Security Advisory June 23 2011
libcurl inappropriate GSSAPI delegation
Project cURL Security Advisory, June 23rd 2011
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.
We suggest you take one of the following actions immediately, in order of
A - Upgrade to curl and libcurl 7.21.7
B - Apply this patch and rebuild libcurl
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):
forwardable = no
D - Stop using GSS/Negotiate
5. TIME LINE
Richard Silverman realized the problem exists and reported it to us on June
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.
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.