Bug#706739: Asterisk do not log source IP for Fake auth rejection

[Dominik Strnad]

Package: Asterisk
Version: 1.6.2.9-2+squeeze10

As mentioned on Diginum forum:
http://forums.digium.com/viewtopic.php?t=78988
http://forums.digium.com/viewtopic.php?t=77070
http://forums.asterisk.org/viewtopic.php?t=74947

Problem: Asterisk 1.6 do not log source IP address used for brute force attacks in some cases. Thus usage of Fail2ban or other tools is limited.

Details: When using alwaysauthreject=yes in sip.conf, then source IP of attacker is not logged when rejecting INVITES from not registered devices trying to authenticate at call beginning (only asterisk server IP itself is logged).

Solution: As Diginum will not solve this issue even this problem concerns a lot of users, I created small patch solving this it, allowing fail2ban correctly handling such brute force attacks.

Before patch:

[2013-04-28 19:33:01] NOTICE[32446] chan_sip.c: Sending fake auth rejection for device 1011<sip:1011 at 10.98.231.154:5060>;tag=3b82edc2

After patch:

[2013-05-04 05:10:07] NOTICE[10851] chan_sip.c: Sending fake auth rejection for device '303<sip:303 at 10.98.231.154:5060>;tag=d9210d45' to '94.23.59.135'

patch:

--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -20238,7 +20238,7 @@
                 }
                 if (res < 0) { /* Something failed in authentication */
                         if (res == AUTH_FAKE_AUTH) {
-                               ast_log(LOG_NOTICE, "Sending fake auth rejection for device %s\n", get_header(req, "From"));
+                               ast_log(LOG_NOTICE, "Sending fake auth rejection for device '%s' to '%s'\n", get_header(req, "From"), ast_inet_ntoa(sin->sin_addr));
                                 transmit_fake_auth_response(p, SIP_INVITE, req, XMIT_RELIABLE);
                         } else {
                                 ast_log(LOG_NOTICE, "Failed to authenticate device %s\n", get_header(req, "From"));
@@ -21532,7 +21532,7 @@
                 return 0;
         if (res < 0) {
                 if (res == AUTH_FAKE_AUTH) {
-                       ast_log(LOG_NOTICE, "Sending fake auth rejection for device %s\n", get_header(req, "From"));
+                       ast_log(LOG_NOTICE, "Sending fake auth rejection for device '%s' to '%s'\n", get_header(req, "From"), ast_inet_ntoa(sin->sin_addr));
                         transmit_fake_auth_response(p, SIP_SUBSCRIBE, req, XMIT_UNRELIABLE);
                 } else {
                         ast_log(LOG_NOTICE, "Failed to authenticate device %s for SUBSCRIBE\n", get_header(req, "From"));


I would welcome possibility to this patch be inherited in next Debian Asterisk package. :-)

Best Regard
Dominik Strnad