[Kimchi-devel] [PATCH] Prevent Kimchi against TLS Logjam attacks

[Rodrigo Trujillo]

There are several weaknesses in how Diffie-Hellman key exchange has been
deployed, allowing a man-in-the-middle attack named Logjam, more details
here: https://weakdh.org.
This patch improves the security in Nginx server, generating 2048bit
DH-Parameters or longer when using 2048bit RSA keys.

Some parameters before patch:
echo | openssl s_client -connect localhost:8001 -cipher "DH"
	Cipher    : DHE-RSA-AES256-GCM-SHA384
	New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-GCM-SHA384
	Server public key is 2048 bit
	Server Temp Key: DH, 1024 bits

Some parameters after patch:
echo | openssl s_client -connect localhost:8001 -cipher "DH"
	Cipher    : DHE-RSA-AES256-GCM-SHA384
	New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-GCM-SHA384
	Server public key is 2048 bit
	Server Temp Key: DH, 2048 bits  (*)

This patch also changes the Ciphers allowed by Nginx, change build
scripts and the RPM spec file to deliver new file: dhparams.pem.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo at linux.vnet.ibm.com>
---
 Makefile.am                   | 1 +
 contrib/kimchi.spec.fedora.in | 3 ++-
 src/Makefile.am               | 8 +++++++-
 src/kimchi/proxy.py           | 6 +++++-
 src/nginx/Makefile.am         | 2 ++
 src/nginx/kimchi.conf.in      | 4 +++-
 6 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/Makefile.am b/Makefile.am
index 46b0b5b..5f2b401 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -133,6 +133,7 @@ install-data-local:
 	touch $(DESTDIR)/var/log/kimchi/kimchi-access.log
 	touch $(DESTDIR)/var/log/kimchi/kimchi-error.log
 	mkdir -p $(DESTDIR)/etc/kimchi/
+	$(INSTALL_DATA) src/nginx/dhparams.pem $(DESTDIR)/etc/kimchi/dhparams.pem
 	touch $(DESTDIR)/etc/nginx/conf.d/kimchi.conf
 
 uninstall-local:
diff --git a/contrib/kimchi.spec.fedora.in b/contrib/kimchi.spec.fedora.in
index dc5533a..de40fd1 100644
--- a/contrib/kimchi.spec.fedora.in
+++ b/contrib/kimchi.spec.fedora.in
@@ -34,6 +34,7 @@ Requires:	python-ldap
 Requires:	python-libguestfs
 Requires:	libguestfs-tools
 BuildRequires:	libxslt
+BuildRequires:	openssl
 BuildRequires:	python-lxml
 
 %if 0%{?rhel} >= 6 || 0%{?fedora} >= 19
@@ -153,7 +154,7 @@ rm -rf $RPM_BUILD_ROOT
 %{_sysconfdir}/kimchi/distros.d/opensuse.json
 %{_sysconfdir}/kimchi/distros.d/ubuntu.json
 %{_sysconfdir}/kimchi/distros.d/gentoo.json
-%{_sysconfdir}/kimchi/
+%{_sysconfdir}/kimchi/*
 %{_sharedstatedir}/kimchi/debugreports/
 %{_sharedstatedir}/kimchi/screenshots/
 %{_sharedstatedir}/kimchi/vnc-tokens/
diff --git a/src/Makefile.am b/src/Makefile.am
index 38d231c..e0e0821 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -45,4 +45,10 @@ kimchid: kimchid.in Makefile
 kimchi.conf: kimchi.conf.in Makefile
 	$(do_substitution) < kimchi.conf.in > kimchi.conf
 
-CLEANFILES = $(bin_SCRIPTS) $(BUILT_SOURCES)
+# Generate unique Diffie-Hellman group with 2048-bit
+all-local: dhparams.pem
+
+dhparams.pem:
+	openssl dhparam -out dhparams.pem 2048
+
+CLEANFILES = $(bin_SCRIPTS) $(BUILT_SOURCES) dhparams.pem
diff --git a/src/kimchi/proxy.py b/src/kimchi/proxy.py
index e3e35b4..5dcca65 100644
--- a/src/kimchi/proxy.py
+++ b/src/kimchi/proxy.py
@@ -68,6 +68,9 @@ def _create_proxy_config(options):
             with open(key, "w") as f:
                 f.write(ssl_gen.key_pem())
 
+    # Setting up Diffie-Hellman group with 2048-bit file
+    dhparams_pem = os.path.join(config_dir, "dhparams.pem")
+
     # Read template file and create a new config file
     # with the specified parameters.
     with open(os.path.join(nginx_config_dir, "kimchi.conf.in")) as template:
@@ -78,7 +81,8 @@ def _create_proxy_config(options):
                                 kimchid_port=options.cherrypy_port,
                                 proxy_ssl_port=options.ssl_port,
                                 cert_pem=cert, cert_key=key,
-                                max_body_size=eval(options.max_body_size))
+                                max_body_size=eval(options.max_body_size),
+                                dhparams_pem=dhparams_pem)
 
     # Write file to be used for nginx.
     config_file = open(os.path.join(nginx_config_dir, "kimchi.conf"), "w")
diff --git a/src/nginx/Makefile.am b/src/nginx/Makefile.am
index 0241b37..c754947 100644
--- a/src/nginx/Makefile.am
+++ b/src/nginx/Makefile.am
@@ -21,3 +21,5 @@ EXTRA_DIST = kimchi.conf.in
 
 confdir = $(sysconfdir)/nginx/conf.d
 dist_conf_DATA = kimchi.conf.in
+
+CLEANFILES = kimchi.conf
diff --git a/src/nginx/kimchi.conf.in b/src/nginx/kimchi.conf.in
index 3ecbde4..b0faea3 100644
--- a/src/nginx/kimchi.conf.in
+++ b/src/nginx/kimchi.conf.in
@@ -53,7 +53,9 @@ http {
         ssl_certificate ${cert_pem};
         ssl_certificate_key ${cert_key};
         ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
-        ssl_ciphers ECDH at STRENGTH:DH at STRENGTH:HIGH:!RC4:!MD5:!DES:!aNULL:!eNULL;
+        ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA:@STRENGTH';
+        ssl_prefer_server_ciphers on;
+        ssl_dhparam ${dhparams_pem};
 
         add_header Strict-Transport-Security "max-age=31536000; includeSubdomains;";
         add_header X-Frame-Options DENY;
-- 
2.1.0