Whitelisting vs Blacklisting: What's the Difference?

Whitelisting and blacklisting are common methods used in cybersecurity to control access to computer systems, networks, and data. A whitelist defines approved entities that are permitted access, while a blacklist defines prohibited entities that are denied access.

By exploring whitelisting vs blacklisting, you'll gain an in-depth understanding of these fundamental access control techniques and be able to make informed decisions leveraging them as part of your cybersecurity strategy.

What is Whitelisting?

It is a list of approved users, systems, applications, IP addresses, email domains, websites, or other entities that are explicitly authorised to access a particular system, network, or resource. Whitelisting is based on a "default deny" approach to access control, meaning everything is denied access by default unless it is allowed by being included on the whitelist.

This makes whitelisting a very secure method to strictly limit access to only trusted entities that have been pre-approved.

For example, a whitelist could allow connections from specific internal IP address ranges to an application server, permit certain approved software programmes to run on company endpoints or authorise specific user accounts to access a database.

How Whitelisting Works

To implement whitelisting, you first need to define the list of approved, authorised entities based on your security policies and access requirements. This can include IP addresses, software applications, user accounts, web domains, etc.

Next, the compiled whitelist must be integrated into the systems and applications that need to enforce access control. This is done by configuring whitelisting policies, rules, and settings within the respective platforms.

What is Blacklisting?

Blacklisting is the opposite of whitelisting for access control. A blacklist is a list of users, IP addresses, applications, websites, or other entities that are explicitly prohibited from accessing a system, network, or resource.

Whereas whitelisting actively allows only approved access, blacklisting aims to simply block any requests from blacklisted sources while allowing all other access by default. It takes a "default allow" approach, permitting access unless something is specifically blacklisted.

How Blacklisting Works

Blacklists are created by enumerating known dangerous actors, unsafe websites, malicious apps, unsecured IP ranges, etc., that pose a security risk. These blacklists are integrated into security tools to automatically block matching traffic. A network firewall can deny any connection attempts from blacklisted IP addresses.

An email filter blocks messages from blacklisted domains. Endpoint antivirus prevents blacklisted applications or files from running. Blacklisting passively improves security by blocking known threats but allows unknown and unapproved access by default.

Blacklisting Vs Whitelisting: Comparing Pros and Cons

Advantages of Whitelisting:

• Very secure - Only trusted entities that are explicitly pre-approved in the whitelist will be allowed access, while everything else is denied by default.
• Blocks unknown threats and malware by default - The strict default-deny approach prevents access by new threats and malware that are not on the approved whitelist. Whitelisting assumes denial first before allowing.
• Simpler to manage than exhaustive blacklists - Whitelists tend to be smaller and more defined than blacklists that attempt to identify all possible threats. Approved access can be carefully managed versus trying to indefinitely keep up with new threats.
• Reduces risk of unauthorised access - By automatically denying any non-whitelisted traffic, the attack surface is greatly reduced, as most potential attacks are blocked by default. Only those entities on the whitelist can get through.

Disadvantages of Whitelisting:

• Can be difficult to fully implement across all systems - Getting whitelisting fully deployed on all infrastructure, endpoints, applications, cloud resources, etc., is challenging, requiring extensive planning and resources.
• Lacks flexibility - Any changes to the environment, like new users, devices, and apps, often require tedious whitelist updates. Day-to-day operations can be hampered.
• Can negatively impact user productivity if access is too restricted - Overly strict whitelists that don't accommodate normal business functions and workflows will limit users' ability to be productive. Excessively locked-down access causes frustration.
• Allowed entities still have access even if compromised - If a whitelisted entity like a user account becomes compromised, their continued presence on the whitelist grants the attacker access. Whitelists must be tightly managed.

