Thinking Outside the Box: Rewriting Web Pages with F5 Distributed Cloud (XC)
This article demonstrates how to dynamically rewrite web page content, such as updating links or replacing text, by using native features in F5 Distributed Cloud (XC). It provides a creative workaround that leverages JavaScript injection to modify pages on the fly, avoiding the need for a separate proxy like NGINX or BIG-IP.Simplifying Application Health Monitoring with F5 BIG-IP
A simple agreement between BIG-IP administrators and application owners can foster smooth collaboration between teams. Application owners define their own simple or complex health monitors and agree to expose a conventional /health endpoint. When a /health endpoint responds with an HTTP 200 request, BIG-IP assumes the application is healthy based on the application owners' own criteria. The Challenge of Health Monitoring in Modern Environments F5 BIG-IP administrators in Network Operations (NetOps) teams often work with application teams because the BIG-IP acts as a full proxy, providing services like: TLS termination Load balancing Health monitoring Health checks are crucial for effective load balancing. The BIG-IP uses them to determine where to send traffic among back-end application servers. However, health monitoring frequently causes friction between teams. Problems with the Traditional Approach Traditionally, BIG-IP administrators create and maintain health monitors ranging from simple ICMP pings to complex monitors that: Simulate user transactions Verify HTTP response codes Validate payload contents Track application dependencies This leads to several issues: Knowledge Gap: NetOps may not fully grasp each application's intricacies. Change Management Overhead: Application updates require retesting monitors, causing delays. Production Risk: Monitors can break after application changes, incorrectly marking services as up/down. Team Friction: Troubleshooting failed health checks involves tedious back-and-forth between teams. A Cloud-Native Solution The cloud-native and microservices communities have patterns that elegantly solve these problems. One widely used pattern is the [health endpoint], which adapts well to BIG-IP environments. The /health Endpoint Convention Cloud-native applications commonly expose dedicated health endpoints like /health, /healthy, or /ready. These return standard status codes reflecting the application's state. The /health endpoint provides a clear contract between NetOps and application teams for BIG-IP integration. Implementing the Contract This approach establishes a simple agreement: Application Team Responsibilities: Implement /health to return HTTP 200 when the application is ready for traffic Define "healthy" based on application needs (database connectivity, dependencies, etc.) Maintain the health check logic as the application changes BIG-IP Team Responsibilities: Configure an HTTP monitor targeting the /health endpoint Treat 200 as "healthy", anything else as "unhealthy" Benefits of This Approach Aligned Expertise: Application teams define health based on their knowledge. Less Friction: BIG-IP configuration stays stable as applications evolve. Better Reliability: Health checks reflect true application health, including dependencies. Easier Troubleshooting: The /health endpoint can return detailed diagnostic info, but this is ignored by the BIG-IP and used strictly for troubleshooting. Implementation Examples F5 BIG-IP Health Monitor Configuration ltm monitor http /Common/app-health-monitor { defaults-from /Common/http destination *:* interval 5 recv 200 recv-disable none send "GET /health HTTP/1.1\r\nHost: example.com\r\nConnection: close\r\n\r\n" time-until-up 0 timeout 16 } Node.js Health Endpoint Implementation const express = require('express'); const app = express(); const port = 3000; app.get('/', (req, res) => { res.send('Application is running'); }); app.get('/health', async (req, res) => { try { const dbStatus = await checkDatabaseConnection(); const serviceStatus = await checkDependentServices(); if (dbStatus && serviceStatus) { return res.status(200).json({ status: 'healthy', database: 'connected', services: 'available', timestamp: new Date().toISOString() }); } res.status(503).json({ status: 'unhealthy', database: dbStatus ? 'connected' : 'disconnected', services: serviceStatus ? 'available' : 'unavailable', timestamp: new Date().toISOString() }); } catch (error) { res.status(500).json({ status: 'error', message: error.message, timestamp: new Date().toISOString() }); } }); async function checkDatabaseConnection() { // Check real database connection return true; } async function checkDependentServices() { // Check required service connections return true; } app.listen(port, () => { console.log(`Application listening at http://localhost:${port}`); }); Adopting this health check pattern can greatly reduce friction between NetOps and application teams while improving reliability. The simple contract of HTTP 200 for healthy provides the needed integration while letting each team focus on their expertise. For apps that can't implement a custom /health endpoint, BIG-IP admins can still use traditional ICMP or TCP port monitoring. However, these basic checks can't accurately reflect an app's true health and complex dependencies. This approach fosters collaboration and leverages the specialized knowledge of both network and application teams. The result is more reliable services and smoother operations.NGINX Plus Request body Rate Limit with the NJS module and javascript
