BugZero | F5 BugID 502683 - Traffic intermittently dropped in syncookie mode, ...

F5 - Defect ID: 502683

Traffic intermittently dropped in syncookie mode, especially when hardware syncookie is on

F5 - Defect ID: 502683

Traffic intermittently dropped in syncookie mode, especially when hardware syncookie is on

Last updated on July 18th, 2026

BugZero Risk Score
6.7 Medium

Overall: 6.7

Severity: 7.3

Community: 4.2

Lifecycle: 7.0

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: Verified
Impact Category: Local Traffic Manager

Description

Symptoms

In certain corner cases, BIG-IP software rejects valid SYN-Cookie responses due to incorrect hardware algorithm masking on the software side.

Impact

Intermittent connection failures.

Conditions

This issue appears only on hardware-SYN-Cookie-capable platforms when running the hardware SYN-Cookie algorithm.

Workaround

Run software SYN-Cookie algorithm. Use the DB variable. This makes sure software is running correct generation and validation algorithm.

Fix Information

Traffic is now handled correctly in certain corner cases involving hardware syncookies.

Change history

Links

Original Vendor Announcement

Relevant Products

Click on a version to see all relevant bugs

Affected versions:11.5.1, 11.5.1 hf1, 11.5.1 hf2, 11.5.1 hf3, 11.5.1 hf4, 11.5.1 hf5, 11.5.1 hf6, 11.5.1 hf7, 11.5.1 hf8, 11.5.1 hf9, 11.5.1 hf10, 11.5.1 hf11, 11.5.2, 11.5.2 hf1, 11.6.0, 11.6.0 hf1, 11.6.0 hf2, 11.6.0 hf3, 11.6.0 hf4, 11.6.0 hf5, 11.6.0 hf6, 11.6.0 hf7, 11.6.0 hf8, 11.6.1, 11.6.1 hf1, 11.6.1 hf2, 11.6.2, 11.6.2 hf1, 11.6.3, 11.6.3.1, 11.6.3.2, 11.6.3.3, 11.6.3.4, 11.6.4, 11.6.5, 11.6.5.1, 11.6.5.2, 11.6.5.3

Fixed versions: 12.0.0, 11.5.3

Relevant Products

Click on a version to see all relevant bugs

Fixed versions: 12.0.0, 11.5.3

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: 502683

Traffic intermittently dropped in syncookie mode, especially when hardware syncookie is on

F5 - Defect ID: 502683

Traffic intermittently dropped in syncookie mode, especially when hardware syncookie is on

Last updated on July 18th, 2026

BugZero Risk Score6.7 Medium

Bug Details

Symptoms

Impact

Conditions

Workaround

Fix Information

Links

Top F5 Defects

Ready to prevent the next vendor outage?

F5 - Defect ID: 502683

Traffic intermittently dropped in syncookie mode, especially when hardware syncookie is on

F5 - Defect ID: 502683

Traffic intermittently dropped in syncookie mode, especially when hardware syncookie is on

Last updated on July 18th, 2026

BugZero Risk Score6.7 Medium

Bug Details

Symptoms

Impact

Conditions

Workaround

Fix Information

Links

Top F5 Defects

Ready to prevent the next vendor outage?

BugZero Risk Score
6.7 Medium

BugZero Risk Score
6.7 Medium