Cache integrity is the trustworthiness of cached data: content stored for reuse must match the original, expected response and must not be altered by attackers, bugs, or corrupted processing. In a caching proxy, integrity means the cache serves the same approved object that was first stored, with headers and body still consistent with policy and application expectations.
This matters because caches sit between users and upstream services, so one bad write can affect many later requests. If an attacker can manipulate HTTP parsing, bypass a security check, or poison a cache entry, future clients may receive tampered content, incorrect redirects, or unsafe headers. Defenses include strict request validation, cache-key hygiene, careful handling of unusual HTTP syntax, and rapid patching of proxy software. Administrators also monitor for cache poisoning symptoms and clear suspect entries when integrity is in doubt.