In the ever-evolving landscape of cybersecurity, administrators and professionals often face a pivotal decision: Should they rely on pre-compiled, fixed IP blocklists for protection, or should they adopt more dynamic, real-time monitoring and response solutions? While both approaches offer their own sets of advantages, it's critical to understand their respective limitations, especially in today's fast-paced and complex attack environment.
This article delves deep into the two methodologies, exploring the pros and cons of using fixed IP block lists versus real-time monitoring, based on both theoretical frameworks and real-world experience.
Fixed IP block lists are databases of known malicious or suspicious IP addresses maintained by cybersecurity companies or collaborative communities. These lists are designed to block connections from IPs that have been identified as threats, such as those associated with botnets, phishing attacks, or distributed denial-of-service (DDoS) campaigns. Many network security tools (firewalls, intrusion detection systems, and web application firewalls) can implement these lists as a first line of defense.
Real-time monitoring involves tracking incoming and outgoing network traffic to identify and respond to suspicious activity as it happens. Tools like Fail2Ban, Snort, or other Intrusion Detection and Prevention Systems (IDS/IPS) detect patterns or signatures indicating an attack, allowing administrators to take immediate action.
Many organizations adopt a hybrid approach, combining blocklists with real-time monitoring. This strategy offers the quick protection of blocklists while allowing the flexibility and adaptability of real-time defenses.
In practice, relying solely on blocklists has proven problematic for many administrators. For example, using a fixed IP blocklist was initially effective in blocking 63% of malicious IPs. However, that effectiveness soon dropped to only 7%, leaving the majority of traffic unblocked.
Real-time monitoring, on the other hand, blocked 93% of attack attempts,
particularly those from new and emerging threats. While tools like Snort can
provide additional layers of security, their aggressive rules can also block
legitimate traffic, such as important files like robots.txt.
Snort’s heavy-handed blocking, along with similar issues in Cloudflare
and UFW, have led to frustration among admins, showing that these tools are
not always the “drop-in fix-all” solutions they appear to be.
Another issue with fixed IP blocklists is that they are only updated semi-regularly. Even just a few hours’ delay in updates—let alone if the list only updates once a day or longer—can leave the server exposed to malicious traffic for extended periods while waiting for the new IPs to be added. Worse yet, these updates may not include the specific offending IPs in your case, meaning the server remains vulnerable. This delay in updates demonstrates a major limitation of relying on third-party blocklists.
A crucial aspect often overlooked in the debate over fixed IP block lists is the issue of trust. When using third-party block lists, you're relying on external organizations to correctly maintain and update their databases. While this may seem efficient, it comes with significant risks, particularly when it comes to blocking legitimate traffic.
One common scenario is when entire subnets are blocked, rather than individual IPs. Many blocklists take a broad approach by blocking full IP ranges, which can cause unintended collateral damage. For instance, entire subnets from countries like China are often blocked due to suspicious activity originating from a few malicious users. While this may prevent some attacks, it also inadvertently blocks legitimate traffic, such as emails or other critical services from the same region.
These broad blocks can severely impact users and businesses with global reach. Legitimate users trying to access your services may be locked out, simply because they happen to share an IP range with a bad actor. This is especially problematic when it comes to important communications like emails, where blocking a full subnet can result in critical messages being undelivered.
From personal experience, I have faced numerous issues with IP blocklists that block entire subnets, particularly in China. This broad approach has locked out genuine traffic and created more problems than it solved. The issue is compounded by the fact that third-party blocklists often fail to remove these blocks in a timely manner or at all.
Furthermore, services like Cloudflare or Microsoft, while widely trusted, are also known for overly aggressive blocking policies. Cloudflare, for example, has blocked legitimate traffic, including services essential to my own operations. Despite its widespread use, the inability to reliably prevent legitimate traffic from being blocked, coupled with the difficulty of getting removed from these blocklists, has led to ongoing frustration. Even when you manage to get removed, there's a high chance of being blocked again, creating a cycle of recurring issues. Microsoft, while they offer removal request pages, often provides only short-lived relief. Despite Microsoft being unable to verify why certain IPs are blocked in the first place, they continue doing so. This leads to the frustrating process of submitting weekly or even daily requests to remove mistakenly blocked IPs, which is ineffective as a long-term solution.
This trust issue is a major reason why I no longer use tham as there's a high chance of being blocked again, creating a cycle of recurring issues. This is a major reason why I no longer rely on such blocklists. While they may offer a quick fix, they come with significant risks of over-blocking and can cause long-term damage to user experience and business operations. Relying on third-party services or blocklists without active monitoring and false-positive management has caused so many issues that I no longer trust them in any way, shape, or form.
