BugZero | F5 BugID 853081 - FastL4: Tear-down connection with RST when SEQ equ...

F5 - Defect ID: 853081

FastL4: Tear-down connection with RST when SEQ equals last received ACK.

F5 - Defect ID: 853081

FastL4: Tear-down connection with RST when SEQ equals last received ACK.

Last updated on July 18th, 2026

BugZero Risk Score
6.2 Medium

Overall: 6.2

Severity: 6.4

Community: 4.2

Lifecycle: 10.0

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Bug Details

Priority: 4-Minor
Status: Resolved
Impact Category: Local Traffic Manager

Description

Symptoms

In a corner case when BIG-IP FastL4 virtual server receives a RST with a sequence number going back in a sequence space, but the sequence number is matching the last received ACK on the opposite side of the connection, connection may not be closed. RST is still forwarded if TM.ICSAStrictTcpForwarding is disabled.

Impact

Connection remains in the connection table until idle timeout is reached.

Conditions

-- FastL4 profile is in use. -- FastL4 virtual server receives a RST with a sequence number going back in a sequence space, but the sequence number is matching the last received ACK on the opposite side of the connection

Workaround

None.

Fix Information

None

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, 13.0.0, 13.0.0 hf1, 13.0.0 hf2, 13.0.0 hf3, 13.0.1, 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, 14.0.0, 14.0.0.1, 14.0.0.2, 14.0.0.3, 14.0.0.4, 14.0.0.5, 14.0.1, 14.0.1.1, 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, 15.0.0, 15.0.1, 15.0.1.1, 15.0.1.2, 15.0.1.3, 15.0.1.4, 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, 15.1.7, 15.1.8, 15.1.8.1, 15.1.8.2, 15.1.9, 15.1.9.1, 15.1.10, 15.1.10.2, 15.1.10.3, 15.1.10.4, 15.1.10.5, 15.1.10.6, 15.1.10.7, 15.1.10.8, 16.0.0, 16.0.0.1, 16.0.1, 16.0.1.1, 16.0.1.2

Fixed versions: No known fixed versions

Relevant Products

Click on a version to see all relevant bugs

Fixed versions: No known fixed versions

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F5 - Defect ID: 853081

FastL4: Tear-down connection with RST when SEQ equals last received ACK.

F5 - Defect ID: 853081

FastL4: Tear-down connection with RST when SEQ equals last received ACK.

Last updated on July 18th, 2026

BugZero Risk Score6.2 Medium

Bug Details

Symptoms

Impact

Conditions

Workaround

Fix Information

Links

Top F5 Defects

Ready to prevent the next vendor outage?

F5 - Defect ID: 853081

FastL4: Tear-down connection with RST when SEQ equals last received ACK.

F5 - Defect ID: 853081

FastL4: Tear-down connection with RST when SEQ equals last received ACK.

Last updated on July 18th, 2026

BugZero Risk Score6.2 Medium

Bug Details

Symptoms

Impact

Conditions

Workaround

Fix Information

Links

Top F5 Defects

Ready to prevent the next vendor outage?

BugZero Risk Score
6.2 Medium

BugZero Risk Score
6.2 Medium