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Date: Tue, 17 Nov 2020 09:10:00 -0500
From: Ana McTaggart <>
To: Ilya Dryomov <>,
Subject: CVE-2020-25677 ceph: CEPHX_V2 replay attack protection lost

Dear all,
cephx authentication protocol does not verify ceph clients correctly, and
is vulnerable to replay attacks in nautilus and later. An attacker with
access to the Ceph cluster network can use this vulnerability to
authenticate with ceph service, via a packet sniffer. This allows them to
perform actions allowed by the ceph service. This is a reintroduction of
CVE-2018-1128[1], affecting msgr2 protocol. msgr 2 protocol is used for all
communication except for older clients that do not support msgr2 protocol.
msgr1 protocol is not affected.

This was introduced in commit to msgr2 321548010578 ("mon/MonClient: skip
CEPHX_V2 challenge if client doesn't support it") , due to commit
c58c5754dfd2 ("msg/async/ProtocolV1: use AuthServer and AuthClient") . This
results in nautilus and ceph being affected because commit c58c5754dfd2
wasn't backported to nautilus, and although msgr1 isn't affected in
nautilus, msgr 2 is the default. This made it so authorizer challenges
could be skipped for peers which did not support CEPHX_V2, unfortunately
making it so authorizer challenges are skipped for all peers in both msgr 1
and msgr2 cases, disabling the protection that was put in place in commit
f80b848d3f83 ("auth/cephx: add authorizer challenge", CVE-2018-1128).

Proposed Patch:
See attached.

We have assigned it a CVE of CVE-2020-25677 at Red Hat.

Credits to Ilya Dryomov


Ana McTaggart

Red Hat Product Security

Red Hat Remote <> for urgent response

M: 7742790791     IM: amctagga


Content of type "text/html" skipped

Download attachment "0003-mon-MonClient-bring-back-CEPHX_V2-authorizer-challen.patch" of type "application/x-patch" (3959 bytes)

Download attachment "0001-msg-async-ProtocolV1-resurrect-include-MGR-as-servic.patch" of type "application/x-patch" (1505 bytes)

Download attachment "0002-msg-async-ProtocolV1-resurrect-implement-cephx_-requ.patch" of type "application/x-patch" (2918 bytes)

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