Bug ID 789857: "TCP half open' reports drops made by LTM syn-cookies mitigation.

Last Modified: Jul 12, 2023

Affected Product(s):
BIG-IP AFM(all modules)

Known Affected Versions:
14.1.0,,,,,, 14.1.2,,,,,,,,, 14.1.3,, 15.0.0, 15.0.1,,,,, 15.1.0,,,,,

Fixed In:
15.1.1, 14.1.4

Opened: Jun 04, 2019

Severity: 3-Major


'TCP half open' reports drops in logs/tmctl/AVR even though it is configured in detect-only mode.


It will appear that 'TCP half open' is doing mitigation, but it is actually LTM syn-cookies dropping the connections.


-- 'TCP half open' attack is being actively detected. -- LTM syn-cookie mitigation is enabled. -- This is triggered when LTM syn-cookies mitigation begins.


If LTM syn-cookies are not needed, disable the option: modify ltm global-settings connection default-vs-syn-challenge-threshold infinite global-syn-challenge-threshold infinite

Fix Information


Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips