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high severity

Insecure Randomness

  • Vulnerable module: crypto-browserify
  • Introduced through: browserify@2.17.4

Detailed paths

  • Introduced through: bungee@0.0.6 browserify@2.17.4 browser-resolve@0.1.1 crypto-browserify@0.2.1


crypto-browserify is implementation of crypto for the browser.

Affected versions of the package are vulnerable to Insecure Randomness due to using the cryptographically insecure Math.random(). This function can produce predictable values and should not be used in security-sensitive context.


Computers are deterministic machines, and as such are unable to produce true randomness. Pseudo-Random Number Generators (PRNGs) approximate randomness algorithmically, starting with a seed from which subsequent values are calculated.

There are two types of PRNGs: statistical and cryptographic. Statistical PRNGs provide useful statistical properties, but their output is highly predictable and forms an easy to reproduce numeric stream that is unsuitable for use in cases where security depends on generated values being unpredictable. Cryptographic PRNGs address this problem by generating output that is more difficult to predict. For a value to be cryptographically secure, it must be impossible or highly improbable for an attacker to distinguish between it and a truly random value. In general, if a PRNG algorithm is not advertised as being cryptographically secure, then it is probably a statistical PRNG and should not be used in security-sensitive contexts.

You can read more about node's insecure Math.random() in Mike Malone's post.


Upgrade crypto-browserify to version 2.1.11 or higher.


high severity

Command Injection

  • Vulnerable module: shell-quote
  • Introduced through: browserify@2.17.4

Detailed paths

  • Introduced through: bungee@0.0.6 browserify@2.17.4 shell-quote@0.0.1
    Remediation: Upgrade to browserify@12.0.0.


shell-quote is a package used to quote and parse shell commands.

Affected versions of this package are vulnerable to Command Injection. The quote function does not properly escape the following special characters <, >, ;, {, } , and as a result can be used by an attacker to inject malicious shell commands or leak sensitive information.

Proof of Concept

Consider the following poc.js application

var quote = require('shell-quote').quote;
var exec = require('child_process').exec;

var userInput = process.argv[2];

var safeCommand = quote(['echo', userInput]);

exec(safeCommand, function (err, stdout, stderr) {

Running the following command will not only print the character a as expected, but will also run the another command, i.e touch malicious.sh

$ node poc.js 'a;{touch,malicious.sh}'


Upgrade shell-quote to version 1.6.1 or higher.


high severity

Improper minification of non-boolean comparisons

  • Vulnerable module: uglify-js
  • Introduced through: browserify@2.17.4

Detailed paths

  • Introduced through: bungee@0.0.6 browserify@2.17.4 umd@1.1.1 uglify-js@2.2.5
    Remediation: Upgrade to browserify@2.34.0.
  • Introduced through: bungee@0.0.6 browserify@2.17.4 umd@1.1.1 ruglify@1.0.0 uglify-js@2.2.5
    Remediation: Open PR to patch uglify-js@2.2.5.


uglify-js is a JavaScript parser, minifier, compressor and beautifier toolkit.

Tom MacWright discovered that UglifyJS versions 2.4.23 and earlier are affected by a vulnerability which allows a specially crafted Javascript file to have altered functionality after minification. This bug was demonstrated by Yan to allow potentially malicious code to be hidden within secure code, activated by minification.


In Boolean algebra, DeMorgan's laws describe the relationships between conjunctions (&&), disjunctions (||) and negations (!). In Javascript form, they state that:

 !(a && b) === (!a) || (!b)
 !(a || b) === (!a) && (!b)

The law does not hold true when one of the values is not a boolean however.

Vulnerable versions of UglifyJS do not account for this restriction, and erroneously apply the laws to a statement if it can be reduced in length by it.

