New HighSeverity Vulnerabilities in React Server Components & Next.js

Following the critical “React2Shell” disclosure earlier this month, three additional vulnerabilities were identified in React Server Components (RSC). These new flaws, carry high severity and widespread impact, requiring immediate developer action. As these new flaws allow an attacker to cause Denial of Service (DoS) or leak server-side source code. 

Affected Environments: 

• Core packages:  

• react-server-dom-webpack 

• react-server-dom-parcel 

• react-server-dom-turbopack 

• Frameworks/tools using RSC:  

• Next.js (App Router) 

• Waku 

• React Router 

Vulnerabilities: 

CVE202555184 and CVE202567779: Incomplete Patch → Denial of Service (DoS) 

• Impact: Crafted HTTP requests targeting App Router or Server Function endpoints cause infinite loops upon deserialization, hanging server processes and blocking future requests. 

• Severity: High (CVSS 7.5/10).  

• Details: A patch bypass vulnerability allows exploitation of the earlier DoS vector in patch versions 19.0.2, 19.1.3, and 19.2.2. As well as, a crafted HTTP requests targeting Server Function endpoints cause infinite loops during RSC deserialization, consuming CPU and hanging processes. 

CVE202555183: Source Code Exposure 

• Impact: Specific HTTP requests can trigger Server Functions to return compiled source code of any such functions, potentially revealing business logic and exposing hardcoded secrets. 

• Severity: Medium (CVSS 5.3/10). 

Mitigation and Remediation 

 Upgrade Immediately to patched versions: 

• Next.js versions (App Router only): 

  Re-patch even if previously updated: for React2Shell: the earlier fix was incomplete, so prior upgrades must be followed by this new update.  

  Verify environment hygiene: Ensure secrets are injected via environment variables and not hardcoded in server functions to mitigate source-code leaks. 

  Monitor systems for DoS symptoms: infinite loops, stalled endpoints. 

  Audit network activity: Look for unusual HTTP requests to App Router endpoints. 

If you are worried about any of the threats outlined in this bulletin or need help in determining what steps you should take to protect yourself from the most material threats facing your organisation, please contact your account manager, or alternatively Get in touch to find out how you can protect your organisation.