DOM-based vulnerabilities arise when a client-side script reads data from a controllable part of the DOM (for example, the URL) and processes this data in an unsafe way.
DOM-based JSON injection arises when a script incorporates controllable data into a string that is parsed as a JSON data structure and then processed by the application. An attacker may be able to use this behavior to construct a URL that, if visited by another application user, will cause arbitrary JSON data to be processed. Depending on the purpose for which this data is used, it may be possible to subvert the application's logic, or cause unintended actions on behalf of the user.
Burp Suite automatically identifies this issue using static code analysis, which may lead to false positives that are not actually exploitable. The relevant code and execution paths should be reviewed to determine whether this vulnerability is indeed present, or whether mitigations are in place that would prevent exploitation.
The most effective way to avoid DOM-based JSON injection vulnerabilities is not to parse as JSON any string containing data that originated from an untrusted source. If the desired functionality of the application means that this behavior is unavoidable, then defenses must be implemented within the client-side code to prevent malicious data from modifying the JSON structure in inappropriate ways. This may involve strict validation of specific items to ensure they do not contain any characters that may interfere with the structure of the JSON when it is parsed.