What Is a Cache and Why Can It Be a Hidden Security Risk?

What Is a Cache?

A cache is a high-speed data storage layer that temporarily stores frequently accessed data. Its purpose is to improve performance by reducing the need to repeatedly retrieve data from the original source.

Caching data is a central part of modern computing and browsing. They can reduce latency and conserve bandwidth. But when misconfigured or not used with security in mind, they can exacerbate security and privacy risks.

Types of Caches

Different cache types serve distinct roles:

• Browser cache: Stores website assets such as images, scripts, and stylesheets on the hard drive to load pages faster on repeat visits
• CDN cache: Delivers cached content from geographically distributed locations for performance at scale

How Caches Create Security Risks

While caching is designed for efficiency, improper caching configurations and use can expose sensitive data or provide attackers with access vectors to inflict damage.

1. Sensitive Data Exposure

If cache rules are overly permissive, confidential content may be stored and served to unauthorized users For example, information can be exposed due to lack of “no-store” headers. These headers achieve what it sounds like: They instruct browsers to not store responses and can be applied for sensitive data use cases.

2. Exploiting Cached Credentials

Threat actors and cybercriminals widely deploy tools to steal cached credentials, exposing users who have credentials cached.

3. Cache Poisoning

Attackers can manipulate cache behavior to inject malicious content into stored caches and interrupt users’ workflows unexpectedly. They can, for example, redirect users to malicious sites and steal their data or deploy malware. One common example of this attack type is DNS cache poisoning.

4. Stale Data Risks

Caches that don’t expire can serve compromised or unauthorized data for extended periods. This can enable continued exposure to malicious sites if your cache hasn’t updated to a fixed version of the site.

5. Risky OPSEC

When individuals rely on public resources, such as those in libraries or at printing businesses, they may run the risk of leaving their sensitive cache information exposed to unintended viewers after use.

Securing Your Caching Infrastructure

Although not an exhaustive list, users can help defend against some attacks exploiting caches by:

• Changing default settings
• Barring password caching
• Setting up “no-store” headers
• Exercise best practices by clearing caches, when possible
• Consider excluding login pages, account settings, and payment forms from all caches

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