The library scim-patch applies SCIM PATCH operations without filtering keys that target prototype properties. When a patch includes a key such as "__proto__.someProp", the library sets Object.prototype.someProp in the running Node process. This prototype pollution propagates to all plain objects, potentially corrupting application data and enabling malicious code to be executed or privileges to be escalated. The flaw falls under CWE-1321 and is rated with a CVSS score of 9.1.

The vulnerability appears in all releases of the scim-patch library from thomaspoignant before version 0.9.1. Any Node.js application that imports this library and exposes a SCIM PATCH endpoint for external Identity Providers is affected. Version 0.9.1 and later contain the fix and are no longer vulnerable.

The high CVSS score reflects the serious impact; the EPSS score is not available, but the absence from the KEV catalog does not reduce the risk because the issue can be exploited by an attacker who can influence the SCIM PATCH payload. The likely attack vector is remote, through HTTP PATCH requests directed at the SCIM API. A single malicious patch can alter the process‑wide prototype and provide an attacker with an escape hatch into the application’s runtime.