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AUSCERT External Security Bulletin Redistribution
ESB-2020.1359
openvpn -- illegal client float can break VPN session for other users
17 April 2020
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AusCERT Security Bulletin Summary
---------------------------------
Product: openvpn
Publisher: FreeBSD
Operating System: FreeBSD
UNIX variants (UNIX, Linux, OSX)
Impact/Access: Denial of Service -- Remote with User Interaction
Resolution: Patch/Upgrade
CVE Names: CVE-2020-11810
Original Bulletin:
http://www.vuxml.org/freebsd/8604121c-7fc2-11ea-bcac-7781e90b0c8f.html
Comment: This advisory references vulnerabilities in products which run on
platforms other than FreeBSD. It is recommended that administrators
running openvpn check for an updated version of the software for
their operating system.
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openvpn -- illegal client float can break VPN session for other users
Affected packages
openvpn < 2.4.8_3
openvpn-mbedtls < 2.4.8_3
openvpn-devel < 202016
Details
VuXML ID 8604121c-7fc2-11ea-bcac-7781e90b0c8f
Discovery 2020-04-13
Entry 2020-04-16
Lev Stipakov and Gert Doering report:
There is a time frame between allocating peer-id and initializing data
channel key (which is performed on receiving push request or on async
push-reply) in which the existing peer-id float checks do not work right.
If a "rogue" data channel packet arrives during that time frame from
another address and with same peer-id, this would cause client to float to
that new address.
The net effect of this behaviour is that the VPN session for the "victim
client" is broken. Since the "attacker client" does not have suitable keys,
it can not inject or steal VPN traffic from the other session. The time
window is small and it can not be used to attack a specific client's
session, unless some other way is found to make it disconnect and reconnect
first.
[source]
References
CVE CVE-2020-11810
URL https://community.openvpn.net/openvpn/ticket/1272
URL https://github.com/OpenVPN/openvpn/commit/
f7b318f811bb43c0d3aa7f337ec6242ed2c33881
URL https://patchwork.openvpn.net/patch/1077/
URL https://sourceforge.net/p/openvpn/openvpn/ci/
f7b318f811bb43c0d3aa7f337ec6242ed2c33881/
URL https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/
msg19720.html
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