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ReStructuredText
184 lines
6.8 KiB
ReStructuredText
.. _CVE-2021-20288:
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CVE-2021-20288: Unauthorized global_id reuse in cephx
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=====================================================
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* `NIST information page <https://nvd.nist.gov/vuln/detail/CVE-2021-20288>`_
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Summary
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-------
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Ceph was not ensuring that reconnecting/renewing clients were
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presenting an existing ticket when reclaiming their global_id value.
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An attacker that was able to authenticate could claim a global_id in
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use by a different client and potentially disrupt
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other cluster services.
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Background
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----------
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Each authenticated client or daemon in Ceph is assigned a numeric
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global_id identifier. That value is assumed to be unique across the
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cluster. When clients reconnect to the monitor (e.g., due to a
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network disconnection) or renew their ticket, they are supposed to
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present their old ticket to prove prior possession of their global_id
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so that it can be reclaimed and thus remain constant over the lifetime
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of that client instance.
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Ceph was not correctly checking that the old ticket was valid, allowing
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an arbitrary global_id to be reclaimed, even if it was in use by another
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active client in the system.
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Attacker Requirements
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---------------------
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Any potential attacker must:
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* have a valid authentication key for the cluster
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* know or guess the global_id of another client
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* run a modified version of the Ceph client code to reclaim another client's global_id
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* construct appropriate client messages or requests to disrupt service or exploit
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Ceph daemon assumptions about global_id uniqueness
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Impact
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------
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Confidentiality Impact
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______________________
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None
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Integrity Impact
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________________
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Partial. An attacker could potentially exploit assumptions around
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global_id uniqueness to disrupt other clients' access or disrupt
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Ceph daemons.
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Availability Impact
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___________________
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High. An attacker could potentially exploit assumptions around
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global_id uniqueness to disrupt other clients' access or disrupt
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Ceph daemons.
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Access Complexity
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_________________
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High. The client must make use of modified client code in order to
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exploit specific assumptions in the behavior of other Ceph daemons.
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Authentication
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______________
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Yes. The attacker must also be authenticated and have access to the
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same services as a client it is wishing to impersonate or disrupt.
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Gained Access
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_____________
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Partial. An attacker can partially impersonate another client.
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Affected versions
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-----------------
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All prior versions of Ceph monitors fail to ensure that global_id reclaim
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attempts are authentic.
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In addition, all user-space daemons and clients starting from Luminous v12.2.0
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were failing to securely reclaim their global_id following commit a2eb6ae3fb57
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("mon/monclient: hunt for multiple monitor in parallel").
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All versions of the Linux kernel client properly authenticate.
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Fixed versions
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--------------
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* Pacific v16.2.1 (and later)
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* Octopus v15.2.11 (and later)
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* Nautilus v14.2.20 (and later)
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Fix details
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-----------
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#. Patched monitors now properly require that clients securely reclaim
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their global_id when the ``auth_allow_insecure_global_id_reclaim``
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is ``false``. Initially, by default, this option is set to
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``true`` so that existing clients can continue to function without
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disruption until all clients have been upgraded. When this option
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is set to false, then an unpatched client will not be able to reconnect
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to the cluster after an intermittent network disruption breaking
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its connect to a monitor, or be able to renew its authentication
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ticket when it times out (by default, after 72 hours).
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Patched monitors raise the ``AUTH_INSECURE_GLOBAL_ID_RECLAIM_ALLOWED``
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health alert if ``auth_allow_insecure_global_id_reclaim`` is enabled.
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This health alert can be muted with::
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ceph health mute AUTH_INSECURE_GLOBAL_ID_RECLAIM_ALLOWED 1w
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Although it is not recommended, the alert can also be disabled with::
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ceph config set mon mon_warn_on_insecure_global_id_reclaim_allowed false
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#. Patched monitors can disconnect new clients right after they have
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authenticated (forcing them to reconnect and reclaim) in order to
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determine whether they securely reclaim global_ids. This allows
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the cluster and users to discover quickly whether clients would be
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affected by requiring secure global_id reclaim: most clients will
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report an authentication error immediately. This behavior can be
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disabled by setting ``auth_expose_insecure_global_id_reclaim`` to
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``false``::
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ceph config set mon auth_expose_insecure_global_id_reclaim false
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#. Patched monitors will raise the ``AUTH_INSECURE_GLOBAL_ID_RECLAIM`` health
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alert for any clients or daemons that are not securely reclaiming their
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global_id. These clients should be upgraded before disabling the
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``auth_allow_insecure_global_id_reclaim`` option to avoid disrupting
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client access.
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By default (if ``auth_expose_insecure_global_id_reclaim`` has not
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been disabled), clients' failure to securely reclaim global_id will
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immediately be exposed and raise this health alert.
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However, if ``auth_expose_insecure_global_id_reclaim`` has been
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disabled, this alert will not be triggered for a client until it is
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forced to reconnect to a monitor (e.g., due to a network disruption)
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or the client renews its authentication ticket (by default, after
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72 hours).
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#. The default time-to-live (TTL) for authentication tickets has been increased
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from 12 hours to 72 hours. Because we previously were not ensuring that
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a client's prior ticket was valid when reclaiming their global_id, a client
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could tolerate a network outage that lasted longer than the ticket TTL and still
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reclaim its global_id. Once the cluster starts requiring secure global_id reclaim,
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a client that is disconnected for longer than the TTL may fail to reclaim its global_id,
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fail to reauthenticate, and be unable to continue communicating with the cluster
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until it is restarted. The default TTL was increased to minimize the impact of this
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change on users.
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Recommendations
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---------------
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#. Users should upgrade to a patched version of Ceph at their earliest
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convenience.
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#. Users should upgrade any unpatched clients at their earliest
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convenience. By default, these clients can be easily identified by
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checking the ``ceph health detail`` output for the
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``AUTH_INSECURE_GLOBAL_ID_RECLAIM`` alert.
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#. If all clients cannot be upgraded immediately, the health alerts can be
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temporarily muted with::
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ceph health mute AUTH_INSECURE_GLOBAL_ID_RECLAIM 1w # 1 week
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ceph health mute AUTH_INSECURE_GLOBAL_ID_RECLAIM_ALLOWED 1w # 1 week
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#. After all clients have been updated and the ``AUTH_INSECURE_GLOBAL_ID_RECLAIM``
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alert is no longer present, the cluster should be set to prevent insecure
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global_id reclaim with::
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ceph config set mon auth_allow_insecure_global_id_reclaim false
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