BugZero | F5 BugID 1075421 - Connections can fail when hardware syncookie mode ...

F5 - Defect ID: 1075421

Connections can fail when hardware syncookie mode is activated.

F5 - Defect ID: 1075421

Connections can fail when hardware syncookie mode is activated.

Last updated on July 18th, 2026

BugZero Risk Score
6.9 Medium

Overall: 6.9

Severity: 7.3

Community: 4.2

Lifecycle: 8.7

What is the BugZero Risk Score?

F5 Integration

Learn more about where this data comes from

F5 Integration

Learn more

BugZero Plan

Streamline upgrades with automated vendor bug scrubs

BugZero Plan

Learn more

BugZero Prevent

Wish you caught this bug sooner? Get proactive today.

BugZero Prevent

Learn more

Bug Details

Priority: 3-Major
Status: Resolved
Impact Category: Advanced Firewall Manager
Views: 2

Description

Symptoms

If a virtual server is in hardware syncookie mode and it is forwarded to TMM0, then the connection can fail. This can happen if CMP demote mode is used, which is possible with certain iRules. You can observe this using a packet capture where the frame is received on non-TMM0 and a RST frame with 'No flow found for ACK' is sent from TMM0.

Impact

Connection fails when all TMMs except TMM0 are targeted.

Conditions

CMP demotion is used. The common cause of this is a non-CMP compatible iRule as described in K13033. There can be other causes.

Workaround

Prevent CMP demotion. This depends on the cause, but one common cause is due to a non-CMP compatible iRule as described in K13033.

Fix Information

N/A

Change history

Links

Original Vendor Announcement

Relevant Products

Click on a version to see all relevant bugs

Affected versions:12.1.0, 12.1.0 hf1, 12.1.0 hf2, 12.1.1, 12.1.1 hf1, 12.1.1 hf2, 12.1.2, 12.1.2 hf1, 12.1.2 hf2, 12.1.3, 12.1.3.1, 12.1.3.2, 12.1.3.3, 12.1.3.4, 12.1.3.5, 12.1.3.6, 12.1.3.7, 12.1.4, 12.1.4.1, 12.1.5, 12.1.5.1, 12.1.5.2, 12.1.5.3, 12.1.6, 13.1.0, 13.1.0.1, 13.1.0.2, 13.1.0.3, 13.1.0.4, 13.1.0.5, 13.1.0.6, 13.1.0.7, 13.1.0.8, 13.1.1, 13.1.1.2, 13.1.1.3, 13.1.1.4, 13.1.1.5, 13.1.3, 13.1.3.1, 13.1.3.2, 13.1.3.3, 13.1.3.4, 13.1.3.5, 13.1.3.6, 13.1.4, 13.1.4.1, 13.1.5, 13.1.5.1, 14.1.0, 14.1.0.1, 14.1.0.2, 14.1.0.3, 14.1.0.5, 14.1.0.6, 14.1.2, 14.1.2.1, 14.1.2.2, 14.1.2.3, 14.1.2.4, 14.1.2.5, 14.1.2.6, 14.1.2.7, 14.1.2.8, 14.1.3, 14.1.3.1, 14.1.4, 14.1.4.1, 14.1.4.2, 14.1.4.3, 14.1.4.4, 14.1.4.5, 14.1.4.6, 14.1.5, 14.1.5.1, 14.1.5.2, 14.1.5.3, 14.1.5.4, 14.1.5.6, 15.1.0, 15.1.0.1, 15.1.0.2, 15.1.0.3, 15.1.0.4, 15.1.0.5, 15.1.1, 15.1.2, 15.1.2.1, 15.1.3, 15.1.3.1, 15.1.4, 15.1.4.1, 15.1.5, 15.1.5.1, 15.1.6, 15.1.6.1, 16.0.0, 16.0.0.1, 16.0.1, 16.0.1.1, 16.0.1.2, 16.1.0, 16.1.1, 16.1.2, 16.1.2.1, 16.1.2.2, 16.1.3, 16.1.3.1, 16.1.3.2, 16.1.3.3, 16.1.3.4, 16.1.3.5

Fixed versions: 17.0.0, 16.1.4, 15.1.7

Relevant Products

Click on a version to see all relevant bugs

Fixed versions: 17.0.0, 16.1.4, 15.1.7

Top F5 Defects

9.6Defect ID: 546260
TMM can crash if using the v6rd profile
9.6Defect ID: 934133
Unable to Create/delete ltm virtual server via CLI transaction when destination is not specified on the ltm virtual object
9.6Defect ID: 1154417
Profile based attack is not mitigated at hardware on L2 wire setup
9.6Defect ID: 913713
Rebooting a blade causes MCPd to core as it rejoins the cluster
9.6Defect ID: 2141125
Multicast traffic is dropped with incorrect VLAN tagging

F5 Integration

Learn more about where this data comes from

F5 Integration

Learn more

BugZero Plan

Streamline upgrades with automated vendor bug scrubs

BugZero Plan

Learn more

BugZero Prevent

Wish you caught this bug sooner? Get proactive today.

BugZero Prevent

Learn more

Ready to prevent the next vendor outage?

Get a demo

F5 - Defect ID: 1075421

Connections can fail when hardware syncookie mode is activated.

F5 - Defect ID: 1075421

Connections can fail when hardware syncookie mode is activated.

Last updated on July 18th, 2026

BugZero Risk Score6.9 Medium

Bug Details

Symptoms

Impact

Conditions

Workaround

Fix Information

Links

Top F5 Defects

Ready to prevent the next vendor outage?

F5 - Defect ID: 1075421

Connections can fail when hardware syncookie mode is activated.

F5 - Defect ID: 1075421

Connections can fail when hardware syncookie mode is activated.

Last updated on July 18th, 2026

BugZero Risk Score6.9 Medium

Bug Details

Symptoms

Impact

Conditions

Workaround

Fix Information

Links

Top F5 Defects

Ready to prevent the next vendor outage?

BugZero Risk Score
6.9 Medium

BugZero Risk Score
6.9 Medium