From: Phil Pennock <pdp@exim.org>
Date: Sun, 6 May 2012 09:50:57 +0000 (-0700)
Subject: Disable SSLv2 by default.
X-Git-Tag: exim-4_80_RC7^2
X-Git-Url: https://git.exim.org/users/heiko/exim.git/commitdiff_plain/refs/remotes/pdp/openssl_disable_ssl2

Disable SSLv2 by default.
---

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index c4739a80f..a00908fe4 100644
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -14355,7 +14355,7 @@ harm. This option overrides the &%pipe_as_creator%& option of the &(pipe)&
 transport driver.
 
 
-.option openssl_options main "string list" unset
+.option openssl_options main "string list" "+no_sslv2"
 .cindex "OpenSSL "compatibility options"
 This option allows an administrator to adjust the SSL options applied
 by OpenSSL to connections.  It is given as a space-separated list of items,
diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index ed226b756..6b2b62cdb 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -86,6 +86,8 @@ PP/19 DNS resolver init changes for NetBSD compatibility.  (Risk of breakage
       Not seeing resolver debug output on NetBSD, but suspect this is a
       resolver implementation change.
 
+PP/20 Disable SSLv2 by default in OpenSSL support.
+
 
 Exim version 4.77
 -----------------
diff --git a/doc/doc-txt/NewStuff b/doc/doc-txt/NewStuff
index 2872d241f..6eae4ce7b 100644
--- a/doc/doc-txt/NewStuff
+++ b/doc/doc-txt/NewStuff
@@ -56,6 +56,10 @@ Version 4.78
 
     Currently OpenSSL only.
 
+ 8. SSLv2 now disabled by default in OpenSSL.  (Never supported by GnuTLS).
+    Use "openssl_options -no_sslv2" to re-enable support, if your OpenSSL
+    install was not built with OPENSSL_NO_SSL2 ("no-ssl2").
+
 
 Version 4.77
 ------------
diff --git a/doc/doc-txt/OptionLists.txt b/doc/doc-txt/OptionLists.txt
index 52a24b198..d6fedcb5c 100644
--- a/doc/doc-txt/OptionLists.txt
+++ b/doc/doc-txt/OptionLists.txt
@@ -373,7 +373,7 @@ once                                 string*         unset         autoreply
 once_file_size                       integer         0             autoreply         3.20
 once_repeat                          time            0s            autoreply         2.95
 one_time                             boolean         false         redirect          4.00
-openssl_options                      string          unset         main              4.73 default to unset in 4.78
+openssl_options                      string          +no_sslv2     main              4.73 default changed in 4.78
 optional                             boolean         false         iplookup          4.00
 oracle_servers                       string          unset         main              4.00
 owners                               string list     unset         redirect          4.00
diff --git a/src/README.UPDATING b/src/README.UPDATING
index 5b6bea869..12335eab8 100644
--- a/src/README.UPDATING
+++ b/src/README.UPDATING
@@ -39,6 +39,12 @@ Exim version 4.78
    the message.  No tool has been provided as we believe this is a rare
    occurence.
 
+ * For OpenSSL, SSLv2 is now disabled by default.  (GnuTLS does not support
+   SSLv2).  RFC 6176 prohibits SSLv2 and some informal surveys suggest no
+   actual usage.  You can re-enable with the "openssl_options" Exim option,
+   in the main configuration section.  Note that supporting SSLv2 exposes
+   you to ciphersuite downgrade attacks.
+
  * With OpenSSL 1.0.1+, Exim now supports TLS 1.1 and TLS 1.2.  If built
    against 1.0.1a then you will get a warning message and the
    "openssl_options" value will not parse "no_tlsv1_1": the value changes
@@ -48,8 +54,9 @@ Exim version 4.78
    "openssl_options" gains "no_tlsv1_1", "no_tlsv1_2" and "no_compression".
 
    COMPATIBILITY WARNING: The default value of "openssl_options" is no longer
-   "+dont_insert_empty_fragments".  We default to unset.  That old default was
-   grandfathered in from before openssl_options became a configuration option.
+   "+dont_insert_empty_fragments".  We default to "+no_sslv2".
+   That old default was grandfathered in from before openssl_options became a
+   configuration option.
    Empty fragments are inserted by default through TLS1.0, to partially defend
    against certain attacks; TLS1.1+ change the protocol so that this is not
    needed.  The DIEF SSL option was required for some old releases of mail
diff --git a/src/src/tls-openssl.c b/src/src/tls-openssl.c
index e609670ee..ea32bdb40 100644
--- a/src/src/tls-openssl.c
+++ b/src/src/tls-openssl.c
@@ -481,7 +481,13 @@ list of available digests. */
 EVP_add_digest(EVP_sha256());
 #endif
 
-/* Create a context */
+/* Create a context.
+The OpenSSL docs in 1.0.1b have not been updated to clarify TLS variant
+negotiation in the different methods; as far as I can tell, the only
+*_{server,client}_method which allows negotiation is SSLv23, which exists even
+when OpenSSL is built without SSLv2 support.
+By disabling with openssl_options, we can let admins re-enable with the
+existing knob. */
 
 ctx = SSL_CTX_new((host == NULL)?
   SSLv23_server_method() : SSLv23_client_method());
@@ -1522,6 +1528,9 @@ BOOL adding, item_parsed;
 result = 0L;
 /* Prior to 4.78 we or'd in SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS; removed
  * from default because it increases BEAST susceptibility. */
+#ifdef SSL_OP_NO_SSLv2
+result |= SSL_OP_NO_SSLv2;
+#endif
 
 if (option_spec == NULL)
   {