High severity · published Jan 15, 2026
CVE-2026-21920
Junos OS: SRX Series: If a specific request is processed by the DNS subsystem flowd will crash
7.5
CVSS
0.5%
EPSS
No
On KEV
Description
An Unchecked Return Value vulnerability in the DNS module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).
If an SRX Series device configured for DNS processing, receives a specifically formatted DNS request flowd will crash and restart, which causes a service interruption until the process has recovered.
This issue affects Junos OS on SRX Series:
* 23.4 versions before 23.4R2-S5,
* 24.2 versions before 24.2R2-S1,
* 24.4 versions before 24.4R2.
This issue does not affect Junos OS versions before 23.4R1.
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)0.5% · higher than 41% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
JO
Junos OS · Juniper
23.4 before 23.4R2-S5; 24.2 before 24.2R2-S1; 24.4 before 24.4R2 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-21920
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-21920
Vendor Advisory
https://kb.juniper.net/JSA106020
Vendor Advisory
https://supportportal.juniper.net/JSA106020
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