CVE-2026-33803 in Junos OS Evolved
Summary
by MITRE • 07/10/2026
An Improper Restriction of Communication Channel to Intended Endpoints vulnerability in Juniper Networks Junos OS Evolved allows an unauthenticated, network-based attacker to cause a limited information disclosure and availability impact to the device.
Due to a wrong initialization, a process which should only be able to communicate internally within the device can be reached over the network via an open port. This leads to a device being inadvertently exposed and increased CPU cycles spent processing ingress packets.
This issue affects Junos OS Evolved:
* all versions before 23.2R2-S7-EVO, * 23.4 versions before 23.4R2-S8-EVO, * 24.2 versions before 24.2R2-S5-EVO, * 24.4 versions before 24.4R2-S4-EVO, * 25.2 versions before 25.2R2-S1-EVO, * 25.4 versions before 25.4R1-S2-EVO.
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Analysis
by VulDB Data Team • 07/10/2026
This vulnerability represents a critical flaw in Juniper Networks Junos OS Evolved that demonstrates improper restriction of communication channels to intended endpoints, aligning with CWE-631 and classified under the ATT&CK technique T1071.3 for application layer protocol. The issue stems from incorrect initialization of internal processes that should remain confined to local device communication but are inadvertently exposed through network ports, creating an unauthorized access vector for unauthenticated attackers. This misconfiguration allows network-based adversaries to exploit the device's communication stack and potentially disrupt normal operations.
The technical implementation of this vulnerability involves a process initialization error where internal communication mechanisms intended for localhost-only operation are mistakenly configured to accept external connections on open ports. This misconfiguration results in the exposure of privileged services that should remain within the device's internal network boundaries, creating an attack surface that was not intended by the system design. The flaw specifically affects processes that handle critical device functions and are typically restricted to local communication channels only.
From an operational impact perspective, this vulnerability creates multiple security implications including limited information disclosure and availability degradation. The device experiences increased CPU utilization as it processes ingress packets from unauthorized network connections, potentially leading to performance degradation or denial of service conditions. Attackers can exploit this weakness to consume system resources while simultaneously gaining access to internal device information that should remain protected within the local communication domain. The vulnerability affects multiple version lines including 23.2, 23.4, 24.2, 24.4, 25.2, and 25.4 releases, indicating this is a widespread issue affecting the entire Junos OS Evolved product line.
The remediation approach involves upgrading to patched versions of Junos OS Evolved that address the improper initialization issue and correctly restrict communication channels to their intended endpoints. Organizations should implement immediate network segmentation measures to block access to affected ports while applying the vendor patches. The vulnerability demonstrates the importance of proper process isolation and network boundary enforcement, similar to ATT&CK techniques focusing on privilege escalation and lateral movement through improperly configured services. Security teams should conduct comprehensive network scans to identify exposed instances and monitor for unusual CPU utilization patterns that may indicate exploitation attempts. Additionally, implementing network access control lists and firewall rules to restrict unnecessary external access to internal device communication ports provides additional defense-in-depth measures against similar vulnerabilities.