Seroval: Code injection through a typed array's own constructor property

Summary

seroval writes a typed array as a call to its constructor. In affected versions, the constructor name in the output is read from a property that data on the value can replace, and it is written without checks. A typed array that received properties from untrusted data can then put arbitrary code into the serialized output.

Details

Version 1.6.0 changed how seroval finds the class of an object, so that objects with their own constructor property serialize correctly. Typed arrays still took the constructor name from the value itself, so the name could come from the untrusted property instead of the array's real type.

These functions are affected:

• serialize, serializeAsync
• crossSerialize, crossSerializeAsync, crossSerializeStream
• the Serializer class
• compileJSON

fromJSON and fromCrossJSON are not affected: they only accept the names of the built-in typed arrays. With the compactArrayBufferViews option, the same lookup throws a TypeError instead of writing code.

Impact

An application is affected only when it serializes a typed array that has an own constructor property set from untrusted data. That requires code that copies properties from untrusted objects onto a typed array. This is unusual, so the severity is rated Low, even though the result is script execution in the page that receives the output.

Patches

Fixed in 1.6.11. The constructor name now comes from the array's internal type, which properties on the value cannot change. compactArrayBufferViews uses the real type as well.

Workarounds

If you cannot upgrade, do not copy properties from untrusted objects onto typed arrays, or remove an own constructor property from a typed array before serializing it.