Headline
GHSA-99f9-gv72-fw9r: Bref Doesn't Support Multiple Value Headers in ApiGatewayFormatV2
Impacted Resources
bref/src/Event/Http/HttpResponse.php:61-90
Description
When Bref is used in combination with an API Gateway with the v2 format, it does not handle multiple values headers.
Precisely, if PHP generates a response with two headers having the same key but different values only the latest one is kept.
Impact
If an application relies on multiple headers with the same key being set for security reasons, then Bref would lower the application security.
For example, if an application sets multiple Content-Security-Policy
headers, then Bref would just reflect the latest one.
PoC
- Create a new Bref project.
- Create an
index.php
file with the following content:
<?php
header("Content-Security-Policy: script-src 'none'", false);
header("Content-Security-Policy: img-src 'self'", false);
?>
<script>alert(document.domain)</script>
<img src="https://bref.sh/favicon-32x32.png">
- Use the following
serverless.yml
to deploy the Lambda:
service: app
provider:
name: aws
region: eu-central-1
plugins:
- ./vendor/bref/bref
functions:
api:
handler: index.php
description: ''
runtime: php-81-fpm
timeout: 28 # in seconds (API Gateway has a timeout of 29 seconds)
events:
- httpApi: '*'
# Exclude files from deployment
package:
patterns:
- '!node_modules/**'
- '!tests/**'
- Browse the Lambda URL.
- Notice that the JavaScript code is executed as the
Content-Security-Policy: script-src 'none'
header has been removed. - Notice that the external image has not been loaded as the
Content-Security-Policy: img-src 'self'
header has been kept. - Start a PHP server inside the project directory (e.g.
php -S 127.0.0.1:8090
). - Browse the
index.php
script through the PHP server (e.g. http://127.0.0.1:8090/index.php). - Notice that the JavaScript code is not executed as the
Content-Security-Policy: script-src 'none'
header has been kept. - Notice that the external image has not been loaded as the
Content-Security-Policy: img-src 'self'
header has been kept.
Suggested Remediation
Concatenate all the multiple value headers’ values with a comma (,
) as separator and return a single header with all the values to the API Gateway.
References
- https://www.rfc-editor.org/rfc/rfc9110.html#section-5.2
- GitHub Advisory Database
- GitHub Reviewed
- CVE-2024-24753
Bref Doesn’t Support Multiple Value Headers in ApiGatewayFormatV2
Moderate severity GitHub Reviewed Published Feb 1, 2024 in brefphp/bref • Updated Feb 1, 2024
Package
Affected versions
< 2.1.13
Impacted Resources
bref/src/Event/Http/HttpResponse.php:61-90
Description
When Bref is used in combination with an API Gateway with the v2 format, it does not handle multiple values headers.
Precisely, if PHP generates a response with two headers having the same key but different values only the latest one is kept.
Impact
If an application relies on multiple headers with the same key being set for security reasons, then Bref would lower the application security.
For example, if an application sets multiple Content-Security-Policy headers, then Bref would just reflect the latest one.
PoC
- Create a new Bref project.
- Create an index.php file with the following content:
<?php header("Content-Security-Policy: script-src 'none’", false); header("Content-Security-Policy: img-src 'self’", false); ?> <script>alert(document.domain)</script> <img src="https://bref.sh/favicon-32x32.png">
- Use the following serverless.yml to deploy the Lambda:
service: app
provider: name: aws region: eu-central-1
plugins: - ./vendor/bref/bref
functions: api: handler: index.php description: ‘’ runtime: php-81-fpm timeout: 28 # in seconds (API Gateway has a timeout of 29 seconds) events: - httpApi: ‘*’
Exclude files from deployment
package: patterns: - ‘!node_modules/**’ - ‘!tests/**’
- Browse the Lambda URL.
- Notice that the JavaScript code is executed as the Content-Security-Policy: script-src ‘none’ header has been removed.
- Notice that the external image has not been loaded as the Content-Security-Policy: img-src ‘self’ header has been kept.
- Start a PHP server inside the project directory (e.g. php -S 127.0.0.1:8090).
- Browse the index.php script through the PHP server (e.g. http://127.0.0.1:8090/index.php).
- Notice that the JavaScript code is not executed as the Content-Security-Policy: script-src ‘none’ header has been kept.
- Notice that the external image has not been loaded as the Content-Security-Policy: img-src ‘self’ header has been kept.
Suggested Remediation
Concatenate all the multiple value headers’ values with a comma (,) as separator and return a single header with all the values to the API Gateway.
References
- https://www.rfc-editor.org/rfc/rfc9110.html#section-5.2
References
- GHSA-99f9-gv72-fw9r
- https://nvd.nist.gov/vuln/detail/CVE-2024-24753
- brefphp/bref@f834027
- https://github.com/brefphp/bref/blob/2.1.12/src/Event/Http/HttpResponse.php#L61-L90
Published to the GitHub Advisory Database
Feb 1, 2024