Affected: CleanStart: n8n

Security vulnerability affects the n8n package. This issue is resolved in later releases. See references for vulnerability details.

protobufjs compiles protobuf definitions into JavaScript (JS) functions. From 8.2.0 until 8.6.5, the protobufjs Text Format extension parsed string-keyed map entries using ordinary property assignment, allowing a map entry with key __proto__ to change the prototype of the returned map object instead of creating an own map entry in protobufjs/ext/textformat. This issue is fixed in version 8.6.5.

Affected: npm: protobufjs

## Summary

The protobuf.js text format extension parsed string-keyed map entries using ordinary property assignment. A text-format map entry with key `__proto__` could therefore change the prototype of the returned map object instead of creating an own map entry.

This affected the optional Text Format extension. Other protobufjs input paths, including binary decode, `fromObject`, and ProtoJSON conversion, are not affected.

## Impact

An attacker who can provide protobuf text-format input parsed by an application using `protobufjs/ext/textformat` may be able to create message objects whose string-keyed map fields have attacker-controlled prototypes.

This is per-object prototype mutation, not global `Object.prototype` pollution. Impact depends on downstream application logic treating inherited properties as meaningful, for example by using `in`, truthiness checks, or direct property access on parsed map objects instead of own-property checks.

Applications that do not parse untrusted Text Format input, or that do not use inherited properties from parsed map objects in security-relevant logic, are not directly affected.

## Preconditions

* The application must parse attacker-controlled protobuf Text Format input with `protobufjs/ext/textformat`. * The target schema must contain a string-keyed map field. * The crafted input must provide a map entry with key `__proto__`. * Downstream application logic must treat inherited properties on the returned map object as meaningful f…