Shared auEduPersonSharedToken (user ID) for all University of Notre Dame Australia users across Australian Access Federation (AAF) Resources

Outline: for an undisclosed period of time until 28 June 2019, all users from The University of Notre Dame Australia (ND) accessing federated, Shibboleth-secured SSO resources provided through the Australian Access Federation (AAF) were issued identical auEduPersonSharedToken values. This identifier is frequently used as a unique user identifier (username); thus for systems where this was the case, all users from ND were considered the same person, causing permission assigned to one user to effectively apply to all members of the ND community, breaking authentication and risking information exposure to sensitive resources. The level of impact on a given system depends on what permissions a given ND user had and how a systme operates – impact could range from disclosure of one account’s details through to complete loss of control and data.

This disclosure is being made in the public interet because at the time of writing (30 May 2020) no-one else has done so.

Introduction

The AAF provides a federated trust network of Identity Providers (IdPs) and Service Providers (SP) between Australia educational institutions, similar to InCommon Federation in the USA and the UK Access Management Federation from Jisc in the UK.

Within any of these types of federation, assurances are given that a user from one organisation will be able to exchange attributes with another in order to allow that user to access some type of service. Whether the user will get access depends on the target SP and its own access controls – it is not guaranteed that just because I have an AAF account I should be able to log into a given system. Services range from web-based platforms utilising Shibboleth SSO to lower-level terminal and network services. As with any trust network, all participants must be trusted to provide accurate user information, as data sent from an IdP on login to an SP will be implicitly trusted when the SAML messages are decrypted and cryptographically verified.

The crux of this issue concerns the auEduPersonSharedToken attribute, which is defined by the AAF as follows:

A unique identifier enabling federation spanning services such as Grid and Repositories. Values of the identifier are generated using a set formula. The value has the following qualities:

  • unique
  • […]
  • not re-assignable

It is these requirements that are the most important in this situation — unique, never reassigned, and unique across the entire federation.

On this page, I look at what happened, the impact of the issue and subsequent processes concerning security and disclosure. Lastly, I discuss suggested improvements to processes and what system administrators may consider doing to detect issues like that in future.

Vulnerability

On the morning of 13 June 2019, I was alerted to a concern from a non-technical system administrator of a portal I operate (“the Portal”) at James Cook University (JCU) where a given user had been able to sign in and access secure resources without seemingly been given access. The reporting party was from ND and had coopted several colleagues to test logging into the Portal and each of them was able to, without fail, obtain full-site level access to all sensitive content on the Portal.

It is at this point, I should clarify the nature of the SSO process of this Portal is such that a user must attempt login into the Portal first so their identity is registered in its account system, and then the system administrator can assign permissions. A user gets no permission by default until granted, and the account system logs the action of logging in.

In this case, looking up one user’s account by name and email address in the Portal yielded a positive result with permissions assigned, but further searches with other colleague names yielded no results. A generic search for @nd.edu.au confusingly yielded just the details of one staff member and subsequent searches would yield a different ND person’s name and email – a seemingly fine example of a heisenbug.

Discussions continued with the Portal’s system administrators and the ND staff members until it was ascertained that the user identifier, auEduPersonSharedToken, was identical between users. The consequence of this is broken authentication, as all ND users would thus present themselves as the same trusted user on the Portal with elevated permissions, and access would continue as this identity permanently as long the ND IdP configuration continued functioning in this manner. When the next ND user logged in, the Portal detected the change in email and common name and diligently updated its own user database – as would happen with a name change say if someone were married or legally changed their name.

For this system, ordinary users were granted a degree of elevated permissions, being able to read and modify all site content, including that belonging to other users. The reaosn for this is that one ND user was a trusted member in the system, thus inadvertently extending that trust to all ND users due to all ND users sharing the same user identity. For other systems, the impact depends on the level of permission granted to any given ND user and the type of system in play – if that ND user was a superuser in a terminal-based application, then any ordinary user could gain root privileges.

At this point, the AAF support were contacted by phone call to seek their responsible disclosure processes and alert them of the impending situation, which was subsequently followed up with an email.

For the Portal, access was revoked to the shared ND user identity immediately and steps were taken across JCU systems with AAF authentication to deny access to all users presenting either that auEduPersonSharedToken or an @nd.edu.au email address until such time as the issue was resolved. All system logs and access control databases across other systems were reviewed for use by ND users; these systems were not designed for ND access, but may have acted as a canary if someone with an ND account was probing systems.

Impact

For the Portal, this resulted in the potential for sensitive data exposure given the nature of the Portal. Logs indicated that the given shared identity did not attempt to access any resources (aside from the homepage) on the system for the duration of logs held, likely attributable to the fact that only one staff member from ND had access to the Portal and knew of its existence.

In general, a vulnerability of this nature could easily be exploited by the fact that University communities are open by design. As all ND users were receiving the same auEduPersonSharedToken, this meant that any student, staff member, alumnus, guest, consultant or technician (see ND Policy Information Security) would be automatically be trusted with the same level of permission and access that the intended ND member has on a given system. To quote their IdP’s description in the AAF metadata.aaf.signed.complete.xml:

IdP for The University of Notre Dame Australia. Available for all staff,
students and alumni to connect to the AAF Federation.

Aside from having the entire University as potential target to locate a single set of credentials, a bad actor could simply sign up as a (potential) student or if physically nearby, perhaps wait until a shared computer was left unattended.