There is often concern as to where IP block lists get their data from. Since many of these lists are managed by corporate entities, it seems likely that they focus primarily on monitoring attacks from the worst and most notorious IP addresses. While such an approach can be effective in protecting smaller hobby servers, in my experience, even a few hundred IP addresses that are not monitored or blocked by corporate lists are enough to wreak havoc on hobby servers.
Often, large corporations are not particularly concerned with smaller-scale attacks that do not affect their infrastructure, making it understandable that they may not invest resources in addressing such threats. Unfortunately, this means that IP block lists are even less likely to be proactive in protecting small servers if the larger corporations are not actively monitoring these smaller, yet potentially harmful, attacks. This can leave hobbyists and small server operators vulnerable to threats that would otherwise be ignored by mainstream block lists.
In the realm of cybersecurity, IP blacklists serve as a fundamental tool for blocking malicious traffic and protecting systems from unauthorized access. However, maintaining a publicly accessible blacklist can introduce vulnerabilities and even undermine the very security it aims to provide. While a publicly accessible blacklist might seem beneficial for transparency or community-based security efforts, it can be a double-edged sword, particularly when dealing with sophisticated bad actors who adapt to avoid detection.
One of the primary issues with a public blacklist is that it can be easily scraped by malicious entities. Cybercriminals, bots, and other bad actors often look for ways to evade detection, and a publicly accessible list gives them direct access to the IP addresses that are blocked. By examining these lists, attackers can modify their methods, switching to unlisted IPs or deploying other tactics to bypass the blacklist. Essentially, a public list becomes a roadmap that allows bad actors to avoid specific defenses, making it easier for them to exploit vulnerabilities in the network.
Bad actors who scrape public blacklists can quickly adapt their strategies. For example, if an attacker’s IP is blocked, they can simply switch to a new IP address that isn’t on the list, allowing them to continue their activities undetected. In a more advanced approach, malicious entities can analyze patterns in public blacklists to determine how certain organizations or services respond to threats. This insight enables attackers to modify their approach, targeting weaker points or shifting tactics to evade detection and stay ahead of countermeasures.
Maintaining a private, internal blacklist provides a significant advantage in cybersecurity. By keeping the list confidential, organizations reduce the risk of bad actors finding and exploiting their blocking strategies. This privacy allows for more dynamic and proactive management of potential threats, as IP addresses can be blocked, updated, and removed without external visibility. Without easy access to the list, attackers are left guessing which IPs might be blocked, making it more challenging for them to circumvent the system.
While transparency is often valuable, especially in collaborative cybersecurity efforts, the risks associated with a public blacklist usually outweigh the benefits. Security professionals can still collaborate on threat intelligence and other defensive strategies without exposing active blacklists. Many organizations use trusted third-party sources for threat intelligence or contribute to shared databases, all while maintaining their private lists. This balance enables a more secure, adaptable, and responsive approach to cybersecurity.
Ultimately, the decision to keep a blacklist private is an essential part of a robust cybersecurity strategy. Publicly accessible blacklists can inadvertently aid malicious actors by giving them a blueprint to bypass defenses. By maintaining private blacklists, organizations can enhance their security posture, effectively limiting attackers’ ability to evade detection and better protecting their systems against evolving threats.
When defending a website or network from malicious traffic, many administrators turn to IP blocklists, hoping to proactively block attackers. FireHOL, for example, offers access to over 300 IP blocklists. While this seems comprehensive, our testing has shown that relying solely on these blocklists can be far less effective than anticipated.
In our assessment, we used FireHOL's IP ban lists, comparing our own IP ban list against all 322 blocklists. The results were underwhelming: only 51% of the IPs we detected in real-time matched entries on these lists. This means 49% of the IPs flagged as threats weren’t present in the blocklists, even with the extensive resources FireHOL provides.
FireHOL itself estimates a match rate of around 50% to 80%, but our findings suggest that even at the upper end, these lists can only partially address real-time threats. Achieving the 51% match rate required using all 322 blocklists, which demands significant bandwidth and CPU power. Additionally, this vast number of lists increases the risk of false positives, potentially blocking legitimate traffic and making management even more challenging.
Depending on the specific blocklists used, results can vary significantly. Some lists are highly specialized and may not include general threat IPs, rendering them almost entirely ineffective for broad protection. Using a smaller subset of lists would likely result in even fewer matches.
In conclusion, while IP blocklists can offer some value, they are limited in their capacity to handle real-time threats independently. For comprehensive security, blocklists should be used alongside other monitoring and detection systems. This layered approach can provide more effective protection against evolving threats and ensure that networks remain as secure as possible. However, because of the general ineffectiveness of these lists, while they certainly can help with bad traffic, they’re ultimately nothing more than a Band-Aid solution or a short-term quick fix for a much deeper set of problems. The administrative nightmare of tracking false positives across 322 lists, potentially needing to remove several IPs daily due to false matches, quickly turns into an overwhelming management burden.
