OpenSAML-C++ / Service Provider Security Advisory [13 March 2025]

[Cantor, Scott]

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Shibboleth Service Provider Security Advisory [13 March 2025]
OpenSAML-C++ Security Advisory [13 March 2025]

An updated version of the OpenSAML C++ library is available
which corrects a parameter manipulation vulnerability when
using SAML bindings that rely on non-XML signatures.

The Shibboleth Service Provider is impacted by this issue, and
it manifests as a critical security issue in that context.

Parameter manipulation allows the forging of signed SAML messages
=================================================================
A number of vulnerabilities in the OpenSAML library used by the
Shibboleth Service Provider allowed for creative manipulation of
parameters combined with reuse of the contents of older requests
to fool the library's signature verification of non-XML based
signed messages.

Most uses of that feature involve very low or low impact use cases
without critical security implications; however, there are two
scenarios that are much more critical, one affecting the SP and
one affecting some implementers who have implemented their own
code on top of our OpenSAML library and done so improperly.

The SP's support for the HTTP-POST-SimpleSign SAML binding for
Single Sign-On responses is its critical vulnerability, and
it is enabled by default (regardless of what one's published
SAML metadata may advertise).

The other critical case involves a mistake that does *not*
impact the Shibboleth SP, allowing SSO to occur over the
HTTP-Redirect binding contrary to the plain language of the
SAML Browser SSO profile. The SP does not support this, but
other implementers may have done so.

Recommendations
===============
Update to V3.3.1 (or later) of the OpenSAML library package.

On non-Windows platforms this is sufficient to address the issue
with a subsequent restart of the SP's "shibd" daemon to pick up
the change.

On Windows, the Service Provider V3.5.0.1 (or later) installer
contains the updated OpenSAML DLL and must be applied to obtain
the fix.

In all cases, the "shibd" log file will log the library versions
in use and the OpenSAML version should be at least 3.3.1 to
indicate the fix is applied.

Prior to updating, it is possible to mitigate the POST-SimpleSign
vulnerability by editing the protocols.xml configuration file and
removing this line:

<Binding id="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST-SimpleSign"
	path="/SAML2/POST-SimpleSign" />

Note that this does not mitigate all aspects of the vulnerability
but it does address the critical one.

Legacy SP configurations with very old per-handler configurations
may include a reference to an AssertionConsumerService handler
supporting this binding and that can be removed as a mitigation
in such cases.

Credits
=======
Thanks to Alexander Tan of SecureSAML for discovering and reporting
this vulnerability, and reviewing the changes.


URL for this Security Advisory:
https://shibboleth.net/community/advisories/secadv_20250313.txt

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