CVE-2026-21920

moderate-risk

Published 2026-01-15

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.

Do I need to act?

0.02% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 7.5/10 High

NETWORK / LOW complexity

Affected Products (18)

Junos

Affected Vendors

Juniper

References (2)

Vendor Advisory https://kb.juniper.net/JSA106020

Vendor Advisory https://supportportal.juniper.net/JSA106020

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moderate-risk

Severity 26/34 · High

Exploitability 0/34 · Minimal

Exposure 19/34 · Moderate