Advantages of Blacklisting:

• Easy to initially implement by just blocking known bad actors - Blacklisting can provide some immediate protection by starting with and blocking currently known threats with minimal effort compared to comprehensive whitelisting.
• Allows access by default, so no impact on user productivity - Since blacklisting permits all traffic by default except for blocked items, user activities and workflows are generally unaffected, which avoids productivity issues.
• Flexible - No change needed for approved access sources - Blacklisting avoids constant updates that whitelisting requires when new legitimate sources need access since it allows traffic by default. Blacklists only need to be updated as new threats emerge.
• New threats can be quickly added to the blacklist - Blacklisting provides the flexibility to easily and rapidly add newly discovered threats and malicious actors to blocklists as needed to adapt to the evolving threat landscape.

Disadvantages of Blacklisting:

• Not inherently secure since it allows all access except blacklisted items - The default-allow approach means that blacklisting cannot provide robust, systemic security since anything unknown and unlisted is permitted by default.
• Blacklists require constant maintenance and updating - Effective blacklisting demands regular identification of new threats that must be continually added to blocklists. Otherwise, those threats will go undetected. Blacklists tend to grow very large over time.
• Not effective against zero-day or other unknown threats - Any threats too new to have been identified and blacklisted will bypass defences since blacklisting security depends wholly on its blocklist.
• Doesn't actively filter access to only what is approved - Because it focuses on blocking bad traffic rather than permitting good traffic, blacklisting allows access to unapproved sources by design.

Applications of Whitelisting Vs Blacklisting: Use Cases for Each Approach

When to Use Whitelisting:

• When you need to limit access to sensitive systems like financial databases or proprietary applications - Whitelisting provides strict access control to deny by default and only allows pre-approved entities like users and services to these high-value systems.
• When you have well-defined, known entities that need access, like authorised users and managed endpoints - Whitelisting works best when all approved people, devices, apps, etc., that require access are already known and can be enumerated in allowlists.
• When you want to default to denying rather than allowing unknown access - With whitelisting's deny-first approach, you can take a conservative stance by only allowing access in exceptions defined in whitelists vs. allowing broadly.
• When the priority is strict security over flexibility - If rock-solid security is paramount, whitelisting provides the strictest access controls.

When to Use Blacklisting:

• When flexibility is needed more than inherent security, like for general user computing - For less sensitive systems where users need general flexibility, blacklisting blocks known threats while allowing normal activity.
• When it's not practical to define the entirety of allowed access upfront - Unlike whitelisting, blacklisting doesn't demand you know and specify all legitimate access needs beforehand.
• When ease of implementation and use is a priority over restricting unknown access - Blacklisting can provide some initial protection quickly by just blocking already-identified threats with minimal disruption.
• When you simply need to block specific high-risk activities or known threats - Blacklisting excels at stopping known bad sites, IP addresses, applications, and more.

Whitelist Vs Blacklist: Examples of Appropriate Use Cases

Whitelisting:

• Allowing only specific pre-approved user accounts to access backend databases - Mitigates the risk of unauthorised data access.
• Permitting select IP address ranges to manage administrative interfaces - Limits network-based attacks on management systems.
• Whitelisting authorised applications for privileged operations - Prevents malware from elevated activity.

Blacklisting:

• Blocking access from IP ranges known to originate attacks - Stops attacks from known offender IPs.
• Blacklisting sites categorised as malware hosts by web filters - Limits employee exposure to harmful sites.
• Preventing employees from visiting prohibited websites - Enforces acceptable internet use policies.

The level of security versus flexibility needed will inform whether whitelisting or blacklisting is more applicable.

Implementation Considerations

Building Effective Allow lists/Block lists:

• Leverage internal policies, databases, and directories to comprehensively identify approved and prohibited entities based on what resources they should or should not have access to.
• Implement procedures to automatically update lists by integrating with identity systems, firewalls, proxies, SIEMs, and other security infrastructure to avoid manual efforts.
• Subscribe to external threat intelligence feeds to continually populate blacklists with newly identified threats, malicious domains, compromised IPs, etc., to ensure blocklists stay current.
• Carefully categorise entries into separate lists - users, IP addresses, applications, websites, domains, file hashes, software versions, etc. to allow for granular rulesets and policies.
• Make lists dynamic through automated procedures that can rapidly add or remove entries in response to new threats, changes in business needs, user onboarding/offboarding, etc.
• Audit whitelists and blacklists on an ongoing basis to systematically remove obsolete, invalid, or outdated entries and ensure ongoing accuracy.

