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CVE-2026-21920

HIGHCVSS 8.7/10EPSS 0.44%

Last modified

CVE-2026-21920 is a high-severity vulnerability rated 8.7/10 on the CVSS scale. 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.. EPSS estimates a 0.44% chance of exploitation in the next 30 days.

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.

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
0.44%

35.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
JuniperJunos23.4
JuniperJunos24.2
JuniperJunos24.4

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-21920?
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.
How severe is CVE-2026-21920?
CVE-2026-21920 has a CVSS score of 8.7/10 (HIGH severity). The EPSS model estimates a 0.44% probability of exploitation in the next 30 days.
How do I fix CVE-2026-21920?
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-2026-21920?

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

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Source: NVD / NIST