Re: AWS Web Application Firewall blocks ISP ranges?

[Martin Tonusoo <martin () tonusoo ee>]

Hi.

Our experience from last month was quite similar to what others have
already described. Based on our tests all the allocations associated
with our ASN were added to "HostingProviderIPList". At first we tried
to reach the AWS by e-mail, but received no response. Once we opened a
ticket(we are both the AWS customer and a Direct Connect Delivery
partner) and explained that our address space is not solely used for
hosting services, then all our networks were whitelisted within few
days. We even had a call with AWS support team and they seemed to be
well aware about false positives in the "HostingProviderIPList". In
other words, we were clearly not a first ISP complaining.

Final update to our ticket from the AWS Support Engineering department
was following:

"I would like to inform you that as per the update I got from our
internal team, the IP Data which we use for our rules is provided by a
third party and changes frequently. Moving ahead I would like to
request you to kindly check your setup and see if you can separate the
network ranges reserved for any hosting type services in your ASN and
provide that to us so that we can check if we can allow the range
which is not used for hosting type services."

It's unfortunate that Amazon continues to offer this service despite
their underlying IP address data having a low level of granularity,
and they are well aware of the problems it causes for address owners.


AWS Web Application Firewall for testing purposes can be build for
example like this:

1) created a VPC("VPC only") with "IPv4 CIDR" 10.0.0.0/24
2) created a subnet 10.0.0.0/28 in one availability zone(for example
"eu-north-1a") and a subnet 10.0.0.16/28 in another availability
zone(for example "eu-north-1b")
3) launched an Ubuntu EC2 instance("t3.micro", free tier eligible).
Auto-assigned the public IP. Allowed SSH and HTTP traffic from
anywhere.
4) created an "Internet gateway" and attached it to VPC
5) added a default route to route table and pointed it to Internet gateway
6) installed(sudo apt update && sudo apt install apache2 -y) a web
server in Ubuntu VM
7) tested with "curl http://51.20.94.186"; where 51.20.94.186 is the
public IP address automatically assigned to EC2 instance
8) created a "Target group" for "Instances" type target which is
associated with VPC created earlier. Protocol:Port configuration has
to be HTTP:80.
9) created an Internet-facing "Application Load balancer" and mapped
it with two subnets created previously in two different availability
zones. Load balancer has to forward to target group created in the
previous step.
10) created a WAF and associate it with Application Load Balancer
11) used an AWS managed rule group named "Anonymous IP list" in WAF.
This includes the notorious "HostingProviderIPList" with a default
rule action of "Block".
12) "curl http://test-213161342.eu-north-1.elb.amazonaws.com"; returns
"HTTP/1.1 403" from the networks included in the
"HostingProviderIPList". DNS name is seen on the load balancer details
page.


P.S. Previous thread on AWS WAF was
https://mailman.nanog.org/pipermail/nanog/2024-February/224931.html


Martin