Uninitialized Memory Exposure Affecting bl package, versions <0.9.5 >=1.0.0 <1.0.1



    Attack Complexity High
    Confidentiality High

    Threat Intelligence

    Exploit Maturity Mature

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  • Snyk ID npm:bl:20160119
  • published 18 Sep 2016
  • disclosed 19 Jan 2016
  • credit Feross Aboukhadijeh

Introduced: 19 Jan 2016

CVE NOT AVAILABLE CWE-201 Open this link in a new tab


bl is a storage object for collections of Node Buffers.

A possible memory disclosure vulnerability exists when a value of type number is provided to the append() method and results in concatenation of uninitialized memory to the buffer 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');

bl's append 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.

const BufferList = require('bl')

var bl = new BufferList() bl.append(new Buffer('abcd')) bl.append(new Buffer('efg')) bl.append('100') // appends a Buffer holding 100 bytes of uninitialized memory bl.append(100)
bl.append(new Buffer('j'))

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

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

Note This is vulnerable only for Node <=4