CVE-2026-21918

Name: CVE-2026-21918
Creator: NVD / NIST
Published: 2026-01-15T21:16:08.05+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.7/10EPSS 0.38%

Last modified Jun 17, 2026

CVE-2026-21918 is a high-severity vulnerability rated 8.7/10 on the CVSS scale. A Double Free vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX and MX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). On all SRX and MX Series platforms, when during TCP session establishment a specific sequence of packets is encountered a double free happens. EPSS estimates a 0.38% chance of exploitation in the next 30 days.

Description

A Double Free vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX and MX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). On all SRX and MX Series platforms, when during TCP session establishment a specific sequence of packets is encountered a double free happens. This causes flowd to crash and the respective FPC to restart. This issue affects Junos OS on SRX and MX Series: * all versions before 22.4R3-S7, * 23.2 versions before 23.2R2-S3, * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R2.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS 4.0

8.7/10

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/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:Y/R:A/V:X/RE:M/U:X

EPSS Probability

0.38%

29.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-415

Affected Software

Vendor	Product	Versions
Juniper	Junos	< 22.4
Juniper	Junos	22.4
Juniper	Junos	23.2
Juniper	Junos	23.4
Juniper	Junos	24.2

References

https://kb.juniper.net/JSA106018Vendor Advisory
https://supportportal.juniper.net/JSA106018Vendor Advisory

Timeline

Published: Jan 15, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-21918?

How severe is CVE-2026-21918?

CVE-2026-21918 has a CVSS score of 8.7/10 (HIGH severity). The EPSS model estimates a 0.38% probability of exploitation in the next 30 days.

How do I fix CVE-2026-21918?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-21918?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST