Cyber Resilience

CVE-2026-21919

Juniper Junos 23.4 … 24.4

Published
09 April 2026
Modified
17 April 2026
Patch / advisory
CVSS Score v4 7.1
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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:U/V:X/RE:M/U:X
EPSS Score 0.0023 14th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-21919 is a high-severity Incorrect Synchronization (CWE-821) vulnerability in Juniper Junos. Its CVSS base score is 7.1 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 14th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SC-4 (Information in Shared System Resources) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

An Incorrect Synchronization vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a network-based attacker with low privileges to cause a complete Denial-of-Service (DoS) of the management plane. When NETCONF sessions are quickly…

more

established and disconnected, a locking issue causes mgd processes to hang in an unusable state. When the maximum number of mgd processes has been reached, no new logins are possible. This leads to the inability to manage the device and requires a power-cycle to recover. This issue can be monitored by checking for mgd processes in lockf state in the output of 'show system processes extensive': user@host> show system processes extensive | match mgd <pid> root 20 0 501M 4640K lockf 1 0:01 0.00% mgd If the system still can be accessed (either via the CLI or as root, which might still be possible as last resort as this won't invoke mgd), mgd processes in this state can be killed with 'request system process terminate <PID>' from the CLI or with 'kill -9 <PID>' from the shell. This issue affects: Junos OS: * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R2-S1, * 24.4 versions before 24.4R1-S3, 24.4R2; This issue does not affect Junos OS versions before 23.4R1; Junos OS Evolved: * 23.4 versions before 23.4R2-S5-EVO, * 24.2 versions before 24.2R2-S1-EVO, * 24.4 versions before 24.4R1-S3-EVO, 24.4R2-EVO. This issue does not affect Junos OS Evolved versions before 23.4R1-EVO;

CWE(s)

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-39554Same product: Juniper Junos
CVE-2025-52949Same product: Juniper Junos
CVE-2026-33793Same product: Juniper Junos
CVE-2023-28964Same product: Juniper Junos
CVE-2023-44204Same product: Juniper Junos
CVE-2024-30386Same product: Juniper Junos
CVE-2024-39564Same product: Juniper Junos
CVE-2023-0026Same product: Juniper Junos
CVE-2024-30395Same product: Juniper Junos
CVE-2026-21921Same product: Juniper Junos

Affected Assets

juniper
junos
23.4, 24.2, 24.4
juniper
junos os evolved
23.4, 24.2, 24.4

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SC-4 directly requires preventing unintended information transfer through shared resources, structurally blocking the concurrent unsynchronized access described by CWE-821.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require correct concurrency controls and synchronization primitives to prevent race conditions.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

finds

Security testing can detect synchronization flaws before production deployment.

prevents

Secure SDLC practices include concurrency and synchronization requirements that reduce race conditions.

prevents

Application security requirements can mandate proper locking and thread-safety controls.

prevents

Secure architecture principles address concurrent access and resource synchronization.

prevents

Secure coding standards directly require correct synchronization primitives and thread-safety.

none

Change management processes can introduce or miss synchronization fixes during updates.

References