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Inadequate file size control

Description​

The system does not perform an adequate control of the size of the files that can be uploaded to the server.

Impact​

  • Consume server resources and storage to upload large files.
  • Lead to denial of service attacks if the server storage capacity is overloaded.

Recommendation​

Implement controls to limit the maximum file size that can be uploaded to the server.

Threat​

Authenticated attacker on the Internet.

Expected Remediation Time​

⌚ 30 minutes.

Score​

Default score using CVSS 3.1. It may change depending on the context of the vulnerability.

Base​

  • Attack vector: N
  • Attack complexity: L
  • Privileges required: L
  • User interaction: N
  • Scope: U
  • Confidentiality: N
  • Integrity: N
  • Availability: H

Temporal​

  • Exploit code madurity: P
  • Remediation level: O
  • Report confidence: C

Result​

  • Vector string: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H/E:P/RL:O/RC:C
  • Score:
    • Base: 6.5
    • Temporal: 5.9
  • Severity:
    • Base: Medium
    • Temporal: Medium

Code Examples​

Compliant code​

The file size is set to a strict limit based on business needs

var storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, "uploads")
  },
  filename: function (req, file, cb) {
    cb(null, file.fieldname + "-" + Date.now()+".jpg")
  }
})

// Define the maximum size for uploading
// picture i.e. 1 MB. it is optional
const maxSize = 1 * 1000 * 1000;

var upload = multer({
  storage: storage,
  limits: { fileSize: maxSize },
  fileFilter: function (req, file, cb){
    var filetypes = /jpeg|jpg|png/;
    var mimetype = filetypes.test(file.mimetype);
    var extname = filetypes.test(path.extname(file.originalname).toLowerCase());
}).single("mypic");

Non compliant code​

There is no server side validation of file size before uploading it to the server

var storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, "uploads")
  },
  filename: function (req, file, cb) {
    cb(null, file.fieldname + "-" + Date.now()+".jpg")
  }
})

var upload = multer({
  storage: storage,
  fileFilter: function (req, file, cb){
    var filetypes = /jpeg|jpg|png/;
    var mimetype = filetypes.test(file.mimetype);
    var extname = filetypes.test(path.extname(file.originalname).toLowerCase());
}).single("mypic");

Requirements​

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