CVE-2025-55183: Facebook React Information Disclosure Flaw

CVE-2025-55183 Overview

An information leak vulnerability has been identified in React Server Components that allows attackers to extract the source code of Server Functions through specially crafted HTTP requests. This source code disclosure vulnerability affects multiple React version 19 releases and associated bundler packages including react-server-dom-parcel, react-server-dom-turbopack, and react-server-dom-webpack. The vulnerability requires the existence of a Server Function that explicitly or implicitly exposes a stringified argument, enabling remote attackers to retrieve sensitive server-side code without authentication.

Critical Impact

Attackers can remotely retrieve Server Function source code, potentially exposing business logic, API keys, database queries, and other sensitive implementation details embedded in server-side React components.

Affected Products

• Facebook React versions 19.0.0, 19.0.1, 19.1.0, 19.1.1, 19.1.2, 19.2.0, and 19.2.1
• Vercel Next.js versions 15.6.0 (including canary releases) and 16.1.0 (including canary releases)
• React Server DOM packages: react-server-dom-parcel, react-server-dom-turbopack, react-server-dom-webpack

Discovery Timeline

• December 11, 2025 - CVE-2025-55183 published to NVD
• December 12, 2025 - Last updated in NVD database

Technical Details for CVE-2025-55183

Vulnerability Analysis

This source code disclosure vulnerability exploits improper handling of Server Function arguments in React Server Components. When a Server Function stringifies an argument (either explicitly through methods like JSON.stringify() or implicitly through type coercion), the internal mechanism that processes these arguments can be manipulated to return the function's source code instead of executing the intended operation.

The vulnerability is particularly concerning because Server Functions often contain sensitive implementation details including database connection strings, API endpoints, authentication logic, and business-critical algorithms. Successful exploitation provides attackers with a blueprint of the application's server-side architecture, facilitating further attacks.

Root Cause

The root cause lies in insufficient input validation within the Server Function request handler. When processing incoming HTTP requests to Server Functions, the system fails to properly sanitize and validate the structure of function arguments. Specifically, when arguments are expected to be stringified, the parsing logic can be tricked into reflecting the source code of the target function rather than processing legitimate input data.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending malformed HTTP requests to endpoints that handle Server Function invocations. The attack requires identifying Server Functions that process stringified arguments, which can often be discovered through application reconnaissance or error message analysis. Once a vulnerable endpoint is identified, the attacker crafts a request that triggers the information leak, causing the server to respond with the complete source code of the targeted Server Function.

The vulnerability affects applications using specific React Server DOM bundler integrations, meaning applications deployed with Parcel, Turbopack, or Webpack bundlers that utilize React Server Components are potentially at risk.

Detection Methods for CVE-2025-55183

Indicators of Compromise

• Unusual HTTP requests targeting Server Function endpoints with malformed or unexpected argument structures
• Server responses containing JavaScript source code in API responses where data payloads are expected
• Increased reconnaissance activity against application endpoints, particularly those handling Server Actions
• Log entries showing repeated requests to the same Server Function endpoints with varying argument formats

Detection Strategies

• Monitor web server logs for requests to Server Function endpoints containing unusual or malformed payloads
• Implement content-type validation to detect responses inadvertently returning JavaScript source code
• Deploy Web Application Firewall (WAF) rules to identify and block requests with suspicious argument structures
• Review application logs for error patterns indicating argument parsing failures in Server Functions

Monitoring Recommendations

• Enable verbose logging on React Server Component request handlers to capture detailed request information
• Set up alerting for anomalous response sizes from Server Function endpoints that may indicate source code exposure
• Monitor for scanning activity targeting common Server Action endpoint patterns
• Implement runtime application self-protection (RASP) to detect and block information disclosure attempts

How to Mitigate CVE-2025-55183

Immediate Actions Required

• Upgrade React to a patched version as specified in the official security advisory
• Audit all Server Functions for patterns that stringify arguments and apply additional input validation
• Review server logs for evidence of exploitation attempts against Server Function endpoints
• Consider temporarily disabling affected Server Functions until patches can be applied

Patch Information

Facebook and Vercel have released security advisories addressing this vulnerability. Organizations should consult the React Blog Post on Security Issues and the Facebook Security Advisory CVE-2025-55183 for specific patched versions and upgrade instructions. Applications using Next.js should also update to patched versions of the framework.

Workarounds

• Implement request validation middleware to sanitize and validate all incoming Server Function arguments before processing
• Add explicit type checking and validation for all Server Function parameters to prevent argument manipulation
• Deploy network-level controls such as rate limiting and request filtering on Server Function endpoints
• Consider implementing server-side request logging with anomaly detection to identify exploitation attempts

# Verify current React version and check for vulnerable packages
npm list react react-server-dom-webpack react-server-dom-parcel react-server-dom-turbopack

# Update React to the latest patched version
npm update react react-dom react-server-dom-webpack

# For Next.js applications, update to patched version
npm update next