CVE-2026-30939: Parse Server DOS Vulnerability

CVE-2026-30939 Overview

Parse Server, an open source backend that can be deployed to any infrastructure running Node.js, contains a critical prototype pollution vulnerability that allows unauthenticated attackers to crash the server process. Prior to versions 8.6.13 and 9.5.1-alpha.2, an attacker can exploit the Cloud Function endpoint by supplying a prototype property name as the function name, causing infinite recursion that terminates the Parse Server process with a call stack size error.

Critical Impact

Unauthenticated remote attackers can cause complete denial of service by crashing Parse Server processes through prototype pollution in Cloud Function endpoint requests.

Affected Products

• Parse Server versions prior to 8.6.13
• Parse Server versions 9.x prior to 9.5.1-alpha.2
• All Parse Server deployments exposing the Cloud Function endpoint

Discovery Timeline

• 2026-03-10 - CVE-2026-30939 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2026-30939

Vulnerability Analysis

This vulnerability stems from improper handling of prototype property names in the Cloud Function dispatch mechanism. When an attacker sends a request to the Cloud Function endpoint using JavaScript prototype property names (such as __proto__, constructor, or prototype) as the function name, the server fails to properly validate the input before processing. This causes the server to enter an infinite recursion loop as it attempts to resolve the function through the prototype chain, ultimately exhausting the call stack and crashing the Node.js process.

The flaw is classified under CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes), commonly known as prototype pollution. The vulnerability affects the availability and integrity of the application since attackers can not only crash the server but also bypass Cloud Function dispatch validation entirely. Certain prototype property names return HTTP 200 responses even when no corresponding Cloud Functions are defined, which could be leveraged for further reconnaissance or exploitation.

Root Cause

The root cause is insufficient input validation in the Cloud Function dispatch logic. The server does not sanitize or reject requests where the function name corresponds to built-in JavaScript prototype properties. When these reserved property names are used, the server's lookup mechanism traverses the object prototype chain instead of the defined Cloud Functions, leading to uncontrolled recursion or unexpected behavior. The same vulnerability applies to dot-notation traversal patterns, allowing attackers to access prototype properties through nested path references.

Attack Vector

This vulnerability is exploitable remotely over the network without any authentication requirements. An attacker simply needs to send a crafted HTTP request to the Cloud Function endpoint with a malicious function name parameter. The attack requires no user interaction and has low complexity, making it highly accessible to unsophisticated attackers. The primary impact is availability loss through process termination, though the validation bypass could also enable integrity violations.

The attack can be executed by sending requests such as calling the Cloud Function endpoint with function names like __proto__, constructor.prototype, or similar JavaScript prototype chain properties. When the server processes these requests, it fails to recognize them as invalid function names and instead follows the prototype chain, causing the infinite recursion that crashes the process.

Detection Methods for CVE-2026-30939

Indicators of Compromise

• Unexpected Parse Server process crashes with call stack size exceeded errors
• HTTP requests to Cloud Function endpoints containing prototype property names (__proto__, constructor, prototype)
• Anomalous HTTP 200 responses from Cloud Function endpoints for undefined function names
• Repeated process restarts or service availability issues without clear cause
• Log entries showing requests with dot-notation traversal patterns targeting prototype properties

Detection Strategies

• Monitor application logs for call stack overflow exceptions and unexpected process terminations
• Implement Web Application Firewall (WAF) rules to block requests containing prototype property names in function parameters
• Configure intrusion detection systems to alert on patterns matching __proto__, constructor, or prototype in request URIs and body content
• Review Parse Server access logs for Cloud Function calls with suspicious function names

Monitoring Recommendations

• Set up automated alerting for Parse Server process crashes and restarts
• Implement application performance monitoring to detect service availability degradation
• Enable detailed request logging for Cloud Function endpoints to capture malicious request patterns
• Monitor system resources for signs of denial of service attempts such as CPU spikes before process termination

How to Mitigate CVE-2026-30939

Immediate Actions Required

• Upgrade Parse Server to version 8.6.13 or later for the stable branch
• Upgrade Parse Server to version 9.5.1-alpha.2 or later for the alpha branch
• Implement WAF rules to filter requests containing prototype pollution patterns as a temporary measure
• Review and restrict network access to Cloud Function endpoints if possible

Patch Information

Parse Platform has released security patches addressing this vulnerability. The fix is available in Parse Server Release 8.6.13 for stable deployments and Parse Server Release 9.5.1-alpha.2 for alpha deployments. Organizations should upgrade to these versions immediately. For full details on the vulnerability and remediation, refer to the GitHub Security Advisory GHSA-5j86-7r7m-p8h6.

Workarounds

• Deploy a reverse proxy or WAF in front of Parse Server to filter requests containing __proto__, constructor, or prototype in function name parameters
• Implement rate limiting on Cloud Function endpoints to reduce the impact of repeated crash attempts
• Configure process managers like PM2 or systemd to automatically restart Parse Server processes while patches are being applied
• Consider temporarily disabling or restricting access to Cloud Function endpoints if they are not critical to operations

# Example nginx configuration to block prototype pollution attempts
location /parse/functions/ {
    if ($request_uri ~* "__proto__|constructor|prototype") {
        return 403;
    }
    proxy_pass http://parse-server:1337;
}