The earliest recollection of this bug is traced back to PAN-OS 8.1.17 - January 09, 2024. This bug is fixed in PAN-OS versions 9.1.5, 8.1.17. A fix was made to address a vulnerability in the PAN-OS signature-based threat detection engine that allowed an attacker to evade threat prevention signatures using specifically crafted TCP packets ( CVE-2020-1999 ). For more information: https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-release-notes/pan-os-8-1-addressed-issues/pan-os-8-1-17-addressed-issues https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-addressed-issues/pan-os-9-1-5-addressed-issues