Always-on detections: eliminating the WAF “log versus block” trade-off

Traditional Web Application Firewalls typically require extensive, manual tuning of their rules before they can safely block malicious traffic. When a new application is deployed, security teams usually begin in a logging-only mode, sifting through logs to gradually assess which rules are safe for blocking mode. This process is designed to minimize false positives without affecting legitimate traffic. It’s manual, slow and error-prone.

Teams are forced into a trade-off: visibility in log mode, or protection in block mode. When a rule blocks a request, evaluation stops, and you lose visibility into how other signatures would have assessed it — valuable insight that could have helped you tune and strengthen your defenses.

Today, we’re solving this by introducing the next evolution of our managed rules: Attack Signature Detection.

When enabled, this detection inspects every request for malicious payloads and attaches rich detection metadata before any action is taken. You get complete visibility into every signature match, without sacrificing protection or performance. Onboarding becomes simple: traffic is analyzed, data accumulates, and you see exactly which signatures fire and why. You can then build precise mitigation policies based on past traffic, reducing the risk of false positives.

But we’re going one step further. We’re moving beyond request-only analysis to something far more powerful: Full-Transaction Detection.

Instead of looking at just the incoming request, this new detection correlates the entire HTTP transaction: request and response. By analyzing the full context, we dramatically reduce false positives compared to traditional request-only signature engines. More importantly, we uncover threats others miss, such as reflective SQL injection, subtle data exfiltration patterns, and dangerous misconfigurations that only reveal themselves in the response. 

Attack Signature Detection is available now in Early Access — sign up here to express interest. Full-Transaction Detection is under development; register here to be among the first to try it when it’s ready.

To provide full visibility on your traffic without slowing down the Internet, we had to change how we think about the request lifecycle. For customers who opt in, Attack Signature detection is now "always on." This means that as soon as traffic is proxied, all detection signatures are executed on every request, and the results are immediately visible in Security Analytics.

This "always-on" framework separates detection from mitigation. Detections run continuously, enriching analytics with metadata about triggered detections. This metadata is also added to the request as a new field, which customers can use to create custom policies within security rules.

^{Separating the detection of malicious payloads from the actions taken by security rules is the core of the always-on framework. This approach enhances the analytics experience and increases confidence when deploying new protections.}

Our existing Bot Score and Attack Score detections already follow this method. Attack Signature Detection provides the same coverage as our Managed Rules product but operates within this new framework.

Does this introduce additional latency to the request? No — this model is designed for efficiency. If a customer has not created a blocking rule based on a detection, the detection can be executed after the request has been sent to the origin server, ensuring that the detection itself introduces no additional latency to the traffic. Therefore, upon onboarding, the detection is enabled by default but does not impact traffic performance. When a rule is created, the detection is moved in-line with the request that might experience additional latency. The exact value depends on the traffic profile of the application. 

Compared to traditional, rule-based systems like the Cloudflare Managed Ruleset, the new detection offers a substantial advancement in web application security. This approach makes identifying malicious web payloads and deploying security rules significantly more user-friendly.

The Cloudflare Managed Ruleset is where our analyst team develops detections for common attack vectors, including SQL injection (SQLi), Cross Site Scripting (XSS), Remote Code Execution (RCE), and specific Common Vulnerabilities and Exposures (CVEs). Analysts typically release new rules weekly, with emergency releases deployed for high-profile vulnerabilities (such as the recent React2Shell release). Currently, over 700 managed rules are active in our Managed Ruleset. The new detections are also known as signature rules or simply signatures. They employ the same heuristics as Managed Rules but do not directly apply actions to traffic.

Each signature is uniquely identified by a Ref ID (similar to the Rule ID for the Managed Ruleset) and is tagged with both category and confidence. The category specifies the attack vectors the signature targets, while the confidence level indicates the likelihood of a false positive (a trigger on legitimate traffic). A rule can have only one confidence level but may have multiple categories. 

Category indicates what attack vector the rule refers to. The list of categories is long, but includes tags like SQLi, XSS, RCE or specific CVE with its number.

The confidence field is divided into two values, based on whether at least one signature from the corresponding group matches the traffic.

