CVE-2026-21920: Junos OS: SRX Series: If a specific request is processed by the DNS subsystem flowd will crash

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-01-15 · updated 2026-06-17
Weakness: CWE-252

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.

Affected products

Juniper Junos OS: 23.4, 23.4-r1, 23.4-r1-s1, 23.4-r1-s2, 23.4-r2, 23.4-r2-s1 (+12)

References

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