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Shibboleth Identity Provider Plugin Security Advisory [9 November 2026]

An updated version of the OpenID Connect OP plugin for the Shibboleth
Identity Provider is now available which corrects a deficiency in the
use of DPoP proof within PAR requests.

This issue is considered of "low" security importance to deployments,
and most deployments likely do not make use of this feature.

OpenID Connect OP plugin does not bind the DPoP proof in PAR requests
======================================================================
The OAuth 2.0 Demonstrating Proof of Possession (DPoP) specification [1]
specifies two methods for binding the authorization code to a DPoP key
when Pushed Authorization Requests (PARs) [2] are used in conjunction
with DPoP: the request parameter (dpop_jkt) and the use of DPoP proof
included in the PAR request. Both of these methods must be supported
by authorization servers that support both PAR and DPoP.

The OP plugin properly supported only the first method. When a client
sent a PAR request with DPoP proof, the OP plugin correctly verified
the proof but did not bind the public key thumbprint to the later
stages of the sequence. This means that another DPoP key could be
successfully used in the token endpoint request with the authorization
code that was obtained from the authorize endpoint via PAR-produced
request URI.

If an attacker was somehow able to obtain the authorization code, the
attacker could fetch an access token bound to a new key, or possibly no
key if allowed by configuration. In order to do that, the attacker would
still need to be able to access the token endpoint on the client's
behalf: for confidential clients the client credentials would be needed
and the PKCE code verifier is needed for any clients that used PKCE.

Recommendations
===============
Update to V4.3.3 or later of the OIDC OP plugin, which is now available.
The IdP's plugin installer can perform this update process.

Versions of the OIDC OP plugin from 4.2.0 through 4.3.2 are affected.

Credits
=======
Janne Lauros, CSC - IT Center for Science Ltd

[1] https://datatracker.ietf.org/doc/html/rfc9449
[2] https://datatracker.ietf.org/doc/html/rfc9126

URL for this Security Advisory:
https://shibboleth.net/community/advisories/secadv_20261109a.txt
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