The severity of this issue depends entirely on the target system and how the system is configured, relying on two key points:

  • A given system must have been using auEduPersonSharedToken as its user identifier (compared to the commonly-used eduPersonTargetedID or the often-misused mail attribute), and
  • Someone at ND must have been assigned (or become assigned) a suitable level of elevated access

The comparatively small size of the AAF, ND and Australian higher education communities limits the ability to exploit the issue, but anecdotal indicators from the AAF are that the issue has persisted for an indeterminate amount of time – it is possible that the issue has persisted since 6 July 2016, which is the issue date of the X.509 signing certificate used by idp.nd.edu.au as found in aaf-metadata.xml, assuming that the IdP configuration error wasn’t introduced later.

Resolution

To the credit of the AAF, the initial report was received and acted upon immediately, as explained in the timeline below. Fifteen days later, on 28 June 2019, the AAF reported that the ND had changed and corrected its IdP configuration to assign unique auEduPersonSharedToken identifiers to users. I conducted tests on our system in collaboration with the Portal’s users from ND and subsequently restrictions on ND user accounts were able to be lifted.

A discussion then ensued with the AAF regarding public disclosure of the issue, eventually reaching the point of agreement that disclosure would be provided by ND, sent out to the AAF’s standard Support Notice channels, and seen by all IdPs and SPs. At that point in October 2019, after nearly 4 months, nothing further was heard about the issue until May 2020. Indications are that multiple attempts were made by the AAF to have ND provide the advisory, but none was made and no explanation given as to why.

The final update to date from the AAF has come in 18 May 2020 with a conclusion that getting acknowledgement of this incident from ND is unlikely. The incident has prompted proposed changes in the AAF rules, which consist of the following:

Organisations will be provided a time frame in which to provide an
advisory of issues that may impact of users privacy or security. If no
such advisory is made by the organisation within that time frame the AAF
will send an advisory. [...] All AAF subscribers will be notified of the
changes to the AAF rules after they are passed by the board and members.

Summary

The full extent of this issue remains unknown as no public Security Advisory was or has been made at the time of writing by either The University of Notre Dame Australia or the Australian Access Federation. As mentioned above, the issue may have persisted since July 2016.

For systems under my control that utilise the AAF for login, no suspicious behaviour was identified and the issue was mitigated as soon as it was noticed by system users.

For other services within the AAF, I was notified that logins coming from ND were being reviewed and contact was being made with any other affected organisations or systems.

This issue highlights the need for better testing, review processes and validating attributes being shared from IdPs within the AAF. A process of validation should test attributes, ideally automatically, according to their Federation rules. In the case of attributes which may be used as user identifiers, tests must ensure those attributes are unique across multiple or all users at an organisation, and in the case of the auEduPersonSharedToken unique across all users in the Federation. How this might be achieved must also ensure user privacy is maintained.

The issue also highlights the need for better communication and security disclosure processes from Australian higher education institutions, particularly within those participating as members within the Australian Access Federation. The proposed changes to AAF rules as at 18 May 2020 to improve processes for future Security Advisories within the AAF are welcome and should address these concerns.

Regardless of rule changes, future systems that utilise federated login should consider implementing an alert system to detect and report on significant or complete attribute replacement for a given user, and consider detecting use of multiple logins with the same identifier from different IPs or locations, even when using a trusted set of attributes, delivered from the AAF or any similar federation.

Disclosure Timeline

  • 2019-06-13: Discovery by system administrators of an AAF-secured system; all access to this and other federated systems revoked for ND users
  • 2019-06-13 11:53 AEST: Responsible disclosure made to AAF Support
  • 2019-06-13 14:16 AEST: Acknowledgement from AAF that identity management team at Notre Dame had been contacted and were waiting a response
  • 2019-06-13 15:19 AEST: Response from AAF that issue at ND was identified; at this point, all users from ND were being assigned the same value for auEduPersonSharedToken
  • 2019-06-28: Notification from AAF that ND had modified their IdP configuration to ensure unique auEduPersonSharedToken values were issued for all of their users
  • 2019-06-28: Request made to AAF as to what disclosure would occur, to whom and when; response from AAF that they were discussing this topic with ND; further request made to the AAF regarding a public advisory of the security issue
  • 2019-07-03: Response from AAF that AAF is organising a conversation with the ND ISO and CIO to ask them to notify identified service providers about the issue; AAF intended to to communicate a Security Incident advisory to IdP operators
  • 2019-07-03: Reiteration of request made to the AAF regarding a public advisory of the security issue; response from AAF that the IdP Security Incident Advisory would be published on Support notices page and sent via email to support notice recipients, equating to all IdPs and SPs being slated to see the message from the AAF
  • 2019-10-10: Follow up sent to AAF regarding the status fo the security advisory as one had not yet been seen
  • 2019-10-11: Response from AAF that they were working with ND to have them provide the advisory and that was the source of the delay
  • 2019-10-11: Request made to AAF as to an ETA for the Security Advisory; response received that no ETA existed at that time
  • 2020-05-18: Notification from AAF that the chances of Notre Dame publicly acknowledging the incident were very mote, given multiple attempts from the AAF. AAF Board has planned a change to AAF rules addressing future occurrences and all AAF subscribers will apparently be notified of the changes to AAF rules once passed by the board and members. Original security issue logged with AAF was closed.
  • 2020-05-30: Public disclosure on this page
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