allowlists

An allowlist is a list of entities that are explicitly permitted to access a system, perform actions, or pass through a filter. By contrast, a blocklist (or blacklist) enumerates entities that are denied access. Allowlists are commonly used in network security, email handling, software distribution, and content moderation to enforce a default-deny stance.

The rationale is to minimize risk by permitting only trusted items while denying everything else. However, maintaining an accurate and up-to-date allowlist is essential, because stale entries can be misused, and performance or scalability concerns may arise as the list grows. Centralized management and regular reviews help mitigate these risks, while failures to update can create new vulnerabilities or operational bottlenecks.

Examples include network firewalls that allow traffic from whitelisted IP addresses, email systems that accept messages only from whitelisted domains or addresses, software update servers or app stores that distribute code only from whitelisted certificates, and content moderation systems that permit only approved sources or terms.

Terminology: the term whitelist has historical usage; many organizations prefer allowlist, permitlist, or allow-dlist to avoid connotations associated with the word white. Not all communities have adopted the alternative terminology.

Limitations: allowlists can become a maintenance burden and may hinder legitimate activity if not kept current. They are often most effective when combined with broader security strategies such as least privilege, continuous monitoring, and zero-trust architectures rather than as a sole control.

See also: blacklists, access control, zero-trust security, reputation-based filtering.