Instituto Nacional de ciberseguridad. Sección Incibe
Instituto Nacional de Ciberseguridad. Sección INCIBE-CERT

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CVE-2026-21920

Severity CVSS v4.0:
HIGH
Type:
Unavailable / Other
Publication date:
15/01/2026
Last modified:
23/01/2026

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).<br /> <br /> <br /> <br /> <br /> 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.<br /> <br /> This issue affects Junos OS on SRX Series:<br /> <br /> <br /> <br /> * 23.4 versions before 23.4R2-S5,<br /> * 24.2 versions before 24.2R2-S1,<br /> * 24.4 versions before 24.4R2.<br /> <br /> <br /> <br /> <br /> <br /> <br /> This issue does not affect Junos OS versions before 23.4R1.

Impact

Vector 4.0
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/AU:Y/R:A/RE:M CVSS v4.0 Severity and Metrics:

Base Score: 8.70 HIGH
Vector: 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/AU:Y/R:A/RE:M

Attack Vector (AV): Network
Attack Complexity (AC): Low
Attack Requirements (AT): None
Privileges Required (PR): None
User Interaction (UI): None
Confidentiality (VC): None
Integrity (VI): None
Availability (VA): High
Confidentiality (SC): None
Integrity (SI): None
Availability (SA): Low
Automatable (AU): Yes
Recovery (R): Automatic
Vulnerability Response Effort (RE): Moderate

Base Score 4.0
8.70
Severity 4.0
HIGH
Vector 3.x
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS v3.1 Severity and Metrics:

Base Score: 7.50 HIGH
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): None
Integrity (I): None
Availability (A): High

Base Score 3.x
7.50
Severity 3.x
HIGH

Vulnerable products and versions

CPE From Up to
cpe:2.3:o:juniper:junos:23.4:-:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r1-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r1-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r2-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r2-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r2-s3:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:23.4:r2-s4:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:24.2:-:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:24.2:r1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:24.2:r1-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:24.2:r1-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:24.2:r2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:24.4:-:*:*:*:*:*:*

To consult the complete list of CPE names with products and versions, see this page


References to Advisories, Solutions, and Tools