CVE-2026-21918Network attack vector

Unauthenticated FPC restart via TCP-session double free

Published Jan 15, 2026 · Updated Jan 15, 2026

Double free in Juniper Networks Junos OS on SRX and MX Series allows remote attackers to restart an FPC during TCP session setup. During TCP session establishment, flowd frees the same allocation twice when it encounters a specific packet sequence, causing the daemon to crash. No authentication or user interaction is required, and the resulting FPC restart interrupts traffic handled by that card.

CVSS severity8.7
High
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in Juniper Networks Junos OS on SRX and MX Series allows remote attackers to restart an FPC during TCP session setup. During TCP session establishment, flowd frees the same allocation twice when it encounters a specific packet sequence, causing the daemon to crash. No authentication or user interaction is required, and the resulting FPC restart interrupts traffic handled by that card.

The record

CVE
CVE-2026-21918
Published
Jan 15, 2026
Updated
Jan 15, 2026
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-415, T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 15, 2026Record 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 <22.4R3-S7
  2. Affected versionversion=23.2 <23.2R2-S3
  3. Affected versionversion=23.4 <23.4R2-S4
  4. Affected versionversion=24.2 <24.2R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=0 <22.4R3-S7; version=23.2 <23.2R2-S3; version=23.4 <23.4R2-S4; version=24.2 <24.2R2

Published CVSS scores

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

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-415Double Free
T1498Network Denial of Service

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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