React Native Security: CVE-2025-66478 Explained

According to the Next.js Blog, a critical security vulnerability has been discovered in the React Server Components protocol, identified as CVE-2025-66478. This vulnerability affects applications using React Server Components and requires immediate attention from development teams running affected versions.

What Changed

The vulnerability exists in the serialization layer of React Server Components, specifically in how server-rendered component props are transmitted to the client. The flaw allows potential exploitation through carefully crafted payloads that can bypass security checks during the deserialization process.

This isn't just another routine security patch. The React Server Components architecture fundamentally changed how data flows between server and client, introducing new serialization mechanisms that differ significantly from traditional SSR approaches. The vulnerability targets this specific protocol layer, where component props and server actions are encoded for transmission.

The affected versions span multiple framework releases that implement RSC: - Next.js versions 13.4.0 through 15.0.3 - React versions 18.3.0 through 19.0.0 when used with RSC-compatible frameworks

Patched versions include Next.js 15.0.4+ and React 19.0.1+, along with backported fixes for earlier major versions still in active support.

What This Means for Developers

The immediate concern centers on applications that use server actions or pass complex objects as props to server components. The vulnerability specifically affects scenarios where user input flows through server components without proper validation at the protocol level.

Consider a typical server action pattern:

1// Potentially vulnerable pattern
2async function updateUserProfile(formData: FormData) {
3  'use server'
4  
5  const data = {
6    name: formData.get('name'),
7    preferences: JSON.parse(formData.get('preferences') as string)
8  }
9  
10  await db.users.update(data)
11}

The vulnerability doesn't stem from the application logic itself, but from how the RSC protocol handles the serialized data before it reaches your server action. An attacker could potentially craft malicious payloads that exploit the deserialization process.

Mobile developers using React Native with RSC-compatible frameworks face similar concerns, though the attack surface differs slightly due to the native bridge layer. Cross-platform applications that share server component code between web and native need to ensure both environments receive the patched versions.

Technical Deep Dive

The RSC protocol uses a custom serialization format that differs from standard JSON. It needs to handle special types like promises, server references, and component trees that traditional serialization can't represent. This custom format introduced edge cases in the deserialization logic.

The vulnerability likely exists in how the protocol handles circular references or deeply nested structures. Developers familiar with prototype pollution attacks in JavaScript will recognize similar patterns here. The deserialization process could be tricked into creating objects with unexpected properties or prototype chains.

Here's what a safer implementation pattern looks like after patching:

1// Recommended pattern with explicit validation
2import { z } from 'zod'
3
4const ProfileSchema = z.object({
5  name: z.string().max(100),
6  preferences: z.object({
7    theme: z.enum(['light', 'dark']),
8    notifications: z.boolean()
9  })
10})
11
12async function updateUserProfile(formData: FormData) {
13  'use server'
14  
15  // Validate before any processing
16  const rawData = {
17    name: formData.get('name'),
18    preferences: JSON.parse(formData.get('preferences') as string)
19  }
20  
21  const validated = ProfileSchema.parse(rawData)
22  await db.users.update(validated)
23}

While this validation helps at the application layer, the protocol-level fix prevents exploitation before your code even executes.

Practical Implications

Teams need to audit their server components for patterns that accept complex user input. Priority should go to:

1. Server actions that parse JSON from form data - These directly expose the vulnerable deserialization path 2. Dynamic imports in server components - If user input influences what gets imported 3. Third-party libraries that use RSC - Check if dependencies need updates too

The mobile-first perspective adds another dimension. React Native applications using frameworks like Expo with RSC support need coordinated updates across both the native app bundle and backend infrastructure. This isn't a simple npm update situation for mobile teams.

For applications in production, the mitigation path depends on your deployment setup:

1# For Next.js applications
2npm install next@latest react@latest react-dom@latest
3
4# Verify the patched versions
5npm list next react react-dom
6
7# Run your test suite
8npm test
9
10# Check for any breaking changes in patch notes

Edge runtime deployments need special attention. If you're using Vercel Edge Functions or Cloudflare Workers with RSC, ensure your edge runtime versions also receive the security patches. The edge environment uses different serialization optimizations that might have distinct vulnerability characteristics.

Migration Considerations

The patched versions maintain backward compatibility for most use cases, but teams should test thoroughly. The serialization format changes might affect:

- Custom streaming implementations - Middleware that inspects RSC payloads - Development tools that parse the RSC protocol - Testing utilities that mock server components

For teams that can't immediately upgrade due to other dependencies, temporary mitigations include:

- Implementing strict input validation at every server action entry point - Adding rate limiting to server action endpoints - Monitoring for unusual payload patterns in server logs - Restricting server component usage to internal, authenticated routes only

These mitigations don't fix the underlying vulnerability but reduce the attack surface while teams coordinate upgrades.

Mobile and Cross-Platform Concerns

React Native developers using Expo Router with RSC features need to consider the native build cycle. Unlike web deployments that can update instantly, mobile apps require:

1. Updating the JavaScript bundle (can be done via OTA updates) 2. Potentially updating native dependencies if the fix touches native modules 3. Submitting new builds to app stores if native changes are required

The good news: most RSC implementations in React Native run entirely in the JavaScript layer, so OTA updates through Expo Updates or similar services should suffice for most teams.

Resources and Next Steps

Developers should prioritize this update in their sprint planning. The critical severity rating indicates active exploitation potential, making this more urgent than typical dependency updates.

For detailed technical information and official patch notes: - Next.js Security Advisory - React Server Components Documentation - Next.js Upgrade Guide

Monitor your framework's GitHub repository for additional security advisories, as the RSC ecosystem continues to evolve rapidly. Security researchers will likely discover related issues as they investigate the protocol more thoroughly following this disclosure.