[Security] Multiple Unsafe JSON.parseExn Usages

[muditbhutani]

Summary

JSON.parseExn throws an exception on invalid JSON input. Several call sites use it on untrusted data (sessionStorage, DOM events, API error messages) without adequate error handling, which can cause application crashes or expose unexpected behavior.

Affected Locations

#	File	Line	Input Source	Error Handling	Risk
1	src/context/FilterContext.res	177	sessionStorage	None	HIGH
2	src/components/HandlingEvents.res	12	postMessage DOM event	try/catch present	MEDIUM
3	src/screens/Developer/PaymentSettingsRevamped/AcquirerConfigSettingsRevamp/AcquirerConfigSettingsRevamp.res	62	API error message	outer try/catch only	MEDIUM
4	src/screens/Developer/PaymentSettings/AcquirerConfigSettings/AcquirerConfigSettings.res	61	API error message	outer try/catch only	MEDIUM
5	src/screens/PaymentLinkThemeConfigurator/PaymentLinkThemeConfiguratorTool.res	61	WASM return value	outer try/catch only	MEDIUM

src/utils/LogicUtils.res line 36 (safeParseOpt) is a safe wrapper and is not an issue.

Highest-Risk Case — FilterContext.res Line 177

switch sessionStorage.getItem(`${index}-list`)->Nullable.toOption {
| Some(value) =>
  switch value->JSON.parseExn->JSON.Decode.array {   // <-- no try/catch
  | Some(arr) => ...
  | None => ()
  }
| None => ()
}

sessionStorage can be written by any same-origin JavaScript. If the stored value is malformed JSON, JSON.parseExn throws an unhandled exception that crashes the filter context, breaking the dashboard UI.

Impact

• FilterContext crash: corrupted or attacker-manipulated sessionStorage can force an unhandled exception, making filters non-functional
• Cascading failures: other call sites with only outer-scope try/catch may silently swallow errors and leave the UI in an inconsistent state

Severity: MEDIUM–HIGH

Recommended Fix

1. FilterContext.res line 177 — wrap with an immediate try/catch or use LogicUtils.safeParseOpt instead of JSON.parseExn
2. All other sites — replace JSON.parseExn on untrusted sources with LogicUtils.safeParseOpt and handle the None case explicitly
3. Establish a lint rule or code review checklist item: JSON.parseExn must never be called without a surrounding try/catch or a safe-parse wrapper when the source is external (API, storage, events)

References

• ReScript JSON docs: https://rescript-lang.org/docs/manual/latest/api/js/json

[gitanjli525]

Not a security issue, but handling these make the code more robust.