Enforcing Whitelisting and Blacklisting Controls:

• Integrate allow lists and block lists into central directory services like Active Directory, LDAP, or identity management systems for consistent user access restrictions across applications and resources.
• Deploy network-based whitelists and blacklists via firewalls, proxies, secure web gateways, DNS filtering, and other security infrastructure at network boundaries to filter traffic based on IP reputation, geolocation, domains, URLs, and known threats.
• Implement host-based application whitelisting and blacklisting tools on servers and endpoints to strictly control what software programs and scripts can or cannot run based on allowlists and blocklists.
• Leverage cloud access security brokers (CASBs) and secure web gateways in SaaS environments to filter inbound web traffic against dynamic whitelists and blacklists.
• Enforce email blacklisting of dangerous domains, senders, and IPs at the email gateway before messages reach user inboxes.
• Centralise management of lists and enforcement policies through platforms like Microsoft Intune, CISCO ISE, and SIEMs for consistency across on-prem and cloud environments
• Supplement whitelisting and blacklisting controls with advanced tools like data loss prevention (DLP), rights management, user behaviour analytics, and machine learning techniques for further enforcement

Using Whitelisting and Blacklisting Together

Whitelisting and blacklisting can complement each other as part of a layered security strategy. Some ways they can be used together:

• Use blacklisting to block known malicious IP addresses and domains at the network perimeter via firewalls and secure web gateways while supplementing with whitelisting policies to limit outbound web traffic to only business-approved categories and sites.
• Leverage antivirus blacklisting on endpoints to detect and block known malware and viruses, paired with application whitelisting policies that only allow authorised programs to run in the first place.
• Implement identity management system blacklisting to deactivate banned users, combined with whitelisting of admin users to enable privileged access.
• Blacklist prohibited file types from being emailed based on attachment filtering, along with whitelisting of approved file types required for business.
• Block compromised user accounts via identity system blacklisting, as well as whitelisting authorised users for access to sensitive data or systems.

This layered approach combines the benefits of both techniques, comparing application whitelisting vs blacklisting, to establish tighter control over access to systems and data via multiple enforcement points. The more layers, the stronger the security posture becomes.

Conclusion

Blacklisting and whitelisting serve complementary purposes with tradeoffs. Whitelisting restricts access to only trusted entities for inherent security. Blacklisting blocks threats rapidly but allows unknown access.

Combining both techniques based on factors like system sensitivity, threats, and flexibility needs allows robust access controls. Evaluating blacklisting vs whitelisting tradeoffs enables crafting an optimal multi-layered strategy.

If security is a primary concern for you, then InstaSafe's layered security platform integrates with on-prem and cloud environments to enable granular access policies and automated threat response.

Moreover, InstaSafe's Multi-Factor Authentication prevents compromised credentials from granting access by requiring additional verification.

Frequently Asked Questions (FAQs)

1. Why is it called blacklist and whitelist?

Blacklists block access from prohibited entities, like a blacklist at a club. Whitelists allow access to approved entities, like a whitelist of VIP guests. The colour metaphor visually conveys if an entity is allowed (white) or denied (black).

2. What is the difference between whitelisting and blacklisting?

Whitelisting only allows access to approved entities and denies everything else by default. Blacklisting blocks known bad actors but permits access from unknown/unlisted entities by default.

3. What is an example of a blacklist?

A firewall blacklist that blocks incoming connection attempts from IP addresses known to be associated with malware, botnets, and other cyber threats is an example of a blacklist. This prevents attacks sourced from those dangerous IPs.