GHSA-99f9-gv72-fw9r
MEDIUMBref Doesn't Support Multiple Value Headers in ApiGatewayFormatV2
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
bref/brefReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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.phpfile 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.ymlto 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.phpscript 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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | bref/bref | all versions | 2.1.13 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for bref/bref. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update bref/bref to 2.1.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-99f9-gv72-fw9r is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-99f9-gv72-fw9r is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-99f9-gv72-fw9r. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-99f9-gv72-fw9r in your dependencies?
O3 detects GHSA-99f9-gv72-fw9r across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.