post: Convert AWS WAF ACLs to human-readable format

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Ming Di Leom 2021-06-27 07:53:55 +00:00
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---
title: Convert AWS WAF ACLs to human-readable format
excerpt: Run the attached script to download and convert ACLs
date: 2021-06-27
tags:
- aws
- security
---
I regularly need to audit my company's access control lists (ACLs) implemented in AWS WAF, as part of my job. Each ACL can be more than a thousand lines which is practically impossible to read. I wrote a script that downloads and summarises the ACLs into human-readable format; each one-thousand-line behemoth is transformed into a fifty-line summary that I can _actually_ audit.
The script is [available here](/files/20210627/waf-acl.py). It currently only supports Cloudfront ACL, feel free to extend it to support regional ACL.
```
./waf-acl.py {profile-name} --directory output-dir --original
```
**profile-name**: The profile name as listed in "~/.aws/credentials".
**directory**: Output directory. It will be created if not exist. Defaults to current folder.
**original**: Preserve the original ACL after conversion and save it with "-original" suffix.
## ACL schema
The underlying format of a web ACL is JSON. In this use case, I'm only concern with two keys:
``` json
{
"Name": "",
"Rules": [
{
"Name": "",
"Statement": {},
"Action": {
"Block": {}
}
},
{
"Name": "",
"Statement": {},
"Action": {
"Allow": {}
}
}]
}
```
The script names each ACL according to the value of "Name". "Rules" is an array of objects, where each object represents a rule. Each rule has an [action](https://docs.aws.amazon.com/waf/latest/developerguide/waf-rule-action.html) of count, allow or block.
In each rule, there is a statement and it functions as a matching condition. Each [statement](https://docs.aws.amazon.com/waf/latest/developerguide/waf-rule-statements-list.html) can contain one or match statements combined using logical rule (AND, NOT, OR).
## Converted schema
A converted ACL has an array of objects, each object has three keys.
``` json
[
{
"Name": "",
"Action": "",
"Rule": ""
}
]
```
## And/OrStatement
``` json Original
{
"Name": "ruleA",
"Statement": {
"OrStatement": {
"Statements": [
{
"foo": {}
},
{
"bar": {}
}
]
}
}
}
```
``` json Converted
{
"ruleA": "foo OR bar"
}
```
## Nested And/OrStatement
``` json Original
{
"Name": "ruleA",
"Statement": {
"AndStatement": {
"Statements": [
{
"OrStatement": {
"Statements": [
{
"foo": {}
},
{
"bar": {}
}
]
}
},
{
"baz": {}
}
]
}
}
}
```
``` json Converted
{
"ruleA": "(foo OR bar) AND baz"
}
```
## NotStatement
``` json Original
{
"Name": "ruleA",
"Statement": {
"NotStatement": {
"Statement": {
"foo": {}
}
}
}
}
```
``` json Converted
{
"ruleA": "NOT foo"
}
```
## String match
``` json Orignal
{
"ByteMatchStatement": {
"SearchString": ".conf",
"FieldToMatch": {
"UriPath": {}
},
"PositionalConstraint": "ENDS_WITH"
}
}
```
``` plain Converted
UriPath=ENDSWITH(.conf)
```