CVE-2026-57022 in Junos OS
Summary
by MITRE • 07/10/2026
An Improper Check for Unusual or Exceptional Conditions vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on MX with SPC3 and SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).
When an affected device initiates a TCP connection to an attacker-controlled system that responds with a specific packet, this causes a PFE crash and restart, which affects all services until the system has automatically recovered. This issue can happen among others in the following scenarios: ALG, SSL proxy, UTM, RTLOG, AppQoE probing, AAMW, ICAP, URL filtering.
This issue affects Junos OS on MX Series with SPC3, SRX5k Series with SPC3, SRX1600 Series, SRX2300 Series, SRX4000 Series, and vSRX Series:
* all versions before 23.2R2-S4, * 23.4 versions before 23.4R2-S5, * 24.2 versions before 24.2R2.
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Analysis
by VulDB Data Team • 07/10/2026
This vulnerability represents a critical improper check for unusual or exceptional conditions flaw within the Packet Forwarding Engine of Juniper Networks Junos OS implementations. The weakness manifests specifically in devices utilizing SPC3 hardware components where the PFE fails to properly validate incoming TCP connection responses from attacker-controlled systems. This fundamental design oversight creates a condition where legitimate network traffic processing can be interrupted through carefully crafted malicious packets that trigger unexpected system behavior.
The technical mechanism involves a specific sequence where an attacker can establish a TCP connection to a controlled system and receive back a packet with particular characteristics that cause the PFE to crash and restart automatically. This process affects all network services since the PFE is responsible for packet forwarding operations across the entire device infrastructure. The vulnerability operates under CWE-252 which specifically addresses improper checks for unusual conditions, making it particularly dangerous as it can be exploited without authentication requirements and from any network location that can reach the target device.
The operational impact extends beyond simple service disruption to encompass complete system unavailability during the recovery process which typically requires several minutes for automatic restoration. This affects critical network infrastructure components including ALG functionality for application layer gateways, SSL proxy services that handle encrypted traffic inspection, UTM capabilities for unified threat management, RTLOG operations for real-time logging, AppQoE probing for application quality of experience monitoring, AAMW for application availability monitoring, ICAP protocol handling for content filtering, and URL filtering operations that control web access policies.
The vulnerability affects multiple hardware series within Juniper's product portfolio including MX Series devices with SPC3 line cards, SRX5k Series with SPC3 hardware, SRX1600 Series platforms, SRX2300 Series equipment, SRX4000 Series systems, and vSRX virtualized implementations. The affected software versions span across different release branches where the issue was present in all versions prior to 23.2R2-S4, within 23.4 releases before 23.4R2-S5, and in 24.2 versions before 24.2R2. This widespread impact across multiple product lines demonstrates the fundamental nature of the flaw in the PFE processing logic.
Security researchers have categorized this vulnerability under ATT&CK technique T1498 which covers Network Denial of Service attacks, specifically focusing on resource exhaustion and system instability. The attack vector requires only network connectivity to the target device making it particularly dangerous for devices that are exposed to untrusted networks or internet-facing services. This vulnerability represents a classic example of how improper input validation can lead to complete system compromise through denial-of-service mechanisms.
Mitigation strategies primarily involve applying the appropriate software patches and firmware updates provided by Juniper Networks to address the specific PFE processing logic flaws. Network administrators should prioritize patching affected devices, particularly those running versions in the specified vulnerable ranges, and implement network segmentation to reduce exposure. Additionally, monitoring for unusual TCP connection patterns and implementing rate limiting on suspicious traffic can provide additional defensive layers against exploitation attempts.
The vulnerability highlights important considerations for network security architecture including the need for robust input validation in packet processing engines, proper error handling mechanisms, and comprehensive testing of edge cases that could lead to system instability. Organizations should conduct thorough risk assessments to identify all affected devices within their network infrastructure and implement appropriate monitoring solutions to detect potential exploitation attempts before they can cause service disruption.
This issue underscores the critical importance of maintaining current security patches for network infrastructure components, particularly those handling core forwarding functions where improper validation can lead to complete system compromise through denial-of-service attacks. The vulnerability demonstrates how seemingly minor flaws in system processing logic can have major operational consequences across entire network infrastructures that rely on stable packet forwarding capabilities for their operations.