CVE-2026-21440 is a path traversal vulnerability classified under CWE-22, found in the multipart file handling mechanism of the AdonisJS web framework, specifically in the @adonisjs/bodyparser package. AdonisJS is a popular TypeScript-first Node.js framework used for building web applications. The vulnerability allows a remote attacker to craft multipart file upload requests that bypass directory restrictions, enabling arbitrary file writes to any location on the server filesystem. This can lead to overwriting critical system files, uploading web shells, or injecting malicious code, potentially resulting in full server compromise. The flaw affects all @adonisjs/bodyparser versions before 10.1.2 and prerelease 11.x versions prior to 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 vector (AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N) indicates network attack vector, low complexity, partial attack complexity, no privileges required, no user interaction, and high impact on confidentiality, integrity, and availability. Although no public exploits have been observed, the critical nature and ease of exploitation make this a significant threat to any web application using vulnerable AdonisJS versions. 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 relying on AdonisJS should prioritize updating and review multipart file upload handling to prevent exploitation.

For European organizations, this vulnerability poses a severe risk to web applications built on AdonisJS, especially those handling sensitive data or critical services. Successful exploitation can lead to arbitrary file writes, enabling attackers to deploy web shells, manipulate application logic, exfiltrate data, or disrupt services. This can result in data breaches, loss of service availability, reputational damage, and regulatory non-compliance under GDPR. Given the widespread use of Node.js and TypeScript in European tech sectors, including fintech, e-commerce, and public services, the impact could be broad. Attackers could leverage this vulnerability to pivot within networks, escalate privileges, or conduct ransomware attacks. The lack of required authentication and user interaction increases the risk of automated exploitation campaigns targeting vulnerable servers. Organizations with exposed web servers or APIs using vulnerable AdonisJS versions are particularly at risk.

1. Immediately upgrade @adonisjs/bodyparser to version 10.1.2 or later, or 11.0.0-next.6 or later for prerelease users. 2. Implement strict validation and sanitization of file upload paths to ensure no directory traversal sequences (e.g., '../') are accepted. 3. Employ runtime application self-protection (RASP) or web application firewalls (WAFs) with rules to detect and block suspicious multipart requests attempting path traversal. 4. Restrict file system permissions for the application process to the minimum necessary directories to limit damage from arbitrary writes. 5. Conduct thorough code reviews and penetration testing focused on file upload functionality. 6. Monitor logs for unusual file write activities or access to sensitive paths. 7. Educate developers on secure file handling practices and keep dependencies up to date. 8. Consider containerization or sandboxing to isolate the application environment and reduce attack surface.