These results are from our test of over 6,300 currently blocked IPs compared to all the FireHOL lists:
Note that lists with zero matches have been omitted from the above results.
The standout performer in our tests was blocklist.de, achieving an impressive 40% match rate with our own list. In contrast, the majority of other lists had a match rate of no more than 7%. At the time of writing in October 2024, we attempted to join blocklist.de to contribute our own list, but unfortunately, we were unable to complete the registration process and could not log in to the site.
Blocklist.de operates by collecting reports of suspicious IP activity from users and contributing sources, aggregating these into lists of IP addresses flagged for malicious behavior, such as SSH attacks, email abuse, and web attacks. These lists can be integrated with Fail2Ban, allowing Fail2Ban to automatically block IPs identified by blocklist.de based on specific criteria. This setup provides an additional layer of protection by preventing known bad actors from accessing a server in the first place, enhancing the effectiveness of real-time blocking solutions. Later we found abuseipdb.com offering a similar service and can easily intergrate into fail2ban etc.
Shortly after compiling the above list (11th October 2024), our server was subjected to a heavy attack from hundreds of IP addresses associated with ClearDocks LLC ISP. We downloaded all the available block lists, waited 24 hours, and then compared our detected DDoS attack IPs against these lists. We discovered that none of the attacking IPs were present in any of the block lists. This essentially means our server would have remained completely unprotected for at least 24 hours during this new attack. This attack went on for the next several days before they finally subsided.
The following is a complete IP list with resolved host names, highlighting the number of IP addresses targeting our server. This list is not actively maintained or updated and is provided solely for historical reference. It is worth noting that DDoS-style attacks have originated from hundreds of IP addresses associated with CLEARDOCKS LLC.
Additionally, it is ironic that Cloudflare, a company known for providing network services, cloud cybersecurity, and DDoS mitigation, has IP addresses that have been identified performing SQL injection attacks on our server!
While fixed IP block lists can offer a quick and seemingly straightforward solution to many common cyber threats, their static nature and reliance on external sources present significant limitations. From outdated information to the risk of over-blocking legitimate traffic, sometimes even entire subnets, these lists provide only a partial defense against the dynamic, evolving threat landscape. Moreover, shared IP addresses in cloud or hosting environments mean that blocking a single IP could inadvertently affect numerous legitimate users, leading to a high incidence of collateral damage.
Real-time monitoring solutions, such as Fail2Ban, may require more effort to set up and maintain, but they offer a level of customization and adaptability that third-party lists simply can't match. These systems allow administrators to respond to specific attack patterns in real-time and fine-tune their defenses based on what's happening in their environment, not just what a list tells them to block. This proactive approach is particularly effective against threats from attackers who frequently change IPs or use dynamic IP ranges, which traditional block lists often struggle to keep up with.
Importantly, it's not enough to blindly rely on third-party services or block lists without monitoring. These services can, and often do, lead to unforeseen problems, including blocking legitimate traffic. Trying to resolve these issues with third parties can be time-consuming and frustrating, taking valuable time away from more productive activities like refining your own rules and lists to ensure they fit your specific needs. Additionally, delisting requests may take considerable time to process, during which essential services can remain inaccessible.
Of course, inexperienced admins often turn to services like Cloudflare for a quick solution, and while these tools have their place, they can cause more issues than they solve if not monitored correctly. Misconfigurations or overly aggressive blocking policies can result in business disruptions that far outweigh the initial convenience. Additionally, users frequently report challenges with Cloudflare's block lists due to the difficulty of removing IPs and the likelihood of being re-listed, making these solutions more cumbersome than helpful for some.
Frustrations with Cloudflare and Third-Party Block Lists: From experience, services like Cloudflare can block legitimate traffic, including your own services. This issue is compounded by the difficulty in getting removed from block lists and the high likelihood of being re-listed, making third-party solutions more of a hassle than a help. This aligns with broader experiences from others who have also encountered difficulties getting their IPs or services removed from Cloudflare's block lists or resolving conflicts with these services.
In summary, while IP block lists and services like Cloudflare can provide a quick and easy layer of defense, they are far from perfect. You still need to actively monitor their impact on your traffic, as false positives and over-blocking can cause more harm than good. This reinforces the argument that relying on real-time monitoring and custom rules, such as Fail2Ban, while more time-consuming, offers greater control and adaptability to your specific environment. Additionally, questionable update and removal times for IPs in block lists mean that even a few hours' delay in updating the lists is enough for your server to become compromised or fall victim to DDoS attacks and other threats.
In the end, no solution is truly "set it and forget it." Whether you choose block lists, real-time monitoring, or a combination of both, the key is ongoing vigilance and adaptability. For long-term success in cybersecurity, you need to stay engaged with the threats your system faces, continually refine your defenses, and ensure that quick fixes don't turn into long-term liabilities.