Confidence	Description
High	These signatures aim for high true positives and low false positives, typical for CVEs where payloads are identifiable without blocking legitimate traffic. They function like the Managed Ruleset’s default configuration.
Medium	These signatures, which are turned off by default in the Managed Ruleset, may cause false positives based on your traffic. Before blocking traffic matching these rules, assess their potential application impact.

The detection's analysis of a request populates three fields. These fields are accessible in Security Analytics and Edge Rules Engine, our core engine for Security Rules.

Field	Description	Where can be used
cf.waf.signature.request.confidence	Array. Aggregate the confidence scores associated with the matching signatures.	Analytics and Security Rules
cf.waf.signature.request.categories	Array. Aggregate the categories associated with the matching signatures.	Analytics and Security Rules
cf.waf.signature.request.ref	Array. Aggregates the Ref IDs of the matching signatures, up to 10.	Analytics and Security Rules

Security Analytics is at the core of the Cloudflare Application Security toolbox, providing a comprehensive, data-driven view of how signatures interact with your web traffic. It gives you the tools necessary to understand, measure, and optimize your web protection. Common use cases for combining Analytics with signatures include: design a security posture during the onboarding process, verify the most frequent attack attempts and create exceptions to handle false positives.

Once a new application is proxied through Cloudflare, Attack Signature Detection begins populating your dashboard with data. The initial step is to examine the aggregated matches, categorized by type and signature, to confirm that all potential attacks are being blocked. Analysts can do this by reviewing the top statistics for signatures, filtering the data to show whether requests were blocked, served from the cache, or permitted to reach the origin server. If any malicious requests are found to have reached the origin, analysts can quickly implement security rules. 

^{A breakdown of the total request volume matching attack signatures, categorized by their corresponding Category or Signature.}

Analytics provides insights into attack patterns, such as the most frequent CVEs based on traffic volume over time. This capability is designed for quickly identifying the dominant attack payloads targeting applications and verifying the efficacy of current protections against related CVEs. For example, analysts can monitor the attack frequency targeting a specific part of the application, like /api/, or confirm if known malicious payloads, such as React2Shell, are reaching a particular endpoint, such as the POST /_next/ Node.js path. Both the Analytics filters and the Attack Analysis tool can be used to perform this type of investigation.

^{A visualization within Security Analytics offers a time-series view of malicious payloads targeting the /api/ endpoint. This view groups the data to highlight the top five CVEs by volume.}

Analytics also help create exceptions and identifying false positives. An increase in matches for a specific rule, for instance, may suggest false positives rather than active exploitation. For example, an application that allows users to submit rich HTML content (such as a Content Management Systems or support ticketing system) may legitimately include markup that matches more generic XSS signatures. In these cases, a scoped exception can be applied to the affected endpoint, while keeping the protection enabled across the rest of the application. 

This approach is especially useful for evaluating medium-confidence signatures, which balance aggressive blocking with false-positive risk. The tool allows "what-if" scenarios against historical traffic to empirically determine production performance. This process helps determine if a medium-confidence signature is appropriate for the overall traffic profile, or if a high rate of false positives requires limiting its deployment to specific URLs or request types. 

Generally, signatures that have a very low match rate on historical traffic can be more safely deployed in block mode without significant disruption to legitimate traffic. To achieve this level of confidence, Security Analytics provides the tools for in-depth forensics investigations.

Beyond immediate detection, a crucial aspect of defense management is the ability to customize your security posture. The user interface offers a searchable catalog of all security signatures, allowing you to browse the full list and understand the specific threat each is designed to address. 

^{A searchable catalog of signatures is available, providing more detail on critical detections to help customers understand the threats and the remediation actions.}

After analyzing your data and establishing confidence in how the signatures performed against your past traffic, you can easily create custom rules to handle traffic based on the detections. For example, if you want to create a policy that blocks requests matching high confidence signatures you can create the following rule:

^{Creating a rule to block requests matching with high confidence signatures.}

This is equivalent to the Cloudflare Managed Ruleset default deployment.

If you want to block all requests matching at least one rule, you will add the Medium confidence tag. This is equivalent to enabling all rules of Cloudflare Managed Ruleset. Alternatively, you can configure multiple rules, applying a more stringent action (like "Block") for detections with High confidence and a less strict action (such as "Challenge") for those with Medium confidence.

