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

Last updated on [18 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. V3.5.0.2 corrects a mistake in one log line that failed
to report the proper library version but is otherwise the same
code as V3.5.0.1.

The "shibd" log file will log the library versions n use and the
OpenSAML version should be at least 3.3.1 to indicate the fix is
applied.

Contrary to the initial publication of this advisory, there is no
workaround within the SP configuration other than to remove the
"SimpleSigning" security policy rule from the security-policy.xml
file entirely.

That will also prevent support of legitimate signed requests or
responses via the HTTP-Redirect binding, which is generally used
only for logout messages within the SP itself. Maintaining support
for logout while applying the mitigation to the SP is possible by
removing the HTTP-Redirect binding from an SP's metadata so that
IdP(s) will select the HTTP-POST binding (using XML-based signatures)
in its place.

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

History
=======
2025-03-14 - remove the mention of original ineffective workaround.
2025-03-17 - clarify the end of the mitigation section and a mistake
in one of the log lines mentioned.
2025-03-18 - remove log line mention after uploading fixed installer

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