[keycloak-user] SAML Advice assertion with signature

Thu Jul 5 02:32:23 EDT 2018

Hi Sebastian,

Nice to meet again! ;) Everything well, here! How’s life over there?

Wrt our issue: currently we managed to get the X.509’s of the missing signatures so the issue is (fortunately) less urgent. 

We are using a custom extension to the SAML provider to support eHerkenning since KeyCloak seems to make some assumptions that do not hold (e.g. entityId is based on the uri). I’ll try to make some time in the next weeks to see if I can offer some patches in this area, or if we can share the eHerkenning stuff in some other way as well. 

(FYI: eHerkenning is a Dutch company identification provider and is part of the European eIDAS scheme. May thus be interesting to support out of the box for Keycloak.)

Kind regards,
Arjan 

> On 04-07-2018, at 13:40, Sebastian Laskawiec <slaskawi at redhat.com> wrote:
> 
> Hey Arjan,
> 
> Long time no see! I hope you're well!
> 
> More comment inlined.
> 
> Thanks,
> Sebastian
> 
> On Thu, Jun 28, 2018 at 4:53 PM Arjan Lamers <a.lamers at first8.nl <mailto:a.lamers at first8.nl>> wrote:
> Hi,
> 
> We are running KeyCloak 3.4.3-Final for a client  and are running into trouble with an identity provider (the dutch eHerkenning) that is using SAML Advice tags.
> 
> We were running an older version of KeyCloak and recently that identity provider started to use <saml:Advice> tags in their responses. We found https://issues.jboss.org/browse/KEYCLOAK-5644 <https://issues.jboss.org/browse/KEYCLOAK-5644>, adding support for the Advice tag and that made us upgrade to 3.4.3. However, this patch does not seem to be complete.
> 
> The patch there ignores the Advice tag when parsing the document. This is fine. However, in our case, the Advice contains two Assertions, both of which are signed (have a Signature tag). The document verification seems to also validate these signatures. This is a problem, since we do not have the keys for these advices, hence the validation fails. 
> 
> We have been advised to fully ignore the Advice tag, including the underlying signatures. I am not a SAML expert but that feels a bit wrong. Any thoughts on that?
> 
> Perhaps Hynek or Stian could correct me here but the spec says the `Advice` elements can be completely ignored:
> 
> "The <Advice> element contains any additional information that the SAML authority wishes to provide.
> This information MAY be ignored by applications without affecting either the semantics or the validity of
> the assertion."
> 
> [1] Page 26 https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf <https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf>
>  
> 
> However, if we do want to go down this road, we would probably patch this in
>          org.keycloak.saml.processing.core.util.XMLSignatureUtil.validate(Document signedDoc, final KeyLocator locator)
> by skipping over nodes that have an ‘Advice’ parent. 
> 
> This situation seems to be very tricky here. Looking through the spec I found that `Advice` tags need to be validated using lax XML validation (just as a reminder, lax validation doesn't fail if the schema is not found) [2]:
> 
> "<Advice> and AdviceType: In addition to SAML-native elements, allows elements from other
> namespaces with lax schema validation processing."
> 
> There's also a note on signature verification [3]:
> 
> "The SAML assertion MAY be signed, which provides both
> authentication of the issuer and integrity protection.
> If such a signature is used, then the <ds:Signature> element MUST be present, and a relying party
> MUST verify that the signature is valid (that is, that the assertion has not been tampered with) in
> accordance with [XMLSig]. If it is invalid, then the relying party MUST NOT rely on the contents of the
> assertion. If it is valid, then the relying party SHOULD evaluate the signature to determine the identity and
> appropriateness of the issuer and may continue to process the assertion in accordance with this
> specification and as it deems appropriate (for example, evaluating conditions, advice, following profile specific
> rules, and so on)."
> 
> So to sum it up:
> Advice tag can be ignored completely
> Advice tag needs only lax validation, so it just needs to be a well formed XML, and that's basically it.
> If a verifier finds a signature, it needs to validate it. If the signature doesn't pass the validation, we can not rely on the assertion.
> From this point, I guess patching the SignatureUtil to skip verification of signatures located in `Advice` element, seems not to violate anything. That's what we should do in my opinion.
> 
> [2] Page 75 https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf <https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf>
> [3] Page 16 https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf <https://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf>
>  
> 
> Would that be an appropriate approach? Would you be interested in such a patch?
> 
> Yes, definitely! Let's start with a patch for master branch and later on, we could cherry-pick it to 3.x if needed.
>  
> 
> 
> Met vriendelijke groet,
> 
> Arjan Lamers
> Software Architect
> +31 (0)6 23 82 24 05
> 
> 
> 
> a.lamers at first8.nl <mailto:a.lamers at first8.nl>
> https://www.first8.nl <https://www.first8.nl/> <http://www.first8.nl/ <http://www.first8.nl/>>
> Linkedin https://www.linkedin.com/in/arjanl <https://www.linkedin.com/in/arjanl> <https://www.linkedin.com/in/profiel-id <https://www.linkedin.com/in/profiel-id>>
> Kerkenbos 1059b
> 6546 BB Nijmegen
> 
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> 
> 
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Met vriendelijke groet,

Arjan Lamers
Software Architect
+31 (0)6 23 82 24 05

a.lamers at first8.nl
https://www.first8.nl <http://www.first8.nl/>
Linkedin https://www.linkedin.com/in/arjanl <https://www.linkedin.com/in/profiel-id>
Kerkenbos 1059b
6546 BB Nijmegen

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