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I'm getting thousands of these a day, most times (99.99%) with internal sources, sometimes with an external source.Firmware is 17.1.3 MR3
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.
In reply to FloSupport:
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?
In reply to 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.
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_confconfig stream 1config maxsesbytes 0config stdsig 1config qnum 10config maxpkts 8config disable_tcpopt_experimental_drops 0config enable_appsignatures 1var SEARCH_METHOD ac-qvar SIP_STATUS enabledvar IGNORE_CALL_CHANNEL enabledvar TCP_POLICY windowsvar LOCAL_RULE local.rulesvar DETECT_ANOMALIES yesvar TCP_BLOCK blockconfig failclose offconfig 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_confconfig stream 1config maxsesbytes 0config stdsig 1config qnum 10config maxpkts 8config disable_tcpopt_experimental_drops 0config enable_appsignatures 1var SEARCH_METHOD ac-qvar SIP_STATUS enabledvar IGNORE_CALL_CHANNEL enabledvar TCP_POLICY windowsvar LOCAL_RULE local.rulesvar TCP_BLOCK nblockconfig failclose offconfig cpulist 0:1var DETECT_ANOMALIES no
The bug still didn't fix in V17.5.6 MR-6.User need to fix it with the console command...
We have an update. TCP anomalies detection will be disabled by default starting from v17.5 MR-8. Please check the updated article: Sophos XG Firewall: IPS causing drops to legitimate traffic and filling the IPS log
In reply to Jaydeep:
does disabling TCP anomalies detection also lower the detection rate of the IPS system?
In reply to Dwayne Parker:
Yesterday I installed XG310 (SFOS 17.5.3 MR-3) at client site.
It is in bridge mode after MKtik router doing NAT+Routing+VPN+basic FW.
Still there are a TON of false IPS positives. TCP related, IMAP related, Print spooler related(just some broadcasts), DNS related(replies from 220.127.116.11).
So this is redicilous.
Disabling is just temp solution? Even in upgrade does it stop/lower efficiency of IPS?
Have a nice day! Greetings!
does anybody know if this is lowering the detectionrate of the IPS?
I just want to ask again, if somebody knows if disabling "Anomaly Detection" lowers the detection/protection rate of the IPS system.
Is this issue solved in v18 EAP, so that Anomaly Detection is working again?
In reply to Kaloian Kirchev:
Hi Kaloian Kirchev
This issue is resolved in SFOS v17.5.8 MR-8. By default the setting will be enabled, as it was causing too many false positive detections.
Thanks for the reply. BUT could you please answer the questions above.
Is disabling IPS anomalies LOWERs the protection and effectiveness?
Have a nice day!
Yes, disabling any IPS setting/signature affects protection somewhat.
This particular IPS setting detects and drops "anomalous" TCP traffic (missing TCP timestamps, etc.) This setting was causing excessive false-positives & issues for some customers, therefore the option to disable it was provided.
Copy and paste of the information I provided previously: