libcurl inappropriate GSSAPI delegation
                    =======================================

Project cURL Security Advisory, June 23rd 2011
http://curl.haxx.se/docs/security.html

1. VULNERABILITY

   When doing GSSAPI authentication, libcurl unconditionally performs
   credential delegation. This hands the server a copy of the client's security
   credentials, allowing the server to impersonate the client to any other
   using the same GSSAPI mechanism. This is obviously a very sensitive
   operation, which should only be done when the user explicitly so directs.

   The GSS/Negotiate feature is only used by libcurl for HTTP authentication if
   told to, and only if libcurl was built with a library that provides the
   GSSAPI. Many builds of libcurl don't have GSS enabled.

   There is no known exploit for this problem.

   The Common Vulnerabilities and Exposures (CVE) project has assigned the name
   CVE-2011-2192 to this issue.

2. AFFECTED VERSIONS

   Affected versions: curl 7.10.6 to and including 7.21.6
   Not affected versions: curl < 7.10.6 and >= 7.21.7

   Also note that libcurl is used by many applications, and not always
   advertised as such.

3. THE SOLUTION

   libcurl 7.21.7 avoids setting the option that selects delegation.

4. RECOMMENDATIONS

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

   A - Upgrade to curl and libcurl 7.21.7

   B - Apply this patch and rebuild libcurl

       http://curl.haxx.se/curl-gssapi-delegation.patch

   C - Disable credential forwarding. Assuming the GSSAPI mechanism is
       Kerberos, users can acquire an initial credential (TGT) which is not
       forwardable. On Unix platforms, both the MIT and Heimdal versions of
       kinit use the -F flag for this (note the capital "F"; -f does the
       opposite!). You can also set this as a global default in /etc/krb5.conf
       (or wherever that file lives in a particular installation):

       [libdefaults]
       forwardable = no

   D - Stop using GSS/Negotiate

5. TIME LINE

   Richard Silverman realized the problem exists and reported it to us on June
   6th 2011.

   We discussed solutions and a first patch was written on June 8th.

   curl 7.21.7 was released on June 23rd 2011, coordinated with the publication
   of this this flaw.

6. CREDITS

   Reported to us by Richard Silverman. Thanks a lot!

   Daniel Stenberg wrote the primary patch and this advisory. Additional
   help and valuable feedback provided by Dan Fandrich and Julien Chaffraix.

-- 
  / daniel.haxx.se
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