What is Via localStorage/sessionStorage – Sensitive Token Vulnerability?

LocalStorage and SessionStorage are HTML5 browser storage technologies. It enables JavaScript to save data in key-value pairs in web browsers. Most browsers offer up to 5MB of browser storage, allowing us to keep more data more effectively.

The key distinction between LocalStorage and SessionStorage is the sharing of data between browser windows and tabs.

Data from LocalStorage is shared between browser windows and tabs. Assume you have numerous tabs and windows open with the same program. If you change the LocalStorage in one of those tabs/windows, the modified LocalStorage data will be visible in all other tabs/windows.

SessionStorage data, on the other hand, is unaffected by the other tabs or windows. If two tabs are open and one of them updates the SessionStorage, the changes will not be mirrored in the other tabs/windows. Consider the following scenario: a user wishes to book two hotel rooms using two browser tabs. Because it necessitates distinct session data, SessionStorage is the best option for the hotel booking application.

XSS attacks inject malicious scripts into web applications, and LocalStorage and SessionStorage are both vulnerable to XSS attacks. XSS attacks may be used to extract data from storage objects and inject malicious scripts into the data.
For example, if we use third-party JavaScript libraries and they are injected with scripts that harvest storage objects, our storage data will no longer be safe. As a result, it is not advisable to preserve critical data as:

  • Username/Password
  • Credit card info
  • JWT tokens
  • API keys
  • Personal info
  • Session ids

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