CVE-2024-39561Network attack vector

Firewall bypass via mishandled SYN flag combinations

Published Jul 10, 2024 · Updated Aug 2, 2024

Improper exceptional-condition handling in Junos OS on SRX4600 and SRX5000 Series allows remote attackers to bypass TCP filtering. When no-syn-check and Express Path are enabled, flowd forwards SYN/FIN and SYN/RST packets downstream instead of dropping them. The non-default configuration is required, and the consequence is limited to unintended passage of crafted TCP traffic through the firewall.

CVSS severity6.9
Medium
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper exceptional-condition handling in Junos OS on SRX4600 and SRX5000 Series allows remote attackers to bypass TCP filtering. When no-syn-check and Express Path are enabled, flowd forwards SYN/FIN and SYN/RST packets downstream instead of dropping them. The non-default configuration is required, and the consequence is limited to unintended passage of crafted TCP traffic through the firewall.

The record

CVE
CVE-2024-39561
Published
Jul 10, 2024
Updated
Aug 2, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-754, T1562.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 10, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <21.2r3-s8
  2. Affected versionversion=0 <21.2R3-S8
  3. Affected versionversion=21.4 <21.4r3-s7
  4. Affected versionversion=21.4 <21.4R3-S7
  5. Affected versionversion=22.1 <22.1R3-S6
  6. Affected versionversion=22.2 <22.2r3-s4
  7. Affected versionversion=22.2 <22.2R3-S4
  8. Affected versionversion=22.3 <22.3r3-s3
  9. Affected versionversion=22.3 <22.3R3-S3
  10. Affected versionversion=22.4 <22.4r3-s2
  11. Affected versionversion=22.4 <22.4R3-S2
  12. Affected versionversion=23.2 <23.2r2
  13. Affected versionversion=23.2 <23.2R2
  14. Affected versionversion=23.4 <23.4R1-S1, 23.4R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=0 <21.2r3-s8; version=0 <21.2R3-S8; version=21.4 <21.4r3-s7; version=21.4 <21.4R3-S7; version=22.1 <22.1R3-S6; version=22.2 <22.2r3-s4; version=22.2 <22.2R3-S4; version=22.3 <22.3r3-s3; version=22.3 <22.3R3-S3; version=22.4 <22.4r3-s2; version=22.4 <22.4R3-S2; version=23.2 <23.2r2; version=23.2 <23.2R2; version=23.4 <23.4R1-S1, 23.4R2

Published CVSS scores

5.8Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
6.9Juniper NetworksCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
T1562.004Disable or Modify System Firewall

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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