TSLint security rules

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TSLint security rules

Inspired by eslint-plugin-security

How to use

  • Install package:
npm i tslint-config-security --save-dev  --production

  • Update your tslint.json:

  "extends": ["tslint-config-security"]

By default tslint-config-security enables all rules, but you may disable any of them (not recommended):
  "extends": ["tslint-config-security"],
  "rules": {
    "tsr-detect-html-injection": false,
    "tsr-detect-unsafe-regexp": false


All rules start from the prefix tsr- (TSLint Security Rule) to prevent name collisions.


Locates potentially unsafe regular expressions, which may take a very long time to run, blocking the event loop.
Examples: test/rules/tsr-detect-unsafe-regexp/default/test.ts.lint
More information:
  • https://web.archive.org/web/20170131192028/https://blog.liftsecurity.io/2014/11/03/regular-expression-dos-and-node.js#regular-expression-dos-and-nodejs
  • https://snyk.io/blog/redos-and-catastrophic-backtracking


Detects variable in new Buffer argument
Examples: test/rules/tsr-detect-non-literal-buffer/default/test.ts.lint


Detects calls to Buffer with noAssert flag set
From the Node.js API docs: "Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer."
Examples: test/rules/tsr-detect-buffer-noassert/default/test.ts.lint


Detects instances of child_process & non-literal exec()
More information: https://web.archive.org/web/20170129010544/https://blog.liftsecurity.io/2014/08/19/Avoid-Command-Injection-Node.js#avoiding-command-injection-in-nodejs
Examples: test/rules/tsr-detect-child-process/default/test.ts.lint


Detects object.escapeMarkup = false, which can be used with some template engines to disable escaping of HTML entities. This can lead to Cross-Site Scripting (XSS) vulnerabilities.
More information: https://www.owasp.org/index.php/Cross-siteScripting(XSS)
Examples: test/rules/tsr-disable-mustache-escape/default/test.ts.lint


Detects eval(variable) which can allow an attacker to run arbitrary code inside your process.
More information: http://security.stackexchange.com/questions/94017/what-are-the-security-issues-with-eval-in-javascript
Examples: test/rules/tsr-detect-eval-with-expression/default/test.ts.lint


Detects Express csrf middleware setup before method-override middleware. This can allow GET requests (which are not checked by csrf) to turn into POST requests later.
More information: http://blog.nibblesec.org/2014/05/nodejs-connect-csrf-bypass-abusing.html
Examples: test/rules/tsr-detect-no-csrf-before-method-override/default/test.ts.lint


Detects variable in filename argument of fs calls, which might allow an attacker to access anything on your system.
More information: https://www.owasp.org/index.php/PathTraversal
Known limitations
Due to the known issues in the typed TSLint rules:
  • https://github.com/Microsoft/vscode-tslint/issues/70
  • https://github.com/Microsoft/vscode-tslint/blob/master/tslint/README.md#how-can-i-use-tslint-rules-that-require-type-information
  • https://github.com/Microsoft/vscode-tslint/issues/70

tslint-config-security module will analyze methods only on fs variable or on 'fs' module. E.g.:
const fs = require('fs');

fs.open(somePath); // triggers the error
require('fs').symlink(path1, path2); // triggers the error
require("fs").symlink(path1, path2); // triggers the error

const myFs = require('fs');

myFs.open(somePath); // no error

More examples: test/rules/tsr-detect-non-literal-fs-filename/default/test.ts.lint


Detects RegExp(variable), which might allow an attacker to DOS your server with a long-running regular expression.
More information:
  • https://web.archive.org/web/20170131192028/https://blog.liftsecurity.io/2014/11/03/regular-expression-dos-and-node.js#regular-expression-dos-and-nodejs

Examples: test/rules/tsr-detect-non-literal-regexp/default/test.ts.lint


Detects require(variable), which might allow an attacker to load and run arbitrary code, or access arbitrary files on disk.
More information:
  • http://www.bennadel.com/blog/2169-where-does-node-js-and-require-look-for-modules.htm
  • https://github.com/benmosher/eslint-plugin-import/blob/master/docs/rules/no-dynamic-require.md

Examples: test/rules/tsr-detect-non-literal-require/default/test.ts.lint


Detects insecure comparisons (==, !=, !== and ===), which check input sequentially.
More information: https://snyk.io/blog/node-js-timing-attack-ccc-ctf/
Examples: test/rules/tsr-detect-possible-timing-attacks/default/test.ts.lint


Detects if pseudoRandomBytes() is in use, which might not give you the randomness you need and expect.
More information: http://stackoverflow.com/questions/18130254/randombytes-vs-pseudorandombytes
Examples: test/rules/tsr-detect-pseudo-random-bytes/default/test.ts.lint


Detects HTML injections:
  • document.write(variable)
  • document.writeln(variable)
  • Element.innerHTML = variable;
  • Element.outerHTML = variable;
  • el.insertAdjacentHTML(variable);

More examples: test/rules/tsr-detect-html-injection/default/test.ts.lint


Detects possible SQL injections in string literals:
// invalid
const userId = 1;
const query1 = `SELECT * FROM users WHERE id = ${userId}`;
const query2 = `SELECT * FROM users WHERE id = ` + userId;
const query3 = 'SELECT * FROM users WHERE id =' + userId;

const columns = 'id, name';
Users.query(`SELECT ${columns} FROM users`);

// valid
const userId = 1;
const query = sql`SELECT * FROM users WHERE id = ${userId}`;

// See https://github.com/mysqljs/mysql
db.query('SELECT * FROM `books` WHERE `author` = ?', ['David'], function (error, results, fields) {

More examples: test/rules/tsr-detect-sql-literal-injection/default/test.ts.lint


Detects when all windows & frames on your page (including ones that were injected by 3rd-party scripts) may receive your data.
Always provide a specific targetOrigin, not , if you know where the other window's document should be located. Failing to provide a specific target discloses the data you send to any interested malicious site. https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage

const myWindow = document.getElementById('myIFrame').contentWindow;

myWindow.postMessage(message, "*"); // Noncompliant


Detects a potential unsafe access to the object properties

It equals to `new Function(prop3)`

const a = {};

// unsafe

// unsafe

More information:
  • use Map
  • use .hasOwnProperty check
  • use Content-Security-Policy on your page