From: Steffan Karger Date: Sun, 3 Jun 2018 12:11:56 +0200 Message-Id: <1528020718-12721-1-git-send-email-steffan@...1856...> Subject: [Openvpn-devel] [PATCH 1/3] man: add security considerations to --compress section List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: openvpn-devel@lists.sourceforge.net As Ahamed Nafeez reported to the OpenVPN security team, we did not sufficiently inform our users about the risks of combining encryption and compression. This patch adds a "Security Considerations" paragraph to the --compress section of the manpage to point the risks out to our users. Signed-off-by: Steffan Karger --- doc/openvpn.8 | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/doc/openvpn.8 b/doc/openvpn.8 index 4114f40..0e5d467 100644 --- a/doc/openvpn.8 +++ b/doc/openvpn.8 @@ -2516,6 +2516,16 @@ If the parameter is empty, compression will be turned off, but the packet framing for compression will still be enabled, allowing a different setting to be pushed later. + +.B Security Considerations + +Compression and encryption is a tricky combination. If an attacker knows or is +able to control (parts of) the plaintext of packets that contain secrets, the +attacker might be able to extract the secret if compression is enabled. See +e.g. the CRIME and BREACH attacks on TLS which also leverage compression to +break encryption. If you are not entirely sure that the above does not apply +to your traffic, you are advised to *not* enable compression. + .\"********************************************************* .TP .B \-\-comp\-lzo [mode] -- 2.7.4