An Improper Check for Unusual or Exceptional Conditions vulnerability in the flow daemon (flowd) of Juniper Networks Junos OS on SRX4600 and SRX5000 Series allows an attacker to send TCP packets with SYN/FIN or SYN/RST flags, bypassing the expected blocking of these packets. A TCP packet with SYN/FIN or SYN/RST should be dropped in flowd. However, when no-syn-check and Express Path are enabled, these TCP packets are unexpectedly transferred to the downstream network.

This issue affects Junos OS on SRX4600 and SRX5000 Series: All versions before 21.2R3-S8, from 21.4 before 21.4R3-S7, from 22.1 before 22.1R3-S6, from 22.2 before 22.2R3-S4, from 22.3 before 22.3R3-S3, from 22.4 before 22.4R3-S2, from 23.2 before 23.2R2, from 23.4 before 23.4R1-S1, 23.4R2.