CVE-2024-39540Network attack vector

Service interruption via valid TCP traffic

Published Jul 11, 2024 · Updated Aug 2, 2024

Denial of service in the PFE of Juniper Networks Junos OS 21.2R3-S5 allows remote attackers to crash it with valid TCP traffic. The Packet Forwarding Engine mishandles an undisclosed exceptional condition while processing specific valid TCP traffic, causing the PFE to restart. No authentication or user interaction is required; the restart produces a momentary complete service outage on SRX Series devices and MX Series devices with SPC3.

CVSS severity8.7
High
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the PFE of Juniper Networks Junos OS 21.2R3-S5 allows remote attackers to crash it with valid TCP traffic. The Packet Forwarding Engine mishandles an undisclosed exceptional condition while processing specific valid TCP traffic, causing the PFE to restart. No authentication or user interaction is required; the restart produces a momentary complete service outage on SRX Series devices and MX Series devices with SPC3.

The record

CVE
CVE-2024-39540
Published
Jul 11, 2024
Updated
Aug 2, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-754, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 11, 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=21.2 <21.2r3-s6
  2. Affected versionversion=21.2R3-S5 <21.2R3-S6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=21.2 <21.2r3-s6; version=21.2R3-S5 <21.2R3-S6

Published CVSS scores

7.5Juniper Networks, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7Juniper Networks, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 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
T1499.004Application or System Exploitation

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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