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Date: Fri, 23 Dec 2016 08:38:15 +0100 (CET)
From: Daniel Stenberg <>
To: curl security announcements -- curl users <>,,
        libcurl hacking <>,
Subject: [SECURITY ADVISORY] curl: uninitialized random

uninitialized random

Project curl Security Advisory, December 23, 2016 -


libcurl's (new) internal function that returns a good 32bit random value was
implemented poorly and overwrote the pointer instead of writing the value into
the buffer the pointer pointed to.

This random value is used to generate nonces for Digest and NTLM
authentication, for generating boundary strings in HTTP formposts and
more. Having a weak or virtually non-existent random there makes these
operations vulnerable.

This function is brand new in 7.52.0 and is the result of an overhaul to make
sure libcurl uses strong random as much as possible - provided by the backend
TLS crypto libraries when present. The faulty function was introduced in [this

We are not aware of any exploit of this flaw.


This mistake managed to slip in because:

  1. It wasn't detected by manual code reviews

  2. When libcurl is built debug-enabled (which is often the case when libcurl
     developers build it), the bug doesn't trigger.

  3. When built without -g, the test suite's "valgrind output parser" wrongly
     ignored the valgrind output and with libcurl's standard build it is
     typically built without -g. Thus hiding this problem to most users.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2016-9594 to this issue.


This flaw exists in the following libcurl versions.

- Affected versions: libcurl 7.52.0 only
- Not affected versions: libcurl < 7.52.0 and libcurl >= 7.52.1

libcurl is used by many applications, but not always advertised as such!


In version 7.52.1, we fixed the function and we fixed the valgrind parser in
the test suite.

A [patch for CVE-2016-9594]( is


We suggest you take one of the following actions immediately, in order of

  A - Upgrade curl and libcurl to version 7.52.1

  B - Apply the patch to 7.52.0 and rebuild


It was first reported to the curl project on December 21 by Kamil Dudka.

We contacted distros@...nwall on December 21.

curl 7.52.1 was released on December 23 2016, coordinated with the publication
of this advisory.


Reported and patched by Kamil Dudka.



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