From 5d5233778868ddd568140c394adfcfc8e3453245 Mon Sep 17 00:00:00 2001 From: Steffan Karger Date: Sun, 15 Feb 2015 15:24:26 +0100 Subject: Disable SSL compression As reported in trac #502, SSL compression can cause problems in some corner cases. OpenVPN does not need SSL compression, since the control channel is low bandwidth. This does not influence the data channel compressen (i.e. --comp or --comp-lzo). Even though this has not yet been relevant for OpenVPN (since an attacker can not easily control contents of control channel messages), SSL compression has been used in the CRIME and BREACH attacks on TLS. TLS 1.3 will probably even remove support for compression all together, for exactly this reason. Since we don't need it, and SSL compression causes issues, let's just disable it in OpenSSL builds. PolarSSL has no run-time flag to disable compression, but is by default compiled without compression. Signed-off-by: Steffan Karger Acked-by: Arne Schwabe Acked-by: Gert Doering Message-Id: <1424010266-5910-1-git-send-email-steffan@karger.me> URL: http://article.gmane.org/gmane.network.openvpn.devel/9453 Signed-off-by: Gert Doering --- src/openvpn/ssl_openssl.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'src') diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c index 48c0571..d9abc6e 100644 --- a/src/openvpn/ssl_openssl.c +++ b/src/openvpn/ssl_openssl.c @@ -202,6 +202,10 @@ tls_ctx_set_options (struct tls_root_ctx *ctx, unsigned int ssl_flags) #ifdef SSL_OP_NO_TLSv1_2 if (tls_ver_min > TLS_VER_1_2 || tls_ver_max < TLS_VER_1_2) sslopt |= SSL_OP_NO_TLSv1_2; +#endif +#ifdef SSL_OP_NO_COMPRESSION + /* Disable compression - flag not available in OpenSSL 0.9.8 */ + sslopt |= SSL_OP_NO_COMPRESSION; #endif SSL_CTX_set_options (ctx->ctx, sslopt); } -- cgit