#WAFv2

[govindhtech]

AWS WAFv2 For Hotlink Protection: Future Of Content Security

How to stop hotlinking with Amazon CloudFront, WAF, and referer checking.

AWS WAF Classic will be retired in September 2025. This update describes how to utilise the latest AWS WAF (WAFv2) to avoid hotlinking. Screenshots have been updated to reflect AWS WAF Management Console changes.

Hotlinking, also known as inline linking, is a kind of content leeching in which an unauthorised third-party website embeds links to resources referenced in a major website's HTML. Your website may be invoiced for third-party websites' content as they don't pay for hosting. Slow loading times, lost money, and legal issues may result.

Hotlinking may now be stopped using AWS WAF. AWS WAF, a web application firewall, integrates with Amazon CloudFront, a CDN, to protect your web apps from typical online vulnerabilities that can reduce application availability, security, and resource use.

Solution overview

There are several techniques to handle hotlinking. The Apache module mod_rewrite may verify the Referer header on your web server. You may then redirect the visitor to your site's home page or display a 403 Forbidden message.

If you utilise a CDN like CloudFront to speed up website delivery, web server Referer header validation is less useful. The CDN must validate additional requests for that content because they are unlikely to reach the origin web server, even if your web server verifies the headers (in this example, the referer). The CDN caches your stuff at the edge of its servers.

Figure 1: Cache request-response flow.Hit-and-miss cache encounters

Figure 1 shows the procedure:

A user client (1) requests from CloudFront edge point (2).

Edge locations try to return a cached file. This request is a cache hit if the cache replies.

The origin (3), which may be an Amazon S3 bucket, receives a request for a new copy of the object if there is a cache miss and the content is incorrect or not in the edge.

Cache hits prevent the origin from applying validation logic to the user's request since the edge server may fill the request without contacting the origin.

Two methods for solution implementation

This document provides two AWS WAF configurations to prevent hotlinking:

Transferring protected static assets (images or stylistic elements) to static.example.com ensures that you just need to check the Referer header.

Static files are in a directory on the same domain. This approach includes extending this example to check for an empty Referer header.

Your website structure and security needs will determine your strategy. The first approach lets you set up a Referer header check to guarantee that photo requests come from an allowlisted sub-domain, while the second way checks for an empty Referer header. The first technique prevents unaffiliated third-party sites from embedding image links, whereas the second allows users to share direct connections.

Terms

Key phrases from this post:

AWS WAFs use web ACLs tied to CloudFront distributions.

Each web ACL has one or more match criteria and rules.

Match conditions examine request headers or URIs for particular criteria using one or more filters.

The names of HTTP headers are not case-sensitive. Referer references the same HTTP header. However, HTTP headers are case-sensitive.

Requirements

A CloudFront distribution is needed to configure an AWS WAF web ACL. Configuring a CloudFront distribution with an S3 bucket origin is covered in Configure distributions.

Approach 1: Subdomain separation

This sample AWS WAF rule set comprises one rule, match condition, and filter. The match condition checks the Referer header for a given value. Traffic is allowed if the request meets rule conditions. If not, AWS WAF blocks traffic.

Due to the static files' subdomain (static.example.com) being accessible exclusively from example.com, you will restrict hotlinking for any file without a referral.

Approach 2: Domain-wide content with path filtering

The second technique filters by URL path and allows blank Referer headers. Create an AWS WAF web ACL with numerous rules and extra match criteria, which are filters. Instead than validating the Referer header once, the match condition validates it twice. First, check the request header. The URL-style Referer header is checked in the second validation.

Some people may prefer to share the photo URL directly. Accessing the picture directly in the browser can help avoid a negative user experience. This solution is better than the previous, which needed sub-domain picture requests.

You must also check the request route (/wp-content) for AWS WAF to protect multiple folders under a domain name.

In conclusion

AWS WAF, a web application firewall, monitors and manages HTTP(S) traffic to your protected web applications. Using the AWS WAF custom rule builder, you protected your website's Amazon S3 bucket content from hotlinking.

Preventing unauthorised third-party websites from connecting to your static content reduces bandwidth costs, user experience, and resource leeching. Two robust referrer check methods are described in this post. Following the least privilege approach, you may restrict AWS WAF rules to.jpg or.png image file extensions.

Referer checking prevents unaffiliated websites from utilising your bandwidth and backlinking to your images, but clever attacks can purposefully design a request to bypass it. Inconsistent referer header interpretation can also be caused by browser plugins, server-to-server queries that fake header data, or privacy-based web browsers. Recognise these anomalies and consider token authentication and signed URLs for private content protection.

Web browsers cannot detect changed Referer headers. Referer checking should be utilised with AWS WAF application protection rules, Bot Control, Fraud Control, and DDOS protection to secure online applications.

[ericvanderburg]

AWS WAF Classic vs WAFV2: Features and Migration Considerations

http://securitytc.com/TJsKVC

[takepara]

なるほどですね 2020年07月13日の記事一覧

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[ajo-mathew]

Azure Application Gateway Standard v2 and WAF v2 SKUs generally available

Application Gateway is Azure’s Application Delivery Controller as-a-service offering which provides customers with layer 7 load balancing, security and WAF functionality. Azure Application Gateway Standard v2 and WAF v2 SKUs are now generally available and fully supported with a 99.95 SLA. from Pocket https://azure.microsoft.com/en-in/updates/azure-application-gateway-standardv2-wafv2-skus-generally-available/ via IFTTT

[ericvanderburg]

AWS WAF Classic vs WAFV2: Features and Migration Considerations

http://securitytc.com/TJsH4C

[takepara]

なるほどですね

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