A severe security vulnerability has been uncovered in the
@adonisjs/bodyparser
npm package, prompting an urgent call for developers to update their installations. This critical flaw, with a CVSS score of 9.2, could enable remote attackers to write arbitrary files onto affected servers, potentially leading to remote code execution (RCE).
The Path Traversal Threat: CVE-2026-21440
Tracked as CVE-2026-21440, the vulnerability is a classic path traversal issue embedded within the AdonisJS multipart file handling mechanism. AdonisJS, a popular Node.js framework for building web applications and API servers with TypeScript, relies on the @adonisjs/bodyparser library to process HTTP request bodies. The core of the problem lies in how the framework handles file uploads when developers utilize the MultipartFile.move() function.
How the Exploitation Unfolds
According to project maintainers, the vulnerability arises when a developer uses MultipartFile.move() without providing the second options argument or without explicitly sanitizing the filename. In such scenarios, an attacker can supply a specially crafted filename containing path traversal sequences (e.g., ../../). This malicious input allows the attacker to dictate a destination path outside the intended upload directory, leading to arbitrary file writes on the server.
The MultipartFile.move(location, options) function is designed to relocate an uploaded file. The options parameter typically includes a desired filename and an overwrite flag. The critical oversight occurs when the filename isn’t explicitly passed, causing the application to default to an unsanitized client-provided filename. If the overwrite flag is also set to true, an attacker gains the alarming ability to overwrite sensitive files at a location of their choosing.
The Grave Implications: From File Write to RCE
The consequences of successful exploitation are significant. While arbitrary file write itself is a serious concern, the potential for remote code execution (RCE) elevates this flaw to a critical level. AdonisJS developers warn, “If the attacker can overwrite application code, startup scripts, or configuration files that are later executed/loaded, RCE [remote code execution] is possible.”
It’s important to note that RCE isn’t guaranteed and depends on several factors, including filesystem permissions, the server’s deployment layout, and the application’s runtime behavior. However, the mere possibility underscores the urgency of patching this vulnerability.
Who is Affected and What to Do
The issue, discovered and responsibly reported by security researcher Hunter Wodzenski (@wodzen), impacts various versions of the @adonisjs/bodyparser package. Users are strongly advised to update to the latest available version of the package immediately to mitigate the risk. Updating ensures that the file handling mechanism properly sanitizes filenames, preventing path traversal attacks.
Developers should review their implementations of MultipartFile.move() to ensure that filenames are always explicitly sanitized or that the options argument is used correctly to prevent reliance on unsanitized client input. Proactive patching and secure coding practices are paramount in safeguarding web applications against such critical threats.
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