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high severity

Uninitialized Memory Exposure

  • Vulnerable module: base64url
  • Introduced through: base64url@0.0.3 and jwa@0.0.1

Detailed paths

  • Introduced through: jws@0.2.2 base64url@0.0.3
    Remediation: Upgrade to jws@3.1.5.
  • Introduced through: jws@0.2.2 jwa@0.0.1 base64url@0.0.6
    Remediation: Upgrade to jws@3.1.0.


base64url Converting to, and from, base64url.

Affected versions of this package are vulnerable to Uninitialized Memory Exposure. An attacker could extract sensitive data from uninitialized memory or may cause a Denial of Service (DoS) by passing in a large number, in setups where typed user input can be passed (e.g. from JSON).


The Buffer class on Node.js is a mutable array of binary data, and can be initialized with a string, array or number.

const buf1 = new Buffer([1,2,3]);
// creates a buffer containing [01, 02, 03]
const buf2 = new Buffer('test');
// creates a buffer containing ASCII bytes [74, 65, 73, 74]
const buf3 = new Buffer(10);
// creates a buffer of length 10

The first two variants simply create a binary representation of the value it received. The last one, however, pre-allocates a buffer of the specified size, making it a useful buffer, especially when reading data from a stream. When using the number constructor of Buffer, it will allocate the memory, but will not fill it with zeros. Instead, the allocated buffer will hold whatever was in memory at the time. If the buffer is not zeroed by using buf.fill(0), it may leak sensitive information like keys, source code, and system info.


Upgrade base64url to version 3.0.0 or higher. Note This is vulnerable only for Node <=4


high severity

Forgeable Public/Private Tokens

  • Vulnerable module: jws
  • Introduced through: jws@0.2.2

Detailed paths

  • Introduced through: jws@0.2.2
    Remediation: Upgrade to jws@3.0.0.


jws is an implementation of JSON Web Signatures. Affected versions of this package are vulnerable to an Authentication Bypass attack, due to the "algorithm" not being enforced in jws.verify(). Attackers are given the opportunity to choose the algorithm sent to the server and generate signatures with arbitrary contents. The server expects an asymmetric key (RSA) but is sent a symmetric key (HMAC-SHA) with RSA's public key, so instead of going through a key validation process, the server will think the public key is actually an HMAC private key.


Upgrade jws to version 3.0.0 or later.


medium severity

Regular Expression Denial of Service (ReDoS)

  • Vulnerable module: uglify-js
  • Introduced through: tap@0.3.3 and base64url@0.0.3

Detailed paths

  • Introduced through: jws@0.2.2 tap@0.3.3 runforcover@0.0.2 bunker@0.1.2 burrito@0.2.12 uglify-js@1.1.1
  • Introduced through: jws@0.2.2 base64url@0.0.3 tap@0.3.3 runforcover@0.0.2 bunker@0.1.2 burrito@0.2.12 uglify-js@1.1.1


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.