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