CVE-2025-67779: Facebook React DoS Vulnerability

CVE-2025-67779 Overview

CVE-2025-67779 is an Insecure Deserialization vulnerability affecting React Server Components that allows attackers to cause a denial of service through specially crafted HTTP requests. This vulnerability represents an incomplete fix for CVE-2025-55184, where the original patch failed to prevent a denial of service attack in a specific case. The flaw enables unsafe deserialization of payloads sent to Server Function endpoints, which can trigger an infinite loop that hangs the server process and prevents future HTTP requests from being served.

Critical Impact

Unauthenticated attackers can remotely cause complete server unavailability by sending malicious payloads to Server Function endpoints, resulting in an infinite loop that hangs the Node.js process.

Affected Products

• Facebook React versions 19.0.2, 19.1.3, and 19.2.2
• Vercel Next.js 15.6.0 (including all canary releases)
• Vercel Next.js 16.1.0 (including all canary releases)

Discovery Timeline

• December 12, 2025 - CVE-2025-67779 published to NVD
• December 12, 2025 - Last updated in NVD database

Technical Details for CVE-2025-67779

Vulnerability Analysis

This vulnerability stems from inadequate input validation during the deserialization of incoming HTTP request payloads destined for React Server Function endpoints. When React Server Components processes certain malformed payloads, the deserialization logic enters a state where it becomes trapped in an infinite loop. This effectively freezes the Node.js event loop, causing the server to become unresponsive to all subsequent requests.

The vulnerability is particularly concerning because it requires no authentication or special privileges to exploit. Any network-accessible React Server Components deployment is potentially at risk, and a single malicious request can render the entire application unavailable until the process is manually restarted.

Root Cause

The root cause lies in the incomplete remediation of CVE-2025-55184. The original patch addressed the primary deserialization vulnerability but failed to account for an edge case that allows specially crafted payloads to bypass the fix. The deserialization routine lacks proper termination conditions or recursion depth limits when processing certain payload structures, enabling attackers to construct inputs that cause unbounded processing.

Attack Vector

An attacker can exploit this vulnerability by sending a crafted HTTP POST request to any Server Function endpoint. The payload must be structured in a way that triggers the specific edge case not covered by the CVE-2025-55184 fix. Since Server Functions are a core feature of React Server Components and are commonly exposed to handle form submissions and other user interactions, the attack surface is broad across modern React applications using this architecture.

The attack requires no authentication and can be executed remotely by any client capable of sending HTTP requests to the target server. Once the malicious payload is processed, the server enters an infinite loop, consuming CPU resources and blocking the event loop, which prevents any other requests from being processed.

Detection Methods for CVE-2025-67779

Indicators of Compromise

• Sudden spike in CPU utilization on servers running React Server Components applications
• Server processes becoming unresponsive without crashing or generating error logs
• Accumulated pending HTTP requests in load balancer or proxy queues
• Application health check failures without corresponding application-level errors

Detection Strategies

• Monitor Node.js process CPU usage for sustained 100% utilization patterns that indicate infinite loop conditions
• Implement request timeout monitoring to detect requests that exceed normal processing duration thresholds
• Configure application performance monitoring (APM) to alert on event loop blocking events
• Review HTTP access logs for unusual POST requests to Server Function endpoints with atypical payload sizes or patterns

Monitoring Recommendations

• Deploy real-time alerting for CPU saturation on application servers running React applications
• Implement health check endpoints that verify event loop responsiveness, not just process availability
• Configure load balancers to detect and remove unresponsive backend instances from rotation
• Enable detailed request logging for Server Function endpoints to facilitate post-incident analysis

How to Mitigate CVE-2025-67779

Immediate Actions Required

• Upgrade React to a patched version that fully addresses this vulnerability
• Review the React Security Advisory for vendor-specific guidance
• Upgrade Next.js to a patched version if using Vercel's framework
• Implement request rate limiting on Server Function endpoints as a temporary defense

Patch Information

Facebook has released security advisories detailing the vulnerability and remediation steps. Organizations should consult the Facebook Security Advisory for CVE-2025-67779 for the latest patched versions of React. Next.js users should similarly check for updated releases that incorporate the React fix.

Workarounds

• Deploy a Web Application Firewall (WAF) with rules to inspect and sanitize payloads before they reach Server Function endpoints
• Implement request timeout enforcement at the reverse proxy or load balancer level to terminate long-running requests
• Use process managers like PM2 or systemd with automatic restart capabilities to recover from hung processes
• Consider temporarily disabling Server Functions if they are not critical to application functionality until patching can be completed

# Example: Configure request timeout in Nginx as a mitigation layer
# Add to nginx.conf server or location block for Server Function routes
proxy_read_timeout 30s;
proxy_connect_timeout 10s;
proxy_send_timeout 30s;

# Example: PM2 configuration for automatic restart on unresponsive process
# ecosystem.config.js
# max_memory_restart: '500M'
# restart_delay: 3000
# max_restarts: 10