The nginx njs module allows javascript to process the code or as they call it on the backend nodejs. The module is dynamic for Nginx Plus https://docs.nginx.com/nginx/admin-guide/dynamic-modules/dynamic-modules/ while for the community nginx it needs to be compiled. The code and nginx configuration are also present at: https://github.com/Nikoolayy1/nginx_njs_request_body_limit/tree/main I have used the example rate limiter from https://github.com/nginx/njs-examples and https://clouddocs.f5.com/training/community/nginx/html/class3/class3.html and modified rate limit example to be based on the request body. It works as expected. The "r.internalRedirect('@app-backend');" internal redirect is needed as nginx by default does not populate or save the request body and this is why the request needs to pass 2 times in nginx proxy for the body variable to be properly populated! The nginx plus rootless container is a great option for F5 XC RE where root containers are not accepted and for Nginx on XC RE I have made another article at F5 XC vk8s open source nginx deployment on RE | DevCentral NJS "main" file code: const defaultResponse = "0"; const user = 'username'; const pass = 'username'; function ratelimit(r) { switch (r.method) { case 'POST': var body = r.requestText; r.log(`body: ${body}`); if (r.headersIn['Content-Type'] != 'application/x-www-form-urlencoded' || !body.length) { r.internalRedirect('@app-backend'); return; } var result_user = body.includes(user); var result_pass = body.includes(pass); if (!result_user) { r.internalRedirect('@app-backend'); return; } const zone = r.variables['rl_zone_name']; const kv = zone && ngx.shared && ngx.shared[zone]; if (!kv) { r.log(`ratelimit: ${zone} js_shared_dict_zone not found`); r.internalRedirect('@app-backend'); return; } const key = r.variables['rl_key'] || r.variables['remote_addr']; const window = Number(r.variables['rl_windows_ms']) || 60000; const limit = Number(r.variables['rl_limit']) || 10; const now = Date.now(); let requestData = kv.get(key); if (requestData === undefined || requestData.length === 0) { requestData = { timestamp: now, count: 1 } kv.set(key, JSON.stringify(requestData)); r.internalRedirect('@app-backend'); return; } try { requestData = JSON.parse(requestData); } catch (e) { requestData = { timestamp: now, count: 1 } kv.set(key, JSON.stringify(requestData)); r.internalRedirect('@app-backend'); return; } if (!requestData) { requestData = { timestamp: now, count: 1 } kv.set(key, JSON.stringify(requestData)); r.internalRedirect('@app-backend'); return; } if (now - requestData.timestamp >= window) { requestData.timestamp = now; requestData.count = 1; } else { requestData.count++; } const elapsed = now - requestData.timestamp; r.log(`limit: ${limit} window: ${window} elapsed: ${elapsed} count: ${requestData.count} timestamp: ${requestData.timestamp}`) let retryAfter = 0; if (requestData.count > limit) { retryAfter = 1; } kv.set(key, JSON.stringify(requestData)); if (retryAfter) { r.return(401, "Unauthorized\n"); return; } default: r.internalRedirect('@app-backend'); return; } } export default {sub, header, ratelimit, parseRequestBody, log}; Nginx nginx.conf file: server { listen 80 default_server; server_name localhost; access_log /var/log/nginx/host.access.log main; js_var $rl_zone_name kv; # shared dict zone name; requred variable js_var $rl_windows_ms 30000; # optional window in miliseconds; default 1 minute window if not set js_var $rl_limit 3; # optional limit for the window; default 10 requests if not set js_var $rl_key $remote_addr; # rate limit key; default remote_addr if not set js_set $rl_result main.ratelimit; # call ratelimit function that returns retry-after value if limit is exceeded root /var/www/html; index index.html; include /etc/nginx/mime.types; error_log /var/log/nginx/host.error_log debug; if ($target) { return 401; } location / { js_content main.ratelimit; } location @app-backend { internal; proxy_pass http://backend; } location /backend { internal; proxy_set_header Host httpforever.com; proxy_pass http://backend/; } Summary: There is another example how to populate the internal request body variable using that is needed by the njs module using the " mirror " option, shown at https://www.f5.com/company/blog/nginx/deploying-nginx-plus-as-an-api-gateway-part-2-protecting-backend-services