Can I rely on fopen to execute a cURL operation with file upload securely?

Question

Can I rely on fopen to execute a cURL operation with file upload securely?

I have implemented an upload system that utilizes Dropbox's API to send files. The receiving .php file that performs a cURL operation looks like this:

$localFile = $_FILES["file_key"]['tmp_name'];
$fp = fopen($localFile, 'r');

$ch = curl_init();

curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_URL, 'https://content.dropboxapi.com/2/files/upload');
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    "authorization: Bearer MY-TOKEN",
    "content-type: application/octet-stream",
    "dropbox-api-arg: {\"path\": \"/tmp/a.txt\",\"mode\": \"add\",\"autorename\": true,\"mute\": false,\"strict_conflict\": false}"
));
curl_setopt($ch, CURLOPT_UPLOAD, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 86400); // Timeout of 1 Day
curl_setopt($ch, CURLOPT_INFILE, $fp);
curl_setopt($ch, CURLOPT_NOPROGRESS, false);
curl_setopt($ch, CURLOPT_BUFFERSIZE, 128);
curl_setopt($ch, CURLOPT_INFILESIZE, filesize($localFile));
curl_exec ($ch);

The above code works flawlessly, but I have some concerns about the usage of fopen in the second line. Is it considered a bad practice? Even though it is set to "read-only" mode, could it potentially allow malicious files to compromise my system?

php curl file-upload dropbox-api

Answer 1

Answer №1

Rest assured, PHP treats the data as purely informational and poses no security risks in this case. The curl function will seamlessly transmit it to the DropBox API without attempting any form of execution. It ultimately becomes DropBox's responsibility when dealing with user-uploaded content, and it is highly unlikely for them to execute any code unless they possess a significant vulnerability in their system.

Answer 2

Rest assured, PHP treats the data as purely informational and poses no security risks in this case. The curl function will seamlessly transmit it to the DropBox API without attempting any form of execution. It ultimately becomes DropBox's responsibility when dealing with user-uploaded content, and it is highly unlikely for them to execute any code unless they possess a significant vulnerability in their system.

Answer 3

Answer №2

It is perfectly secure as long as the read-only mode is enabled, ensuring that the file is only accessed for reading purposes and not executed.

Answer 4

It is perfectly secure as long as the read-only mode is enabled, ensuring that the file is only accessed for reading purposes and not executed.

Answer 5

Answer №3

it's the right approach to follow if you are using linux or MacOS* or *BSD and don't mind about windows compatibility, but allow me to nitpick on your code:

if you ever write any code that might run on windows, make it a habit to utilize fopen mode rb instead of r. This is because fopen mode r in windows could potentially corrupt binary data (and based on your octet-stream header, it seems like binary data). On the other hand, linux/macos/*BSD treat both r and rb modes the same way, so opt for the following line:

$fp = fopen($localFile, 'rb');

Moreover, this line

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    "authorization: Bearer MY-TOKEN",
    "content-type: application/octet-stream",
    "dropbox-api-arg: {\"path\": \"/tmp/a.txt\",\"mode\": \"add\",\"autorename\": true,\"mute\": false,\"strict_conflict\": false}"
));

should be written as:

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    "authorization: Bearer MY-TOKEN",
    "content-type: application/octet-stream",
    "dropbox-api-arg: " . json_encode(array(
        'path' => '/tmp/a.txt',
        'mode' => 'add',
        'autorename' => true,
        'mute' => false,
        'strict_conflict' => false,
    ))
));

This makes the code more legible, easier to maintain, and simpler to modify. However, I must mention that including this data as an HTTP HEADER was not a wise design choice by Dropbox. There are characters that are invalid in HTTP headers but legal in filenames according to most filesystem standards. This leads me to suspect that it is possible to create a valid JSON object containing a valid filename that cannot be properly encoded in an HTTP header format. In my opinion, Dropbox should have used multipart/form-data instead and treated the file and JSON as separate form variables.

Answer 6

it's the right approach to follow if you are using linux or MacOS* or *BSD and don't mind about windows compatibility, but allow me to nitpick on your code:

if you ever write any code that might run on windows, make it a habit to utilize fopen mode rb instead of r. This is because fopen mode r in windows could potentially corrupt binary data (and based on your octet-stream header, it seems like binary data). On the other hand, linux/macos/*BSD treat both r and rb modes the same way, so opt for the following line:

$fp = fopen($localFile, 'rb');

Moreover, this line

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    "authorization: Bearer MY-TOKEN",
    "content-type: application/octet-stream",
    "dropbox-api-arg: {\"path\": \"/tmp/a.txt\",\"mode\": \"add\",\"autorename\": true,\"mute\": false,\"strict_conflict\": false}"
));

should be written as:

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    "authorization: Bearer MY-TOKEN",
    "content-type: application/octet-stream",
    "dropbox-api-arg: " . json_encode(array(
        'path' => '/tmp/a.txt',
        'mode' => 'add',
        'autorename' => true,
        'mute' => false,
        'strict_conflict' => false,
    ))
));

This makes the code more legible, easier to maintain, and simpler to modify. However, I must mention that including this data as an HTTP HEADER was not a wise design choice by Dropbox. There are characters that are invalid in HTTP headers but legal in filenames according to most filesystem standards. This leads me to suspect that it is possible to create a valid JSON object containing a valid filename that cannot be properly encoded in an HTTP header format. In my opinion, Dropbox should have used multipart/form-data instead and treated the file and JSON as separate form variables.

Can I rely on fopen to execute a cURL operation with file upload securely?

Answer №1

Answer №2

Answer №3

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