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High severity · published Jan 15, 2026
CVE-2026-21918
Junos OS: SRX and MX Series: When TCP packets occur in a specific sequence flowd crashes
7.5
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 35% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
JO
Junos OS · Juniper
before 22.4R3-S7; 23.2 before 23.2R2-S3; 23.4 before 23.4R2-S4; 24.2 before 24.2R2 · source: vendor, NVD
Affected product
JO
Junos OS
Juniper
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-21918
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-21918
Vendor Advisory
https://kb.juniper.net/JSA106018
Vendor Advisory
https://supportportal.juniper.net/JSA106018
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