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medium severity

Uninitialized Memory Exposure

  • Vulnerable module: concat-stream
  • Introduced through: concat-stream@1.2.0

Detailed paths

  • Introduced through: concat-stream@1.2.0
    Remediation: Upgrade to concat-stream@1.3.2.


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