Consider this authentication function:

function isTokenValid(user) {
    var timeLeft =
        !!config && // config object exists
        !!user.token && // user object has a token
        !user.token.invalidated && // token is not explicitly invalidated
        !config.uninitialized && // config is initialized
        !config.ignoreTimestamps && // don't ignore timestamps
        getTimeLeft(user.token.expiry); // > 0 if expiration is in the future

    // The token must not be expired
    return timeLeft > 0;

function getTimeLeft(expiry) {
  return expiry - getSystemTime();

When minified with a vulnerable version of UglifyJS, it will produce the following insecure output, where a token will never expire:

( Formatted for readability )

function isTokenValid(user) {
    var timeLeft = !(                       // negation
        !config                             // config object does not exist
        || !user.token                      // user object does not have a token
        || user.token.invalidated           // token is explicitly invalidated
        || config.uninitialized             // config isn't initialized
        || config.ignoreTimestamps          // ignore timestamps
        || !getTimeLeft(user.token.expiry)  // > 0 if expiration is in the future
    return timeLeft > 0

function getTimeLeft(expiry) {
    return expiry - getSystemTime()


Upgrade UglifyJS to version 2.4.24 or higher.


medium severity

Uninitialized Memory Exposure

  • Vulnerable module: concat-stream
  • Introduced through: browserify@2.17.4

Detailed paths

  • Introduced through: bungee@0.0.6 browserify@2.17.4 browser-resolve@0.1.1 http-browserify@0.1.11 concat-stream@0.0.8
  • Introduced through: bungee@0.0.6 browserify@2.17.4 concat-stream@0.1.1
    Remediation: Upgrade to browserify@3.17.0.
  • Introduced through: bungee@0.0.6 browserify@2.17.4 module-deps@0.10.3 concat-stream@1.0.1
    Remediation: Upgrade to browserify@3.17.0.


concat-stream is writable stream that concatenates strings or binary data and calls a callback with the result. Affected versions of the package are vulnerable to Uninitialized Memory Exposure.

A possible memory disclosure vulnerability exists when a value of type number is provided to the stringConcat() method and results in concatenation of uninitialized memory to the stream collection.

This is a result of unobstructed use of the Buffer constructor, whose insecure default constructor increases the odds of memory leakage.


Constructing a Buffer class with integer N creates a Buffer of length N with raw (not "zero-ed") memory.

In the following example, the first call would allocate 100 bytes of memory, while the second example will allocate the memory needed for the string "100":

// uninitialized Buffer of length 100
x = new Buffer(100);
// initialized Buffer with value of '100'
x = new Buffer('100');

concat-stream's stringConcat function uses the default Buffer constructor as-is, making it easy to append uninitialized memory to an existing list. If the value of the buffer list is exposed to users, it may expose raw server side memory, potentially holding secrets, private data and code. This is a similar vulnerability to the infamous Heartbleed flaw in OpenSSL.

You can read more about the insecure Buffer behavior on our blog.

Similar vulnerabilities were discovered in request, mongoose, ws and sequelize.


Upgrade concat-stream to version 1.5.2 or higher. Note This is vulnerable only for Node <=4


medium severity

Prototype Pollution

  • Vulnerable module: minimist
  • Introduced through: optimist@0.6.1

Detailed paths

  • Introduced through: bungee@0.0.6 optimist@0.6.1 minimist@0.0.10


minimist is a parse argument options module.

Affected versions of this package are vulnerable to Prototype Pollution. The library could be tricked into adding or modifying properties of Object.prototype using a constructor or __proto__ payload.

