Summary
-------
An incorrect implementation of XEP-0280: Message Carbons[0] in multiple
XMPP clients allows a remote attacker to impersonate any user, including
contacts, in the vulnerable application's display. This allows for
various kinds of social engineering attacks.
Classification
--------------
- CWE-304: Missing Critical Step in Authentication
- CWE-940: Improper Verification of Source of a Communication Channel
- CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N (score 7.1)
Affected Applications
---------------------
- CVE-2017-5589: yaxim and Bruno (0.8.6 - 0.8.8; Android)
- CVE-2017-5590: ChatSecure (3.2.0 - 4.0.0; only iOS) and Zom (all versions up to 1.0.11; only iOS)
- CVE-2017-5591: poezio (0.8 - 0.10)
- CVE-2017-5592: profanity (0.4.7 - 0.5.0)
- CVE-2017-5593: Psi+ (0.16.563.580 - 0.16.571.627)
- CVE-2017-5602: jappix (1.0.0 to 1.1.6)
- CVE-2017-5603: Jitsi (2.5.5061 - 2.9.5544)
- CVE-2017-5604: mcabber (1.0.0 - 1.0.4)
- CVE-2017-5605: Movim (0.8 - 0.10)
- CVE-2017-5606: Xabber (only if manually enabled: 1.0.30, 1.0.30 VIP, beta 1.0.3 - 1.0.74; Android)
- CVE-2017-5858: Converse.js (0.8.0 - 1.0.6, 2.0.0 - 2.0.4)
Affected Libraries
------------------
- CVE-2017-5591: SleekXMPP unknown up to 1.3.1
- CVE-2017-5591: Slixmpp all versions up to 1.2.3
Details
-------
The XMPP protocol extension "XEP-0280: Message Carbons"[0] allows
a user to run multiple clients on their XMPP account by sending "carbon
copies" of outgoing and incoming messages to the user's other devices
(besides the one that directly sent or received the original message).
This feature must be supported by the user's server and must be
explicitly enabled by the client. Carbon copies are always generated by
the user's server and originate from the user's bare JID (their account
address).
For example, the following is message "Hi!", sent by Alice
(`alice@xmpp.example`) to Bob's client 1 (`bob@xmpp.example/client1`):
<message from="alice@xmpp.example" to="bob@xmpp.example/client1">
<body>Hi!</body>
</message>
Bob is also logged in with carbons-enabled client 2, which receives the
following carbon-copy of the message:
<message from="bob@xmpp.example" to="bob@xmpp.example/client2">
<received xmlns='urn:xmpp:carbons:2'><forwarded xmlns='urn:xmpp:forward:0'>
<message from="alice@xmpp.example" to="bob@xmpp.example/client1">
<body>Hi!</body>
</message>
</forwarded></received>
</message>
Now, client 2 can extract the original message from the carbon copy and
display it accordingly. The "Security Considerations" section of
XEP-0280 explicitly states that:
| Any forwarded copies received by a Carbons-enabled client MUST be from
| that user's bare JID; any copies that do not meet this requirement
| MUST be ignored.
The Carbons implementation in the affected clients was lacking this
test. It simply checked all incoming messages for presence of a Carbon
element (`<received/>` or `<sent/>`), extracted and parsed it like a
regular message.
Therefore, it was possible for Mallory to send the following specially
crafted message to Bob:
<message from="mallory@evil.example" to="b@xmpp.example">
<received xmlns='urn:xmpp:carbons:2'><forwarded xmlns='urn:xmpp:forward:0'>
<message from="alice@xmpp.example" to="bob@xmpp.example/client1">
<body>Please come to Creepy Valley tonight, alone!</body>
</message>
</forwarded></received>
</message>
This would appear as an authentic message from Alice, including Alice'
proper screen name, allowing Mallory to perform social engineering
attacks on Bob.
Mitigation
----------
While the attacker can send messages in the name of somebody else, they
can not see your responses. Therefore, if you receive a phony message
while using an affected client, reinsure with the message sender by
either challenging them with a question that can not be guessed by the
attacker, or by using out-of-band means.
Xabber: disable the experimental Carbons feature in the app settings.
yaxim: Disabling Message Carbons under "Settings" / "Edit account" /
"Message Carbons (XEP-0280)" will not solve the problem, as the
malicious messages still will be interpreted.
Timeline
--------
- 2017-01-20 Discovery of vulnerability
- 2017-01-23 - 26 Notification of developers
- 2017-01-25 Release of ChatSecure 4.0.1
fix commit:
https://github.com/ChatSecure/ChatSecure-iOS/commit/a340b4bb519227d89f85f2716a10a197a65d4856
- 2017-01-26 Release of jappix 1.1.7
fix commit:
https://github.com/jappix/jappix/commit/ea6de7c65b80880bdf85df47c1a8a5d3d68491af
- 2017-01-28 Release of Psi+ 0.16.571.630
fix commit:
https://github.com/psi-im/iris/pull/47/commits/02e976d4426a1319a7af7d26d7aba9d8c6077570
- 2017-01-29 Release of profanity 0.5.1
fix commit:
https://github.com/boothj5/profanity/commit/8e75437a7e43d4c55e861691f74892e666e29b0b
- 2017-01-29 Release of mcabber 1.0.5
fix commit: https://mcabber.com/hg/rev/2a9569fd7644
- 2017-01-30 Release of poezio 0.11 with slixmpp 1.2.4
slixmpp fix commit:
https://github.com/poezio/slixmpp/commit/22664ee7b86c8e010f312b66d12590fb47160ad8
- 2017-01-31 Release of yaxim and Bruno 0.9.0
fix commit:
https://github.com/ge0rg/yaxim/commit/65a38dc77545d9568732189e86089390f0ceaf9f
- 2017-01-31 Release of Movim 0.11alpha1
fix commit:
https://github.com/movim/moxl/commit/838b0a42efc3b67cc17d63e25ae1d0ea849cd89b
- 2017-01-31 Notification of Debian Security Team
- 2017-02-01 Release of profanity 0.4.7.patch1 and 0.5.0.patch1 (backports of the fix)
- 2017-02-01 Release of Converse.js 1.07 and 2.05
fix commit:
https://github.com/jcbrand/converse.js/commit/42f249cabbbf5c026398e6d3b350f6f9536ea572
- 2017-02-05 Release of Jitsi 2.10
fix commit:
https://github.com/jitsi/jitsi/commit/7d66da61b316c9480b63000f831b6de723b87315
- 2017-02-08 Release of Zom 1.0.12
fix commit:
https://github.com/zom/Zom-iOS/commit/880051eaa8ba32d1b257c87a7d8798a93561bfd3
- 2017-02-09 Publication of this advisory
Acknowledgements
----------------
- Daniel Gultsch for CVE-2015-8688: Gajim Roster Push Attack / Message
Interception[1]
- Sam Whited for CVE-2016-9928 (same as above in mcabber)[2]
- Thijs Alkemade for being an awesome XMPP security researcher (and
for proof-reading this)[3]
Links
-----
[0] https://xmpp.org/extensions/xep-0280.html
[1] https://gultsch.de/gajim_roster_push_and_message_interception.html
[2] http://www.openwall.com/lists/oss-security/2016/12/09/5
[3] https://blog.thijsalkema.de/
HTML version of advisory:
https://rt-solutions.de/en/2017/02/CVE-2017-5589_xmpp_carbons/
PDF version of advisory:
https://rt-solutions.de/wp-content/uploads/2017/02/CVE-2017-5589_xmpp_carbons.pdf
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Dr.-Ing. Georg Lukas
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