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.

Seroval facilitates JavaScript value stringification, including complex structures beyond JSON.stringify capabilities. Prior to 1.0.0 and from 1.5.5 until 1.6.10, the JavaScript-output APIs serialize a RegExp source containing a less-than character without the escaping needed for an HTML script element. An application is affected when it builds regular expression syntax from untrusted input, serializes that RegExp through serialize, serializeAsync, crossSerialize, crossSerializeAsync, crossSerializeStream, Serializer, or compileJSON, and embeds the result in an HTML script element. The crafted source can terminate the element and execute script in the page received by another user. This issue is fixed in version 1.6.10.

Seroval deserializes typed arrays without validating their buffers, allowing malicious payloads to exhaust server resources or invoke registered functions.

A fulfilled Promise node deserialized by fromJSON() can trigger unintended invocation of a plugin-produced callable through native ECMAScript thenable assimilation. This bypasses the type-confusion fix in seroval@1.5.3 (GHSA-mv8w-475r-vwqw / CVE-2026-59940) and affects every plugin-capable release from 0.12.0 through the current 1.6.0.

Summary

deserializeTypedArray casts the source node to ArrayBuffer without checking it and never bounds the element count. Pass a plain object with a length property and it hits the array-like TypedArray constructor, allocating that many elements. The offset guard above it can't stop this: source.byteLength is undefined, so the comparison is always false.

The length is one integer in the JSON, so a tiny payload can name any allocation size, and it runs synchronously inside fromJSON, starving the event loop instead of just slowing one request. fromCrossJSON is the same.

Impact is unauthenticated CPU/memory exhaustion for any service deserializing untrusted Seroval JSON: same profile as the array-length and nested-depth DoS issues already fixed here. No confidentiality or integrity impact. DataView has the same unchecked cast but throws instead of allocating. A runtime instanceof ArrayBuffer check plus a size cap should fix it.

Serialization of objects with extreme depth can exceed the maximum call stack limit.

Mitigation: Seroval introduces a depthLimit parameter in serialization/deserialization methods. An error will be thrown if the depth limit is reached.