversal attacks against the .next directory. Organizations should implement comprehensive patch management procedures to ensure all affected applications are updated promptly, particularly in production environments where the vulnerability could be exploited by threat actors. Network-based mitigations such as web application firewalls can provide additional protection layers, though these should not be relied upon as the sole defense mechanism. Security monitoring should be enhanced to detect unusual access patterns to application directories, particularly around build artifacts and configuration files. Regular security audits should verify that no sensitive information is stored within the .next directory or other build directories, and that proper file system permissions are enforced to limit access to only necessary system accounts. The vulnerability also underscores the importance of following secure coding practices and conducting regular security assessments of web frameworks and libraries to identify potential weaknesses before they can be exploited by adversaries. Organizations should implement automated security scanning tools that can detect vulnerable versions of dependencies and alert security teams to remediation requirements. This incident highlights the need for continuous security monitoring and the importance of maintaining up-to-date security patches across all application components, as vulnerabilities in widely-used frameworks like Next.js can have widespread implications for the entire ecosystem of applications built using these technologies. The ATT&CK framework categorizes this type of vulnerability under T1083 - File and Directory Discovery, where attackers can enumerate and access files that should remain protected.