CVE-2026-44483: RVF Prototype Pollution Vulnerability

CVE-2026-44483 Overview

CVE-2026-44483 is a prototype pollution vulnerability in RVF (formerly Remix Validated Form), a form validation and state management library for React. The flaw resides in the setPath function within @rvf/set-get, which @rvf/core uses to flatten incoming form data into nested objects. The function fails to block the dangerous keys __proto__, constructor, and prototype when walking a path. Attackers who submit a form to any Remix or React Router application using affected RVF versions can set arbitrary properties on Object.prototype of the server process. The vulnerability affects versions 6.0.0 through 6.0.3 and 7.0.0 through 7.0.1.

Critical Impact
Unauthenticated attackers can pollute Object.prototype on the server by submitting crafted form data to any endpoint using parseFormData or a validator created with createValidator.

Affected Products

RVF (@rvf/core, @rvf/set-get) versions 6.0.0 to 6.0.3
RVF (@rvf/core, @rvf/set-get) versions 7.0.0 to 7.0.1
Remix and React Router applications using affected RVF versions for form processing

Discovery Timeline

2026-05-27 - CVE-2026-44483 published to NVD
2026-05-27 - Last updated in NVD database

Technical Details for CVE-2026-44483

Vulnerability Analysis

The vulnerability is a prototype pollution flaw classified under [CWE-1321] (Improperly Controlled Modification of Object Prototype Attributes). RVF processes submitted form data by mapping flat field names like user[profile][name] into nested JavaScript objects. The setPath helper in @rvf/set-get walks each path segment and assigns values to the corresponding object property. The implementation does not filter the reserved keys __proto__, constructor, or prototype. As a result, a field name such as __proto__[polluted] causes the assignment to traverse into Object.prototype and set a property visible on every object in the running Node.js process.

Root Cause

Field names from submitted form data flow directly into setPath through preprocessFormData, which is called by both parseFormData and validators built with createValidator. No sanitization or allow-list filtering is applied to path segments before traversal. The library treats attacker-controlled keys as trusted property names.

Attack Vector

The attack is network-reachable and requires no authentication, user interaction, or special configuration. Any HTTP endpoint that accepts a form and calls parseFormData or runs an RVF validator is exposed. An attacker submits a multipart or URL-encoded form containing a crafted field name targeting __proto__ or constructor.prototype, and the polluted property persists on Object.prototype for the lifetime of the process. Downstream code that reads properties from plain objects without hasOwnProperty checks may then take attacker-controlled branches, enabling authentication bypass, logic flaws, or denial of service depending on the application.

Detection Methods for CVE-2026-44483

Indicators of Compromise

Form submissions containing field names with __proto__, constructor, or prototype segments in request bodies or query strings.
Unexpected properties appearing on plain JavaScript objects at runtime, such as a global flag set without an originating assignment.
Anomalous behavior changes in Node.js server processes following form POST requests, including unexplained authorization decisions or feature toggles.

Detection Strategies

Inspect HTTP request logs and Web Application Firewall (WAF) logs for form field names containing __proto__, constructor[prototype], or URL-encoded equivalents like %5F%5Fproto%5F%5F.
Audit installed dependency versions of @rvf/core and @rvf/set-get using npm ls @rvf/core @rvf/set-get and flag versions below 6.0.4 or 7.0.2.
Add runtime assertions in non-production environments that detect mutations to Object.prototype and alert on unexpected enumerable keys.

Monitoring Recommendations

Forward Node.js application logs and reverse proxy logs to a centralized analytics platform and alert on requests containing prototype pollution payloads.
Track dependency manifests in source control and trigger alerts when affected RVF versions are introduced or remain unpatched.
Monitor for crashes, unexpected 500 responses, or behavioral changes following form submissions, which can indicate successful pollution.

How to Mitigate CVE-2026-44483

Immediate Actions Required

Upgrade @rvf/core and @rvf/set-get to version 6.0.4 if running the 6.x branch, or to 7.0.2 if running the 7.x branch.
Audit all routes that call parseFormData or use validators returned by createValidator and treat them as exposed until patched.
Restart the Node.js process after patching to clear any properties already set on Object.prototype.

Patch Information

The maintainers fixed CVE-2026-44483 in @rvf/set-get 6.0.4 and 7.0.2 by blocking the reserved keys __proto__, constructor, and prototype during path traversal in setPath. Refer to the GitHub Security Advisory GHSA-c567-44rc-m5hq for the upstream fix details.

Workarounds

Reject incoming requests at a WAF or reverse proxy layer when field names contain __proto__, constructor, or prototype substrings (including URL-encoded forms).
Wrap parseFormData calls with a pre-filter that strips form fields whose keys include reserved prototype names before they reach RVF.
Freeze Object.prototype at application startup using Object.freeze(Object.prototype) to prevent runtime mutation, after testing for compatibility with all dependencies.

bash

# Upgrade to patched RVF versions
npm install @rvf/core@^7.0.2 @rvf/set-get@^7.0.2
# Or for the 6.x branch
npm install @rvf/core@^6.0.4 @rvf/set-get@^6.0.4

# Verify installed versions
npm ls @rvf/core @rvf/set-get