Last Modified: Apr 17, 2026
Affected Product(s):
BIG-IP LTM
Known Affected Versions:
17.1.0, 17.1.0.1, 17.1.0.2, 17.1.0.3, 17.1.1, 17.1.1.1, 17.1.1.2, 17.1.1.3, 17.1.1.4, 17.1.2, 17.1.2.1, 17.1.2.2, 17.1.3, 17.1.3.1, 17.5.0, 17.5.1, 17.5.1.2, 17.5.1.3, 17.5.1.4, 17.5.1.5, 21.0.0, 21.0.0.1
Opened: Mar 04, 2026 Severity: 3-Major
Temporary listeners might not complete a connection under a syncookie mode.
BIG-IP may fail to establish a proxied TCP connection if it doesn’t complete the TCP three-way handshake with the pool member.
Occurs when, - Temporary listener is used for handling traffic (for example FTP). - Device under syncookie mode.
1. Disable syncookies. 2. Disable inheritance when possible. For example, FTP ephemeral listeners inherit syncookie behavior from the FTP virtual server; disabling inherit-parent-profile prevents the ephemeral listener from inheriting syncookies.
None