Qwik is a performance-focused JavaScript framework. Versions prior to 1.19.2 improperly inferred arrays from dotted form field names during FormData parsing. By submitting mixed array-index and object-property keys for the same path, an attacker could cause user-controlled properties to be written onto values that application code expected to be arrays. When processing application/x-www-form-urlencoded or multipart/form-data requests, Qwik City converted dotted field names (e.g., items.0, items.1) into nested structures. If a path was interpreted as an array, additional attacker-supplied keys on that path—such as items.toString, items.push, items.valueOf, or items.length—could alter the resulting server-side value in unexpected ways, potentially leading to request handling failures, denial of service through malformed array state or oversized lengths, and type confusion in downstream code. This issue was fixed in version 1.19.2.

Affected: npm: @builder.io/qwik-city

**Summary**

Qwik City improperly inferred arrays from dotted form field names during `FormData` parsing. By submitting mixed array-index and object-property keys for the same path, an attacker could cause user-controlled properties to be written onto values that application code expected to be arrays.

**Description**

When processing `application/x-www-form-urlencoded` or `multipart/form-data` requests, Qwik City converted dotted field names such as `items.0` and `items.1` into nested structures. If a path was interpreted as an array, additional attacker-controlled keys on the same path, such as `items.toString`, `items.push`, `items.valueOf`, or `items.length`, could alter the resulting server-side value in unexpected ways.

Applications that assumed these parsed values were safe arrays could be affected. Depending on application behavior, this could lead to request handling failures, denial of service through malformed array state or oversized lengths, and type confusion in downstream code.

This issue affects form parsing in Qwik City request handling. It does not require authentication if the vulnerable route is publicly reachable.

**Impact**

An attacker can send crafted form submissions that cause parsed input to differ from the application’s expected shape. Possible outcomes include: - Triggering runtime errors when application code calls array methods on attacker-influenced values - Inflating array length or otherwise creating malformed structures that increase se…