Last Modified: Apr 22, 2026
Affected Product(s):
BIG-IP LTM
Known Affected Versions:
16.1.6.1, 17.1.3.1, 17.5.1.5, 21.0.0, 21.0.0.1
Opened: Apr 16, 2026 Severity: 3-Major
BIG-IP advertises non-zero window in SYN/SYN-ACK (as expected), but zero window in the final 3WHS ACK and in all subsequent packets, stalling the tcp connection forever.
All tcp connections get stalled, both on the client-side and on the server-side.
Virtual server configured with a tcp profile having a Receive Window value ('receive-window-size' in tmsh) between 536862721 and 1073725440
Two possible workarounds. - Configure a Receive Window value ('receive-window-size' in tmsh) to any value lower than 536862721. - On the tcp profile, set the Initial Receive Window Size ('init-rwnd' in tmsh) to 64
None