but it did not work for me, so I used the " internal " option with "r.internalRedirect(uri)" https://nginx.org/en/docs/njs/reference.html Nginx njs feature r.subrequest can be used to populate response headers and body but mainly it is for logging and not for rate limiting and I think making a real http subrequest using javascript is not optimal and will not scale well, so I will not recommend this option as rate limiters are best left to be request based. Also I saw strange bug that the subrequest changes the content type header of the response and I had use "js_header_filter" to again change the response header.Nginx App Protect has the BD process from F5 BIG-IP AWAF/ASM that has DOS protections that can monitor the Server's response latency dynamically and make auto thresholds!Javascript injecting systems effect on web application end users - a scenario review
Hello! ArvinF is back to share a scenario review where Javascript-injecting systems affected web application end users - web and mobile application. Problem Users are failing to login to a web application protected by BIG-IP ASM/Adv WAF and Shape Security Defense. The site owner notes that the authentication was failing for an unknown reason. There were ASM Support ID noted and an error informing to enable Javascript. Please enable JavaScript to view the page’s content. Your support ID is: xxxxxxxxxxxx Troubleshooting To understand the cause of the authentication failure, we gathered HTTP traffic through a HTTP sniffer. We used httpwatch and gathered HAR (HTTP Archive) files. The site was protected with both on-premise BIG-IP ASM/Adv WAF bot defense and back then, Shape Security Defense (now F5 Distributed Cloud Bot Defense). After the review of the HAR file in httpwatch, the following were noted: ASM blocks a request in a URL related to authentication with a Support ID in the response. There was also javascript code included and it references https[:]//s[.]go-mpulse[.]net/boomerang/. The authentication attempt failed with an error in the HTTP response: ...unable to process your request. Please try again later... BIG-IP ASM/Adv WAF related HTTP cookies from its various features such as Bot Defense Client Side challenges as TSPD_101* cookie was present and other TS cookies, which could also come from Bot defense and DoS profile and security policy configurations. There were also HTTP cookies coming from BIG-IP AVR - f5_cspm cookie was present. Application Visibility and Reporting (AVR) module provides detailed charts and graphs to give you more insight into the performance of web applications, with detailed views on HTTP and TCP stats, as well as system performance (CPU, memory, etc.). https://clouddocs.f5.com/training/community/analytics/html/index.html https://clouddocs.f5.com/api/irules/AVR_CSPM_INJECTION.html Seeing the javascript code referencing "/boomerang/" included in the ASM blocking response was interesting. Reviewing the HAR file, there were several instances of this "/boomerang/". This finding was inquired with the site owner and they noted that there is another system that is in the path between the end users and their web application - a CDN. The traffic flow is as follows: End user web browser / mobile application >>> CDN >>> FW >>> BIG-IP >>> web application On the BIG-IP Virtual Server that fronts the web application, F5 AVR profile, ASM/Adv WAF Bot defense, and security policy and Shape Security defense iRule are configured. From the F5 side, these were the products with features that may insert Javascript in the client-side response. As part of troubleshooting, to isolate the feature that might be causing the failing authentication for the web application, the bot defense profile was removed from the site's Virtual Server and the Shape Security iRule and AVR profile were left untouched. Site owner noted that the authentication works after this change. Shape Security Defense was implemented using an iRule to protect specific URIs. When the iRule was removed from the Virtual Server and the Bot defense and AVR profile were left on, the VS, Site owner noted that the authentication works after this change. But if both ASM/Adv WAF Bot defense and Shape Security Defense iRule is configured on the VS, the site's authentication fails. Per the site owner, there were no changes in the Bot Defense or Shape Security Defense iRule configurations prior to the incident and that these configurations were in place way before the incident. Site owners shared the findings with their respective internal teams for their review. Resolution Afterwards, Site owner shared that their site now works as expected and authentication works for the web application with no changes done on both ASM/Adv WAF Bot defense and Shape Security Defense iRule on the site's VS. The cause of the authentication failure was undetermined. A theory on the possible cause of the issue was perhaps, there was another system inserting Javascript code in the responses and it might have affected the authentication process of the web application by prevented that portion of the site from loading. Additional Troubleshooting Notes The data gathered during the troubleshooting were the qkview and HTTPWatch capture - HAR files. It would help if a packet capture was taken along with the HTTPWatch capture while the issue was happening to have a full view of the issue. Decrypt the packet capture to observe HTTP exchanges and to correlate it with HTTPWatch capture events. The corresponding BIG-IP ASM/Adv WAF application event logs, Bot Defense or DoS protection logs will also be helpful in the correlation. Having a visual idea on how the Security Policy, Bot Defense or DoS protection profile are configured is also helpful - so its good to have a screenshot of these. It helps in analysis when there is complete data. Gathering the asmqkview with report and traffic data and corresponding ASM and AVR db dumps helps in the analysis. asmqkview -s0 --add-request-log --include-traffic-data -f /var/tmp/`/bin/hostname`_asmqkview_`date +%Y%m%d%H%M%S`.tgz #mysqldump -uroot -p`perl -I/ts/packages -MPassCrypt -nle 'print PassCrypt::decrypt_password($_)' /var/db/mysqlpw` DCC | gzip -9 > /shared/tmp/dcc.dump.gz # mysqldump -uroot -p`perl -I/ts/packages -MPassCrypt -nle 'print PassCrypt::decrypt_password($_)' /var/db/mysqlpw` PLC | gzip -9 > /shared/tmp/plc.dump.gz # mysqldump -uroot -p`perl -I/ts/packages -MPassCrypt -nle 'print PassCrypt::decrypt_password($_)' /var/db/mysqlpw` PRX | gzip -9 > /shared/tmp/prx.dump.gz # mysqldump -uroot -p`perl -I/ts/packages -MPassCrypt -nle 'print PassCrypt::decrypt_password($_)' /var/db/mysqlpw` logdb | gzip -9 > /shared/tmp/logdb.dump.gz It would also help if the systems in the path of the web application are known and whether it has features that may interfere with the features of BIG-IP ASM/Adv WAF or Shape Security Defense. Per the findings, there was a CDN that was injecting javascript code in the HTTP response and it may have contributed to the authentication failure for the end users. Isolate potentially conflicting features by removing one of them one at a time and observe the HTTP responses. Per the reference configuration, BIG-IP ASM/Adv WAF, Shape Security Defense, and BIG-IP AVR worked well prior to the incident. boomerang The injected javascript code noted in the ASM blocking page response was loaded from https[:]//s[.]go-mpulse[.]net/boomerang/. Checking this reference, it was related to https://github.com/akamai/boomerang. boomerang is a JavaScript library that measures the page load time experienced by real users, commonly called RUM (Real User Measurement). It has the ability to send this data back to your server for further analysis. With boomerang, you find out exactly how fast your users think your site is. In BIG-IP, the similar product we have is BIG-IP AVR - Application Visibility and Reporting (AVR) - where it collects "performance of web applications, with detailed views on HTTP and TCP stats, as well as system performance (CPU, memory, etc.)." Organizations may have specific needs on data that they need to collect from their site/web application and using a customizable solution such as boomerang can help. That's It For Now I hope this scenario review on Javascript-injecting systems effect on web application end users will be helpful on your next troubleshooting and hopefully gives you guidance on what data to gather and look for and troubleshooting options. The F5 SIRT creates security-related content posted here in DevCentral, sharing the team’s security mindset and knowledge. Feel free to view the articles that are tagged with the following: F5 SIRT series-F5SIRT-this-week-in-security TWIS
Access Page without resetting the session timer
I'm asking this question with the assumption that F5 is storing some kind of session timer, and resetting it each time the user makes an HTTP request. My application will have it's own session timer, set to be shorter than the F5. This is so I can pause their input progress in a friendly way to tell them they need to reauthenticate before F5's session ends and possibly makes them lose progress on their work. Our server will the the authoritative source of the users session time. The front end javascript will callback to an API on the server to resynchronize it's session time with the server. It will do this on an interval. Based on my assumptions, each one of those synchronize requests would cause the F5 session timer to reset. Since this requested is an automated process and not triggered by a user request, that session timer resetting is an undesirable side effect. Long explanation for a short question: How can I make my resynchronize calls to the server without causing the F5 to reset it's session time. Ideally these requests would still have the users EDIPI in the header. Is this possible?
No CAPTCHA - URL is not yet qualified for challenge injection
Hi, I am setting up Brute Force protection in ASM and have noted that I can get this drop traffic and alert, but when attempting to show the CAPTCHA, I only get the blocking page we have configured. The help notes that this occurs when the URL is not yet qualified for challenge injection, but the help also provides no details how to correct this. Can anyone assist? Assuming ASM policy: PolicyX and url: /LoginHere.aspx Thank you
Javascript REST API proxy with HTML UI, nodeJS and iControl module
Problem this snippet solves: 1) Provides browser interface to REST API. 2) Provides an all javascript inclusive app for managing BigIP objects. Enable/Disable/Add/Edit pool members. Only pool members for now. 3) Provides an API proxy via the use of Node.JS . Most scripts require an application or the CLI to launch or to integrate with. This app offers a GUI interface, in many ways similar to the BigIP GUI, rendered by a browser and served by Node. NodeJS connects to the BigIP and creates the dynamic pages which are rendered by browser. With NodeJS coming soon to the BigIP, this app could be installed on and served by the BigIP. How to use this snippet: Uses iControl proxy module from github, https://github.com/thwi/node-icontrol First Install node.js on one of your machines from: https://nodejs.org Next install the icontrol module: npm install icontrol To run this: 1) copy snippet and save to file: e.g. bigip_rest_proxy.js 2) start node: node bigip_rest_proxy.js <<This will start a web server listening on 8080 3) Securely Browse to https://ip_address_of_machine_ running_node:8080 This should work for 11.5 but I have only tested it in 11.6. Also Note that the credentials for the bigip are hard-coded for now. Sorry. To put your own, go ahead and change them inside the 'connect' function, lines 180-181. Code : 61606 Tested this on version: 11.6
What causes the TSbd/TSbp script to be inserted into the source code of a website?
In the source code of the website I work on I see that the script below is being inserted. <script type="text/javascript"> //<![CDATA[ window["_tsbp_"] = { ba : "X-TS-BP-Action", bh : "X-TS-AJAX-Request"}; //]]> </script><script type="text/javascript" src="/TSbd/08300f25d2ab20002940ca95b1a84050e4ba6d156f677a6f2819bde419b59b20e8b36a05eca4b390?type=2"></script> As we have AMP pages on our website which doesn't allow any custom JavaScript we would like to not get this script inserted. However, we are having some problems indentifying what exactly is causing this script to be inserted. We do run the WAF on our F5 and I suspect it's the culprit but I have been unable to confirm this. Also, I've been moving around some elements in the <head> tags and when I specifically move our scripts down to the bottom the TSbd/TSbp script is no longer being inserted. What I would like to know is what triggers the TSbd/TSbp script to be inserted. I am starting to think something on the F5 looks at the first X bytes of the page and then decides whether or not to insert the script. I would also like to know if there is more information about this topic available as I've not been able to find a lot. Maybe I am just not searching for the correct thing.
javascript fails with var is undefined
We use F5 with several upstream servers without SSL termination, and after our application update we faced some strange issues with undefined variables and pending xhr requests. Is there some advices for configuring F5 for slow and big server responses, does tcp-lan-optimized profile suitable for it?
SEC7111 HTTP Security Compromised Generated by a JavaScript.
Hey everyone! I just ran into an issue that I haven't seen before. Let me give you some background: We have a backend web application running only on port 80 and publish this through a standard HTTPS virtual server using only a Client SSL Profile. We have also a HTTP to HTTPS VS to make sure we access the site over HTTPS. Everything is working great except for a specific function on the site. The application is used to handle internal billing and once you are done with entering your details, you can print a report. When working correctly, this should open up the report as a PDF file in a new window. This is when things go south. Apparently there is a JavaScript that helps creating this PDF file. First we get the "Internet Explorer is not showing all of the content". When accepting that we get nothing. When checking the debugging you find this: The JavaScript is generating a URL of http:// when we have an active session running on https:// and security is being jeopardized. When going to the exact URL that reports the error but changing it to https:// it works straight away. So I know what the problem is but I have no idea how to fix it. Long term would be to turn on HTTPS on the back-end server but that will take some time and we need a fix for this quite fast since they cannot print out these reports if they are not in the local office, connecting to the server directly. I tried searching through the JavaScript to see if I can find where it actually uses http:// and just using a Stream Profile change it but I have not found anything. I also tried to add a Stream Profile changing Source: http://[URL] to Target: https://[URL] but that bricked the site. Since the problem is the JavaScript, the browser won't even send the request to the F5. If it were to send the request to the F5 it would hit the iRule and get redirected to HTTPS. Do you guys have any idea?
