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, 26 insertions, 1 deletions

diff --git a/auth.c b/auth.c
index 9a36f1dac..6662e9a75 100644
--- a/auth.c
+++ b/auth.c
@@ -59,6 +59,7 @@
 #include "servconf.h"
 #include "key.h"
 #include "hostfile.h"
+#include "authfile.h"
 #include "auth.h"
 #include "auth-options.h"
 #include "canohost.h"
@@ -657,10 +658,34 @@ getpwnamallow(const char *user)
 
 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */
 int
-auth_key_is_revoked(Key *key)
+auth_key_is_revoked(Key *key, int hostkey)
 {
         char *key_fp;
 
+        if (blacklisted_key(key, &key_fp) == 1) {
+                if (options.permit_blacklisted_keys) {
+                        if (hostkey)
+                                error("Host key %s blacklisted (see "
+                                    "ssh-vulnkey(1)); continuing anyway",
+                                    key_fp);
+                        else
+                                logit("Public key %s from %s blacklisted (see "
+                                    "ssh-vulnkey(1)); continuing anyway",
+                                    key_fp, get_remote_ipaddr());
+                        free(key_fp);
+                } else {
+                        if (hostkey)
+                                error("Host key %s blacklisted (see "
+                                    "ssh-vulnkey(1))", key_fp);
+                        else
+                                logit("Public key %s from %s blacklisted (see "
+                                    "ssh-vulnkey(1))",
+                                    key_fp, get_remote_ipaddr());
+                        free(key_fp);
+                        return 1;
+                }
+        }
+
         if (options.revoked_keys_file == NULL)
                 return 0;
         switch (ssh_krl_file_contains_key(options.revoked_keys_file, key)) {