Security: Cross Protocol Scripting protection.

This is an attempt at mitigating problems due to cross protocol
scripting, an attack targeting services using line oriented protocols
like Redis that can accept HTTP requests as valid protocol, by
discarding the invalid parts and accepting the payloads sent, for
example, via a POST request.

For this to be effective, when we detect POST and Host: and terminate
the connection asynchronously, the networking code was modified in order
to never process further input. It was later verified that in a
pipelined request containing a POST command, the successive commands are
not executed.

src/networking.c

@@ -1242,8 +1242,10 @@ void processInputBuffer(client *c) {
 
         /* CLIENT_CLOSE_AFTER_REPLY closes the connection once the reply is
          * written to the client. Make sure to not let the reply grow after
-         * this flag has been set (i.e. don't process more commands). */
-        if (c->flags & CLIENT_CLOSE_AFTER_REPLY) break;
+         * this flag has been set (i.e. don't process more commands).
+         *
+         * The same applies for clients we want to terminate ASAP. */
+        if (c->flags & (CLIENT_CLOSE_AFTER_REPLY|CLIENT_CLOSE_ASAP)) break;
 
         /* Determine request type when unknown. */
         if (!c->reqtype) {
@@ -1610,6 +1612,26 @@ void clientCommand(client *c) {
     }
 }
 
+/* This callback is bound to POST and "Host:" command names. Those are not
+ * really commands, but are used in security attacks in order to talk to
+ * Redis instances via HTTP, with a technique called "cross protocol scripting"
+ * which exploits the fact that services like Redis will discard invalid
+ * HTTP headers and will process what follows.
+ *
+ * As a protection against this attack, Redis will terminate the connection
+ * when a POST or "Host:" header is seen, and will log the event from
+ * time to time (to avoid creating a DOS as a result of too many logs). */
+void securityWarningCommand(client *c) {
+    static time_t logged_time;
+    time_t now = time(NULL);
+
+    if (labs(now-logged_time) > 60) {
+        serverLog(LL_WARNING,"Possible SECURITY ATTACK detected. It looks like somebody is sending POST or Host: commands to Redis. This is likely due to an attacker attempting to use Cross Protocol Scripting to compromise your Redis instance. Connection aborted.");
+        logged_time = now;
+    }
+    freeClientAsync(c);
+}
+
 /* Rewrite the command vector of the client. All the new objects ref count
  * is incremented. The old command vector is freed, and the old objects
  * ref count is decremented. */

src/server.c

@@ -296,6 +296,8 @@ struct redisCommand redisCommandTable[] = {
     {"pfcount",pfcountCommand,-2,"r",0,NULL,1,-1,1,0,0},
     {"pfmerge",pfmergeCommand,-2,"wm",0,NULL,1,-1,1,0,0},
     {"pfdebug",pfdebugCommand,-3,"w",0,NULL,0,0,0,0,0},
+    {"post",securityWarningCommand,-1,"lt",0,NULL,0,0,0,0,0},
+    {"host:",securityWarningCommand,-1,"lt",0,NULL,0,0,0,0,0},
     {"latency",latencyCommand,-2,"aslt",0,NULL,0,0,0,0,0}
 };
 

src/server.h

@@ -1812,6 +1812,7 @@ void pfmergeCommand(client *c);
 void pfdebugCommand(client *c);
 void latencyCommand(client *c);
 void moduleCommand(client *c);
+void securityWarningCommand(client *c);
 
 #if defined(__GNUC__)
 void *calloc(size_t count, size_t size) __attribute__ ((deprecated));