CVE-2026-57026 in Junos OS
Summary
by MITRE • 07/10/2026
An Improper Validation of Syntactic Correctness of Input vulnerability in the SIP plugin of Juniper Networks Junos OS on MX Series with SPC3 and SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).If the SIP ALG is enabled on an affected device, the processing of a malformed SIP invite packet will cause a flow processing daemon (flowd) crash and restart. This leads to a complete service outage until the system has automatically recovered.
This issue affects Junos OS on MX Series with SPC3 and SRX Series:
* all versions before 23.2R2-S7, * 23.4 versions before 23.4R2-S8, * 24.2 versions before 24.2R2-S5, * 24.4 versions before 24.4R2-S4, * 25.2 versions before 25.2R2, * 25.4 versions before 25.4R1-S2.
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Analysis
by VulDB Data Team • 07/10/2026
This vulnerability represents a critical denial-of-service weakness in Juniper Networks Junos OS affecting specific hardware platforms including MX Series with SPC3 and SRX Series devices. The flaw exists within the Session Initiation Protocol application layer gateway functionality that processes SIP traffic, specifically when handling malformed SIP invite packets. This issue manifests as an improper validation of syntactic correctness of input where the system fails to adequately sanitize or validate incoming SIP packet structures before processing them through the flowd daemon.
The technical exploitation occurs when an unauthenticated attacker sends maliciously crafted SIP invite packets to a vulnerable device with SIP ALG enabled. The vulnerability stems from insufficient input validation mechanisms that allow malformed data to bypass initial screening and reach the core processing components. When the flowd daemon encounters these malformed packets, it crashes due to improper handling of unexpected packet structures, leading to complete service disruption. This behavior aligns with CWE-20, which describes improper input validation vulnerabilities that can lead to system instability and denial-of-service conditions.
The operational impact extends beyond simple service interruption as the affected systems experience complete service outage until automatic recovery mechanisms restore normal operation. This downtime can severely affect voice communication services, video conferencing capabilities, and any other SIP-based applications relying on these network devices. The vulnerability affects multiple software version streams including 23.2R2-S7, 23.4R2-S8, 24.2R2-S5, 24.4R2-S4, 25.2R2, and 25.4R1-S2, indicating a widespread issue across the Junos OS release cycle that requires immediate remediation across affected deployments.
Security practitioners should note this vulnerability's alignment with ATT&CK technique T1499.004 which covers network disruption attacks through service availability compromise. The attack vector requires only network-based access without authentication requirements, making it particularly dangerous for devices exposed to untrusted networks or internet-facing interfaces. Organizations should implement immediate mitigations including disabling SIP ALG functionality on affected devices, implementing network segmentation to limit exposure, and applying the relevant software patches from Juniper. The vulnerability demonstrates how application layer gateways can become attack vectors when insufficient validation occurs at multiple processing layers within the network infrastructure stack.
This issue highlights critical security considerations for enterprise voice infrastructure where network devices must maintain high availability while processing complex protocol traffic. Network administrators should conduct comprehensive inventory assessments to identify all affected devices and implement monitoring solutions to detect potential exploitation attempts. The vulnerability also underscores the importance of robust input validation practices in network security appliances, particularly those handling real-time communication protocols that require continuous availability for business operations.