PoC by Snyk

require('minimist')('--__proto__.injected0 value0'.split(' '));
console.log(({}).injected0 === 'value0'); // true

require('minimist')('--constructor.prototype.injected1 value1'.split(' '));
console.log(({}).injected1 === 'value1'); // true


Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as _proto_, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

  • Unsafe Object recursive merge

  • Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])


      target[property] = source[property]

When the source object contains a property named _proto_ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to _proto_.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Type Origin Short description
Denial of service (DoS) Client This is the most likely attack.
DoS occurs when Object holds generic functions that are implicitly called for various operations (for example, toString and valueOf).
The attacker pollutes Object.prototype.someattr and alters its state to an unexpected value such as Int or Object. In this case, the code fails and is likely to cause a denial of service.
For example: if an attacker pollutes Object.prototype.toString by defining it as an integer, if the codebase at any point was reliant on someobject.toString() it would fail.
Remote Code Execution Client Remote code execution is generally only possible in cases where the codebase evaluates a specific attribute of an object, and then executes that evaluation.
For example: eval(someobject.someattr). In this case, if the attacker pollutes Object.prototype.someattr they are likely to be able to leverage this in order to execute code.
Property Injection Client The attacker pollutes properties that the codebase relies on for their informative value, including security properties such as cookies or tokens.
For example: if a codebase checks privileges for someuser.isAdmin, then when the attacker pollutes Object.prototype.isAdmin and sets it to equal true, they can then achieve admin privileges.

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

  • Application server

  • Web server

How to prevent

  1. Freeze the prototype— use Object.freeze (Object.prototype).

  2. Require schema validation of JSON input.

  3. Avoid using unsafe recursive merge functions.

  4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

  5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Oliver. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018


Upgrade minimist to version 0.2.1, 1.2.3 or higher.


medium severity

Potential Script Injection

  • Vulnerable module: syntax-error
  • Introduced through: browserify@2.17.4

Detailed paths

  • Introduced through: bungee@0.0.6 browserify@2.17.4 syntax-error@0.0.1
    Remediation: Upgrade to browserify@3.33.0.


There was a security vulnerability where a malicious file could execute code when browserified. Make sure your installation of browserify is using syntax-error@1.1.1 or later.

Source: Node Security Project


The vulnerability involves breaking out of Function(), which was used to check syntax for more informative errors. In node 0.10, Function() seems to be implemented in terms of eval(), so malicious code can execute even if the function returned by Function() was never called. node 0.11 does not appear to be vulnerable.

Thanks to [Cal Leeming] (cal@iops.io) for discovering and disclosing this bug!


Update to version 1.1.1 or greater. If this is being used in conjunction with browserify, update browserify to 4.2.1 or greater.


medium severity

Regular Expression Denial of Service (ReDoS)

  • Vulnerable module: uglify-js
  • Introduced through: browserify@2.17.4

Detailed paths

  • Introduced through: bungee@0.0.6 browserify@2.17.4 umd@1.1.1 uglify-js@2.2.5
    Remediation: Upgrade to browserify@9.0.0.
  • Introduced through: bungee@0.0.6 browserify@2.17.4 umd@1.1.1 ruglify@1.0.0 uglify-js@2.2.5
    Remediation: Open PR to patch uglify-js@2.2.5.


The parse() function in the uglify-js package prior to version 2.6.0 is vulnerable to regular expression denial of service (ReDoS) attacks when long inputs of certain patterns are processed.


Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.

The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.

Let’s take the following regular expression as an example:

regex = /A(B|C+)+D/

This regular expression accomplishes the following:

  • A The string must start with the letter 'A'
  • (B|C+)+ The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the + matches one or more times). The + at the end of this section states that we can look for one or more matches of this section.
  • D Finally, we ensure this section of the string ends with a 'D'

The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD

It most cases, it doesn't take very long for a regex engine to find a match:

0.04s user 0.01s system 95% cpu 0.052 total

1.79s user 0.02s system 99% cpu 1.812 total

The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.

Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.

Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:

  1. CCC
  2. CC+C
  3. C+CC
  4. C+C+C.

The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.

From there, the number of steps the engine must use to validate a string just continues to grow.

String Number of C's Number of steps
ACCCX 3 38

By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.


Upgrade to version 2.6.0 or greater. If a direct dependency update is not possible, use snyk wizard to patch this vulnerability.