Shibboleth Developers

["Scott Cantor" <>]

Shibboleth Service Provider Security Advisory [14 December 2004]

Updated versions of the Shibboleth Service Provider software
are now available which correct a security issue:


Insufficient protection against "scope" spoofing
================================================

Shibboleth supports the use of "scoped" attributes, values
which are qualified by a DNS domain-style qualifer that limits
the meaning of the value. Examples include eduPersonScopedAffiliation
and eduPersonPrincipalName from the eduPerson specification.

All versions of the service provider prior to 1.2.1a rely on
the appearance of a Scope attribute in the attribute's XML values
to determine how and whether to apply checks against the scopes
that a given identity provider can assert. This places too much
trust in the identity provider, and prevents a service provider
from enforcing reliable attribute filtering rules based on scope.

In addition, the default value filtering rule supplied for
the eduPersonPrincipalName attribute was too lenient and should
have been used to protect against an attempt to embed a scope
inside the value string improperly.

All versions of Shibboleth prior to 1.2.1a (including the original
1.2.1 bug fix release) are potentially affected by this issue.


Recommendations
---------------

Users running Shibboleth 1.2 can work around the problem and
protect themselves by modifying the AAP.xml file supplied with
the distribution and replacing the <AttributeRule> element
defining the eduPersonPrincipalName attribute, if it is being used,
with the following XML:

====start here====
<AttributeRule Name="urn:mace:dir:attribute-def:eduPersonPrincipalName"
    Header="REMOTE_USER" Alias="user">
    <!-- Basic rule to pass through any legal value. -->
    <AnySite>
        <Value 
Type="regexp">^[^@]+$</Value>
    </AnySite>
</AttributeRule>
====stop here====

The change is the new value filter to block the @ sign from appearing.

When possible, upgrade to the latest patched release of Shibboleth,
1.2.1a.

The patched release contains an enhancement of the AAP plugin
supplied in libexec/xmlproviders.so that allows the AAP.xml
file's <AttributeRule> elements to declare that an attribute must
be scoped, without relying on the identity provider to do the
right thing. It also contains the value filter above, by default.

For users running Windows, a new package and post-install set
for version 1.2.1a has been created and is available at the
download site. New RPMs (1.2.1-2) have also been created for
fedora.

http://wayf.internet2.edu/shibboleth/

The distribution file names are:

    o win32/shibboleth-1.2.1a-win32.exe
      GPG: shibboleth-1.2.1a-win32.exe.asc
      
    o win32/shibboleth-1.2.1-win32-postinstall.zip
      GPG: shibboleth-1.2.1-win32-postinstall.zip.asc

The postinstall archive can be used to replace the updated files
in an installed version. All files updated since the original
release of version 1.2.1 are included. If you have made changes
to your AAP.xml file, you should examine the new file and apply
any changes related to this issue. Be sure to replace the
shibboleth.xsd file as well, or your new configuration will
become invalid.


Credits
-------
Thanks to Ian Young and John Maddock for reporting this problem.

Patches for these issues were created by Scott Cantor,
(),
 the principal developer.


URL for this Security Advisory:
http://shibboleth.internet2.edu/secadv/secadv_20041214.txt