CVE-2026-21914 is an improper locking vulnerability classified under CWE-667, found in the GPRS Tunnelling Protocol (GTP) plugin of Juniper Networks Junos OS running on SRX Series devices. The flaw arises when the device receives a specially crafted GTP Modify Bearer Request message. This malformed message causes the system to acquire a lock that is never released, effectively blocking other threads from obtaining the same lock. As a result, the system experiences a watchdog timeout, triggering a crash and automatic restart of the Flexible PIC Concentrator (FPC) module. This crash leads to a denial-of-service (DoS) condition, causing a complete outage of traffic passing through the affected device until it recovers. The vulnerability affects multiple Junos OS versions before the following patched releases: 22.4R3-S8, 23.2R2-S5, 23.4R2-S6, 24.2R2-S3, 24.4R2-S2, and 25.2R1-S1/25.2R2. The vulnerability is remotely exploitable without authentication or user interaction, increasing its risk profile. The CVSS v3.1 base score is 7.5, reflecting high severity due to the ease of exploitation and significant impact on availability. No known exploits have been reported in the wild to date, but the potential for disruption in critical network environments is substantial. Juniper SRX Series devices are widely deployed in enterprise and service provider networks, making this vulnerability a critical concern for network reliability and uptime.

The primary impact of CVE-2026-21914 is a denial-of-service condition that causes the affected Juniper SRX device to crash and restart, resulting in a complete traffic outage. For European organizations, this can lead to significant network downtime, affecting business continuity, especially for enterprises and service providers relying on SRX Series devices for firewalling, routing, and VPN services. Critical sectors such as telecommunications, finance, government, and energy could experience service disruptions, potentially impacting end-users and customers. The lack of authentication requirement means attackers can exploit this vulnerability remotely, increasing the risk of widespread attacks. Additionally, the automatic restart may temporarily restore service but does not prevent repeated exploitation, potentially leading to persistent outages. This vulnerability could also be leveraged as part of a larger attack campaign to degrade network infrastructure or as a distraction while other attacks are conducted. The disruption of network traffic could affect data flows across European borders, impacting interconnected systems and services.

European organizations should urgently apply the patches provided by Juniper for the affected Junos OS versions, upgrading to the fixed releases: 22.4R3-S8 or later, 23.2R2-S5 or later, 23.4R2-S6 or later, 24.2R2-S3 or later, 24.4R2-S2 or later, and 25.2R1-S1/25.2R2 or later. Until patches are applied, network administrators should implement strict filtering of GTP traffic at network boundaries to block malformed or suspicious GTP Modify Bearer Request messages, potentially using deep packet inspection capabilities of existing security devices. Monitoring network traffic for unusual GTP message patterns can help detect attempted exploitation. Deploy rate limiting on GTP traffic to reduce the risk of DoS attacks exploiting this vulnerability. Network segmentation should be enforced to isolate critical SRX devices from untrusted networks. Additionally, ensure that device management interfaces are not exposed to untrusted networks to reduce attack surface. Regularly review and update incident response plans to include scenarios involving network device DoS. Finally, maintain up-to-date backups and ensure rapid recovery procedures are in place to minimize downtime in case of exploitation.