Security: Prototype Pollution via Custom Attributes in BearerTokenType#440
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In `BearerTokenType.valueOf()`, custom attributes are iterated using `for...in` without proper prototype chain protection. While `Object.prototype.hasOwnProperty.call` is used, if `customAttributes` itself is an object with a polluted prototype (e.g., via `__proto__` or `constructor`), properties from the prototype chain could be included in the token response. Additionally, the constructor allows `customAttributes` to be any object, which could lead to information disclosure or unexpected behavior if malicious properties are passed. Signed-off-by: tomaioo <203048277+tomaioo@users.noreply.github.com>
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Dear @tomaioo if you think this is related to a reproducible vulnerability then please open a new advisory: https://github.com/node-oauth/node-oauth2-server/security/advisories/new |
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Summary
Security: Prototype Pollution via Custom Attributes in BearerTokenType
Problem
Severity:
Medium| File:lib/token-types/bearer-token-type.js:L58In
BearerTokenType.valueOf(), custom attributes are iterated usingfor...inwithout proper prototype chain protection. WhileObject.prototype.hasOwnProperty.callis used, ifcustomAttributesitself is an object with a polluted prototype (e.g., via__proto__orconstructor), properties from the prototype chain could be included in the token response. Additionally, the constructor allowscustomAttributesto be any object, which could lead to information disclosure or unexpected behavior if malicious properties are passed.Solution
Use
Object.keys(this.customAttributes)instead offor...into avoid prototype chain iteration, or ensurecustomAttributesis created withObject.create(null). Also validate thatcustomAttributesonly contains expected types (strings, numbers, booleans) to prevent object injection attacks.Changes
lib/token-types/bearer-token-type.js(modified)