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Fencer Vulns
medium 5.8

CVE-2024-39561 json

Junos OS: SRX4600, SRX5000 Series: TCP packets with SYN/FIN or SYN/RST are transferred after enabling no-syn-check with Express Path

published 2024-07-10 2 y ago modified 2026-06-17 4 mo ago also EUVD-2024-38087

cvss
5.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits
0
none known

Summary

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.

Patch / fix

  • Juniper Networks Junos OS 21.2R3-S8, 21.4R3-S7, 22.1R3-S6, 22.2R3-S4, 22.3R3-S3, 22.4R3-S2, 23.2R2, 23.4R1-S1, 23.4R2
  • juniper junos 21.2r3-s8, 21.4r3-s7, 22.2r3-s4, 22.3r3-s3, 22.4r3-s2, 23.2r2

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.31% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
CNA 4.0 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
CNA 4.0 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

  • Juniper Networks Junos OS
  • juniper junos

Classification

Weakness
  • CWE-754 Improper Check for Unusual or Exceptional Conditions

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.