Juniper Junos Null Pointer Reference DoS Vulnerability (CVE-2026-21901) Security Bulletin

Vulnerability Overview Vulnerability Name: Juniper Junos - Null pointer reference (CVE-2026-21901) Severity: Medium (6.7 / 10) CVSS v4 Base Metrics: - Attack Vector: Local - Attack Complexity: Low - Attack Requirements: None - Privileges Required: High - User Interaction: None - Confidentiality Impact: None - Integrity Impact: None - Availability Impact: High - Subsequent System Impacts: - Confidentiality Impact: None - Integrity Impact: None - Availability Impact: Low Affected Products Affected Products: - Junos running on MX (Juniper) - Junos running on cRPD (Juniper) - Junos running on vSRX (Juniper) Affected Versions: - MX: 23.4R1.9 - cRPD: 23.3R1.13 - vSRX: 23.4R2-S5.5 Fixed Versions: - MX: 23.4R2-S8 - cRPD: 23.2R2-S7 - vSRX: 23.4R2-S8 Remediation Recommended Remediation Code Fix: Temporary Solution: - Avoid using the configuration parameter until a patch is available. Official Remediation Patch: - Upgrade to appropriate versions: - Junos OS: 22.3R3-S5, 22.4R3-S10, 23.2R2-S7, 23.4R2-S8, 24.2R1, and all subsequent versions. - Junos OS Evolved: 23.2R2-S7-EVO, 23.4R2-S8-EVO, 24.2R1-EVO, and all subsequent versions. Mitigations: - No direct mitigations available. - The following measures can prevent malicious exploitation: - Use access lists or firewall filters to restrict CLI access to trusted hosts and administrators only. - Use command authorization to restrict access to configuration mode to trusted administrators only. Proof of Concept (POC) 1. Access the JunOS device with administrator privileges. 2. Enter configuration mode. 3. Add the following configuration: 4. Save the configuration. 5. Disable said configuration: 6. Execute or 7. Observe that the process exhibits a SIGSEGV. This vulnerability can be reliably reproduced across multiple JunOS variants. Triggering the denial-of-service condition requires only the minimal configuration changes listed above, with no additional exploit code needed. References Juniper Support Portal Juniper Security Research NVD Vulnerability Database Contributors Pierre EMERIAUD from Orange group Orange CERT-CC at Orange group Timeline Report Date: November 10, 2025 Fix Date: July 8, 2026

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Juniper Junos Null Pointer Reference DoS Vulnerability (CVE-2026-21901) Security Bulletin

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