CVE-2026-21440 is a path traversal vulnerability classified under CWE-22 found in the AdonisJS web framework, specifically in the multipart file handling functionality of the @adonisjs/bodyparser package. AdonisJS is a popular TypeScript-first Node.js framework used to build web applications. The vulnerability allows a remote attacker to craft specially formed multipart requests that bypass pathname restrictions, enabling arbitrary file write operations to any location on the server filesystem. This can lead to overwriting critical system or application files, uploading malicious scripts, or planting backdoors, thereby compromising the server's confidentiality, integrity, and availability. The affected versions include all @adonisjs/bodyparser releases before 10.1.2 and prerelease versions from 11.0.0-next.0 up to but not including 11.0.0-next.6. The vulnerability requires no authentication or user interaction, making it highly exploitable remotely over the network. The CVSS 4.0 base score of 9.2 reflects the critical nature of this flaw, with network attack vector, low attack complexity, no privileges required, and no user interaction needed. Although no public exploits have been reported yet, the vulnerability's characteristics suggest a high likelihood of exploitation once weaponized. The issue was publicly disclosed on January 2, 2026, and patches are available in versions 10.1.2 and 11.0.0-next.6. Organizations using vulnerable versions should prioritize upgrading to these patched releases to prevent potential compromise.

For European organizations, this vulnerability poses a significant risk, particularly for those relying on AdonisJS for web application development and deployment. Successful exploitation can lead to arbitrary file writes, enabling attackers to deploy web shells, modify application logic, or disrupt services, resulting in data breaches, service outages, and reputational damage. Sectors such as finance, healthcare, government, and critical infrastructure that host sensitive data or provide essential services are especially vulnerable. The ability to write files anywhere on the server can facilitate lateral movement and persistent access within networks. Given the widespread adoption of Node.js frameworks in Europe’s technology ecosystem, the potential attack surface is considerable. Moreover, regulatory frameworks like GDPR impose strict data protection requirements, and exploitation could lead to severe compliance violations and financial penalties. The lack of authentication or user interaction required for exploitation increases the urgency for European organizations to address this vulnerability promptly.

1. Immediate upgrade of @adonisjs/bodyparser to version 10.1.2 or later, or 11.0.0-next.6 or later, to apply the official patch. 2. Implement strict input validation and sanitization on file upload endpoints to detect and block suspicious pathname characters or sequences (e.g., ../). 3. Employ runtime application self-protection (RASP) tools that monitor and block unauthorized filesystem access attempts. 4. Restrict file system permissions for the application process to the minimum necessary, preventing writes outside designated directories. 5. Conduct thorough code reviews and penetration testing focusing on file upload and multipart handling components. 6. Monitor logs for unusual file write activities or access patterns indicative of exploitation attempts. 7. Use web application firewalls (WAFs) with custom rules to detect and block path traversal payloads targeting multipart requests. 8. Educate development teams on secure file handling best practices and the risks of path traversal vulnerabilities. 9. Maintain an inventory of applications using AdonisJS to ensure all instances are identified and patched. 10. Prepare incident response plans to quickly address potential exploitation scenarios.