Reset outside window - false alarm?

Thanks, it works after input the command.

Sophos didn't fix the bug on V17.5.3 MR-3...

I'm getting thousands upon thousands of these errors in my Sophos XG135 rev.3, it's showing nearly 50k just yesterday for an office of 7 people. I'm running 17.5.3 MR3. I can run the command on my console to disable the anomaly detection. But by doing so, am I disabling the ability to detect or use any IPS functionality?

Hey Brad Hall 

Copy and paste from here:

This specific IPS signature has been disabled by default, starting with SFOS v17.1.4 MR-4 due to customers experiencing excessive false-positives.

These IPS signatures are triggered by TCP anomalies (includes RST packets received outside of window). This was causing some customers to experience valid RST packets being false-positively dropped.

Customers still experiencing excessive false-positives should raise a support case for further investigation. However, this setting can also be disabled via the console command (set ips tcp_option detect_anomalies disable) to allow the TCP anomaly decision to be made by the host client OS instead if desired.

Regards,

Sorry for the late response.

Did the Console Command: set ips tcp_option detect_anomalies disable

Response: Already Configured

Since I was in the device. Updated firmware, Current Firmware: (SFOS 17.5.3 MR-3) 

I will monitor the errors and report back (sooner this time).

FloSupport I ran the command listed. Viewed my Firewall this morning and I now have 0 "attacks/errors" showing. It appears this took care of the issue over the weekend. I'll monitor and report back if I see any further items regarding this issue. 

I have two XG applainces, one 310 and 105w. On the XG310 17.5.0 GA and on XG105w 17.5.3 MR-3. On both devices I have "Data sent on stream after TCP Reset received"
Then on 105w I have done "set ips tcp_option detect_anomalies disable" and there is no more that kind of network intrusions in the last two hours. I will be watching and when it is ok I will try to implement this on bigger XG.

I am getting these as well, I did follow the KB, what confusing me is I am on XG105w 17.5.3 MR-3.  So I would think Sophos would have fixed this by now without me having to use the KB.  Since they still have the KB in place and are not sending the fix out with the latest release I am assuming that this is not completely fixed and the KB is a workaround until Sophos can figure out why there are so many false postives?  

What I am looking for here is why was it enabled in the first place and what threats am I exposing the network too if I disable it?

Hey Badrobot 

The fix to this issue was the setting being disabled by default starting with SFOS v17.1.4 MR-4, so I apologize as it seems this did not occur for you.

As I mentioned previously:

• This specific IPS signature has been disabled by default, starting with SFOS v17.1.4 MR-4 due to customers experiencing excessive false-positives.

  These IPS signatures are triggered by TCP anomalies (includes RST packets received outside of window). This was causing some customers to experience valid RST packets being false-positively dropped.

  Customers still experiencing excessive false-positives should raise a support case for further investigation. However, this setting can also be disabled via the console command (set ips tcp_option detect_anomalies disable) to allow the TCP anomaly decision to be made by the host client OS instead if desired.

Please continue to monitor and let me know if you run into any further issues.

Regards,

It is not true that TCP anomalies is disabled starting with SFOS v17.1.4 MR-4, at least on my Sophos Home machine.

I fresh installed it using 17.5.6 MR-5 ISO without loading any previous backup. It is automatically updated to MR6 when I active the license.

Login to console and found that "var DETECT_ANOMALIES" is set to "yes"

console> show ips_conf
config stream 1
config maxsesbytes 0
config stdsig 1
config qnum 10
config maxpkts 8
config disable_tcpopt_experimental_drops 0
config enable_appsignatures 1
var SEARCH_METHOD ac-q
var SIP_STATUS enabled
var IGNORE_CALL_CHANNEL enabled
var TCP_POLICY windows
var LOCAL_RULE local.rules
var DETECT_ANOMALIES yes
var TCP_BLOCK block
config failclose off
config cpulist 0:1

Run suggested command to disable anomalies detection:

console> set ips tcp_option detect_anomalies disable

Check the ips_conf again var DETECT_ANOMALIES" is set to "no"

console> show ips_conf
config stream 1
config maxsesbytes 0
config stdsig 1
config qnum 10
config maxpkts 8
config disable_tcpopt_experimental_drops 0
config enable_appsignatures 1
var SEARCH_METHOD ac-q
var SIP_STATUS enabled
var IGNORE_CALL_CHANNEL enabled
var TCP_POLICY windows
var LOCAL_RULE local.rules
var TCP_BLOCK nblock
config failclose off
config cpulist 0:1
var DETECT_ANOMALIES no

The bug still didn't fix in V17.5.6 MR-6.
User need to fix it with the console command...