Reject vulnerable keys to mitigate Debian OpenSSL flaw

In 2008, Debian (and derived distributions such as Ubuntu) shipped an
OpenSSL package with a flawed random number generator, causing OpenSSH to
generate only a very limited set of keys which were subject to private half
precomputation.  To mitigate this, this patch checks key authentications
against a blacklist of known-vulnerable keys, and adds a new ssh-vulnkey
program which can be used to explicitly check keys against that blacklist.
See CVE-2008-0166.

Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1469
Last-Update: 2013-09-14

Patch-Name: ssh-vulnkey.patch

1 files changed, 9 insertions, 0 deletions

diff --git a/readconf.c b/readconf.c
index 2695fd6c0..22e5a3a61 100644
--- a/readconf.c
+++ b/readconf.c
@@ -128,6 +128,7 @@ typedef enum {
         oGlobalKnownHostsFile2, oUserKnownHostsFile2, oPubkeyAuthentication,
         oKbdInteractiveAuthentication, oKbdInteractiveDevices, oHostKeyAlias,
         oDynamicForward, oPreferredAuthentications, oHostbasedAuthentication,
+        oUseBlacklistedKeys,
         oHostKeyAlgorithms, oBindAddress, oPKCS11Provider,
         oClearAllForwardings, oNoHostAuthenticationForLocalhost,
         oEnableSSHKeysign, oRekeyLimit, oVerifyHostKeyDNS, oConnectTimeout,
@@ -161,6 +162,7 @@ static struct {
         { "passwordauthentication", oPasswordAuthentication },
         { "kbdinteractiveauthentication", oKbdInteractiveAuthentication },
         { "kbdinteractivedevices", oKbdInteractiveDevices },
+        { "useblacklistedkeys", oUseBlacklistedKeys },
         { "rsaauthentication", oRSAAuthentication },
         { "pubkeyauthentication", oPubkeyAuthentication },
         { "dsaauthentication", oPubkeyAuthentication },             /* alias */
@@ -523,6 +525,10 @@ parse_flag:
                 intptr = &options->challenge_response_authentication;
                 goto parse_flag;
 
+        case oUseBlacklistedKeys:
+                intptr = &options->use_blacklisted_keys;
+                goto parse_flag;
+
         case oGssAuthentication:
                 intptr = &options->gss_authentication;
                 goto parse_flag;
@@ -1210,6 +1216,7 @@ initialize_options(Options * options)
         options->kbd_interactive_devices = NULL;
         options->rhosts_rsa_authentication = -1;
         options->hostbased_authentication = -1;
+        options->use_blacklisted_keys = -1;
         options->batch_mode = -1;
         options->check_host_ip = -1;
         options->strict_host_key_checking = -1;
@@ -1320,6 +1327,8 @@ fill_default_options(Options * options)
                 options->rhosts_rsa_authentication = 0;
         if (options->hostbased_authentication == -1)
                 options->hostbased_authentication = 0;
+        if (options->use_blacklisted_keys == -1)
+                options->use_blacklisted_keys = 0;
         if (options->batch_mode == -1)
                 options->batch_mode = 0;
         if (options->check_host_ip == -1)