^{By selecting both High and Medium confidence you can trigger a rule if any signature matches.}

To create a rule blocking a specific CVE or attack vector, you will use Categories. The rule builder allows you to combine attack vector category tags with all existing HTTP request data. This enables you to create granular rules (or exceptions) and tailor your security posture to different parts of your application. 

^{Customers can create rules to block (or allow) requests matching specific CVEs or attack categories.}

To create rules based on a specific Signature, you can use Ref ID. You can find the right Ref ID within the rule builder by exploring the available Attack Signature rules. This is especially useful if you want to create exceptions to manage false positives.

^{Customers can browse signature rules directly from the rule builder.}

All customers continue to have access to our classic Managed Ruleset. When Attack Signature Detection is broadly available, customers will be able to choose the deployment model that best suits their needs, whether that is Attack Signature Detection or Managed Rules. Our analyst teams ensure that new detections are released simultaneously across both the Managed Ruleset and Attack Signature Detection.

Traditional web attack detection primarily focuses on the "ask": the HTTP request. However, the request only tells half the story. To know if an attack actually succeeded, you have to look at the "answer": the HTTP response.

By combining request and response metadata into a single detection event, we can dramatically reduce false positives and identify successful exploits that request-only systems miss.

For example, consider a request containing a common SQL injection string in a query parameter.

GET /user?id=1' UNION SELECT username, password FROM users--

A traditional WAF will see the UNION SELECT pattern and block it. However, if the application isn't actually vulnerable, this might be a false positive — for instance a security researcher testing their own site.

With Full-Transaction Detection, the system notes the SQLi signature in the request but waits for the response. If the origin responds with a 500 Internal Server Error or a standard 404, the confidence of a "successful exploit" is low. If the origin responds with a 200 OK and a body containing a string that matches a "sensitive data" signature (like a list of usernames), the system flags a Successful Exploit Confirmation.

To start, we are rolling out a few detection categories and plan to expand this list over time. Here are the three areas we are currently focused on, and some of the flags you’ll see:

• Exploit attempts. The detection provides web attack detections by inspecting the entire HTTP request-to-response cycle. It focuses on three key areas: identifying input exploitation like XSS and SQLi via malicious signatures, stopping automated abuse such as vulnerability probing, and confirming successful exploits by correlating suspicious requests with unusual server responses.

• Data exposure and exfiltration signals. This framework also allows us to catch data exfiltration that looks like legitimate traffic on the way in. A request for /api/v1/export is a standard administrative action. But if that specific request triggers a response containing 5,000 credit card numbers (for example identified via Luhn algorithm signatures), the transaction is flagged as Data Exposure. 

• Misconfigurations. Exposed admin interfaces are often attack vectors. Traditional security checks miss this misconfiguration because the traffic itself looks valid (real endpoints or admin pages). The issue isn't the traffic but its public accessibility. We prioritize detection based on common real-world misconfigurations seen in customer data, such as public unauthenticated Elasticsearch clusters, Internet reachable admin panels, and exposed Apache sensitive endpoints.

The detection, much like Attack Signatures, will store the results in two specific fields. These fields are accessible in our dashboard and logged within Security Analytics.

Field	Description	Where can be used
cf.waf.signature.response.categories	Array. Aggregate the categories associated with the matching signatures.	Security Analytics
cf.waf.signature.response.ref	Array. Aggregates the Ref IDs of the matching signatures, up to 10.	Security Analytics

Initially, we are focused on offering visibility into matching requests via analytics. By surfacing events on potential exploits, we provide customers information that can be used for incident response through targeted remediations across their infrastructure and software stack. Our future plans include extending Security Rules to the response phase, which will empower customers to block responses based on these detections by allowing policy creation.

^{A diagram illustrating the execution locations and corresponding populated fields for both Attack Signature Detection and Full-Transaction Detection.}

Attack Signature detection is in Early Access while Full-Transaction Detection is under development. Sign up here to get access to Attack Signature, and here to express interest for Full-Transaction. We’ll gather feedback in the coming months as we prepare these features for General Availability.