CVE-2026-25754: AdonisJS Prototype Pollution Vulnerability

CVE-2026-25754 Overview

CVE-2026-25754 is a prototype pollution vulnerability affecting AdonisJS, a TypeScript-first web framework. The vulnerability exists in the multipart form-data parsing component of the AdonisJS bodyparser module, allowing remote attackers to manipulate JavaScript object prototypes at runtime through specially crafted HTTP requests.

Prototype pollution is a class of vulnerabilities specific to JavaScript-based applications where an attacker can modify the prototype of base objects like Object.prototype. This can lead to application-wide security implications including authentication bypass, denial of service, and in some cases remote code execution depending on how the polluted properties are used downstream.

Critical Impact

Remote attackers can manipulate object prototypes through malicious multipart form-data requests, potentially affecting application behavior, bypassing security controls, or causing denial of service across the entire AdonisJS application.

Affected Products

• AdonisJS bodyparser versions prior to 10.1.3
• AdonisJS bodyparser versions prior to 11.0.0-next.9

Discovery Timeline

• 2026-02-06 - CVE-2026-25754 published to NVD
• 2026-02-09 - Last updated in NVD database

Technical Details for CVE-2026-25754

Vulnerability Analysis

This vulnerability is classified under CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes). The flaw resides in how the AdonisJS bodyparser module processes multipart form-data submissions. When parsing incoming HTTP requests with multipart content, the parser fails to properly sanitize field names, allowing attackers to inject prototype pollution payloads.

The attack is network-based and requires no authentication or user interaction to exploit. An attacker can send crafted multipart form-data requests containing malicious field names such as __proto__, constructor, or prototype with arbitrary values. These values are then inadvertently assigned to the prototype chain of JavaScript objects, affecting all objects that inherit from the polluted prototype.

The impact includes potential confidentiality and integrity breaches across the affected application. Depending on how the application uses objects downstream, this could manifest as security control bypasses, unexpected application behavior, or information disclosure.

Root Cause

The root cause of this vulnerability is inadequate input validation in the multipart form-data parsing logic. The bodyparser module directly uses user-supplied field names as object property keys without filtering dangerous prototype-related properties. This allows specially crafted field names to modify the prototype chain rather than creating standard object properties.

JavaScript's prototype-based inheritance model means that modifications to Object.prototype propagate to all objects in the application, making this a particularly impactful vulnerability class in Node.js applications.

Attack Vector

The attack vector is network-based, exploiting HTTP multipart form-data requests. An attacker constructs a malicious HTTP POST request with Content-Type: multipart/form-data containing field names designed to target prototype properties.

When the vulnerable bodyparser processes this request, instead of creating a normal form field, it modifies the object prototype. Any subsequent code that checks for the existence of the polluted property or uses its value may behave unexpectedly.

For example, if an attacker pollutes a property used in authentication checks (such as isAdmin), the application might grant elevated privileges. If a property used in template rendering is polluted, it could lead to information disclosure or injection attacks.

For detailed technical information about this vulnerability and the specific code changes, refer to the GitHub Security Advisory GHSA-f5x2-vj4h-vg4c and the commit that addresses this issue.

Detection Methods for CVE-2026-25754

Indicators of Compromise

• HTTP requests containing suspicious field names such as __proto__, constructor.prototype, or prototype in multipart form-data payloads
• Unexpected properties appearing on JavaScript objects that were not explicitly set by application code
• Anomalous application behavior following multipart form submissions
• Web application firewall logs showing blocked requests with prototype pollution patterns

Detection Strategies

• Deploy web application firewall rules to detect and block multipart requests containing __proto__, constructor, or prototype in field names
• Implement application-level logging to capture and alert on suspicious form field names during request parsing
• Use runtime application self-protection (RASP) solutions to monitor for prototype modifications at runtime
• Configure SentinelOne Singularity to monitor Node.js applications for anomalous object prototype access patterns

Monitoring Recommendations

• Enable detailed access logging on web servers and reverse proxies to capture full request bodies for forensic analysis
• Monitor application error rates and unexpected behavior patterns that may indicate successful exploitation
• Set up alerts for unusual traffic patterns targeting endpoints that accept multipart form-data
• Review application logs for JavaScript errors that may indicate prototype pollution side effects

How to Mitigate CVE-2026-25754

Immediate Actions Required

• Update AdonisJS bodyparser to version 10.1.3 or later for the stable branch
• Update AdonisJS bodyparser to version 11.0.0-next.9 or later for the next branch
• Audit application code for any custom multipart parsing logic that may have similar vulnerabilities
• Deploy WAF rules to block prototype pollution attempts while patching is in progress

Patch Information

The AdonisJS team has released patched versions that address this prototype pollution vulnerability. The fix involves sanitizing field names during multipart form-data parsing to prevent prototype-related properties from being processed.

• Stable Branch Fix: Version 10.1.3 - GitHub Release v11.0.0-next.9
• Next Branch Fix: Version 11.0.0-next.9
• Commit Reference:40e1c71f958cffb74f6b91bed6630dca979062ed

For complete details on the vulnerability and remediation, see the GitHub Security Advisory GHSA-f5x2-vj4h-vg4c.

Workarounds

• Implement middleware to sanitize incoming request field names before they reach the bodyparser, stripping __proto__, constructor, and prototype properties
• Use Object.create(null) for objects that store user-supplied data to create objects without a prototype chain
• Deploy a reverse proxy or WAF with rules to filter requests containing prototype pollution payloads in multipart form-data
• Consider using Object.freeze(Object.prototype) in non-production environments for testing, though this may break some legitimate functionality

# Update AdonisJS bodyparser to patched version
npm update @adonisjs/bodyparser@10.1.3

# Or for next branch users
npm update @adonisjs/bodyparser@11.0.0-next.9

# Verify installed version
npm list @adonisjs/bodyparser