Vulnerability Database

346,508

Total vulnerabilities in the database

CVE-2021-31362 — juniper / junos

Protection Mechanism Failure

A Protection Mechanism Failure vulnerability in RPD (routing protocol daemon) of Juniper Networks Junos OS and Junos OS Evolved allows an adjacent unauthenticated attacker to cause established IS-IS adjacencies to go down by sending a spoofed hello PDU leading to a Denial of Service (DoS) condition. Continued receipted of these spoofed PDUs will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS All versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S7; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R3-S3; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R3; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2. Juniper Networks Junos OS Evolved All versions prior to 20.4R2-EVO; 21.1 versions prior to 21.1R2-EVO.

  • Published: Oct 19, 2021
  • Updated: Nov 16, 2025
  • CVE: CVE-2021-31362
  • Severity: Medium
  • Exploit:

CVSS v3:

  • Severity: Medium
  • Score: 6.5
  • AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v2:

  • Severity: Low
  • Score: 3.3
  • AV:A/AC:L/Au:N/C:N/I:N/A:P

CWEs:

Software From Fixed in
juniper / junos 18.2-r1 18.2-r1.x
juniper / junos 18.2 18.2.x
juniper / junos 18.2-r2-s1 18.2-r2-s1.x
juniper / junos 18.2-r2-s2 18.2-r2-s2.x
juniper / junos 18.2-r1-s3 18.2-r1-s3.x
juniper / junos 18.3-r1-s1 18.3-r1-s1.x
juniper / junos 18.3-r2 18.3-r2.x
juniper / junos 18.3-r1 18.3-r1.x
juniper / junos 18.4-r1 18.4-r1.x
juniper / junos 18.3-r1-s2 18.3-r1-s2.x
juniper / junos 18.3 18.3.x
juniper / junos 18.4 18.4.x
juniper / junos 18.4-r1-s1 18.4-r1-s1.x
juniper / junos 18.3-r1-s3 18.3-r1-s3.x
juniper / junos 18.2-r2-s3 18.2-r2-s3.x
juniper / junos 18.2-r2-s4 18.2-r2-s4.x
juniper / junos 18.3-r1-s4 18.3-r1-s4.x
juniper / junos 18.2-r1-s4 18.2-r1-s4.x
juniper / junos 18.2-r1-s5 18.2-r1-s5.x
juniper / junos 18.2-r2 18.2-r2.x
juniper / junos - 18.1.x
juniper / junos 18.4-r1-s3 18.4-r1-s3.x
juniper / junos 18.4-r1-s4 18.4-r1-s4.x
juniper / junos 18.4-r1-s2 18.4-r1-s2.x
juniper / junos 19.1-r1 19.1-r1.x
juniper / junos 19.1 19.1.x
juniper / junos 19.2-r1 19.2-r1.x
juniper / junos 18.4-r2 18.4-r2.x
juniper / junos 18.2-r3 18.2-r3.x
juniper / junos 19.1-r1-s1 19.1-r1-s1.x
juniper / junos 19.1-r1-s3 19.1-r1-s3.x
juniper / junos 19.1-r1-s2 19.1-r1-s2.x
juniper / junos 18.2-r2-s5 18.2-r2-s5.x
juniper / junos 18.2-r2-s6 18.2-r2-s6.x
juniper / junos 18.4-r1-s5 18.4-r1-s5.x
juniper / junos 19.2-r1-s1 19.2-r1-s1.x
juniper / junos 19.2-r1-s2 19.2-r1-s2.x
juniper / junos 18.3-r1-s5 18.3-r1-s5.x
juniper / junos 18.2-r3-s1 18.2-r3-s1.x
juniper / junos 18.3-r2-s1 18.3-r2-s1.x
juniper / junos 18.3-r2-s2 18.3-r2-s2.x
juniper / junos 18.4-r2-s1 18.4-r2-s1.x
juniper / junos 19.3 19.3.x
juniper / junos 19.3-r1 19.3-r1.x
juniper / junos 19.2 19.2.x
juniper / junos 18.4-r2-s2 18.4-r2-s2.x
juniper / junos 18.3-r1-s6 18.3-r1-s6.x
juniper / junos 18.2-r3-s2 18.2-r3-s2.x
juniper / junos 19.2-r1-s3 19.2-r1-s3.x
juniper / junos 18.3-r3 18.3-r3.x
juniper / junos 19.4-r1 19.4-r1.x
juniper / junos 19.3-r2 19.3-r2.x
juniper / junos 19.1-r2 19.1-r2.x
juniper / junos 18.4-r3 18.4-r3.x
juniper / junos 18.4-r2-s3 18.4-r2-s3.x
juniper / junos 18.3-r3-s1 18.3-r3-s1.x
juniper / junos 19.3-r2-s1 19.3-r2-s1.x
juniper / junos 19.3-r1-s1 19.3-r1-s1.x
juniper / junos 19.2-r1-s4 19.2-r1-s4.x
juniper / junos 20.1-r1 20.1-r1.x
juniper / junos 19.4-r1-s1 19.4-r1-s1.x
juniper / junos 19.3-r2-s2 19.3-r2-s2.x
juniper / junos 19.1-r1-s4 19.1-r1-s4.x
juniper / junos 18.4-r1-s6 18.4-r1-s6.x
juniper / junos 18.3-r2-s3 18.3-r2-s3.x
juniper / junos 18.2-r3-s3 18.2-r3-s3.x
juniper / junos 18.2-r3-s4 18.2-r3-s4.x
juniper / junos 18.4-r3-s2 18.4-r3-s2.x
juniper / junos 18.4-r3-s1 18.4-r3-s1.x
juniper / junos 18.4-r2-s4 18.4-r2-s4.x
juniper / junos 19.1-r2-s1 19.1-r2-s1.x
juniper / junos 19.1-r3 19.1-r3.x
juniper / junos 19.1-r3-s1 19.1-r3-s1.x
juniper / junos 19.4-r1-s2 19.4-r1-s2.x
juniper / junos 20.1-r1-s1 20.1-r1-s1.x
juniper / junos 20.2-r1 20.2-r1.x
juniper / junos 20.1-r1-s2 20.1-r1-s2.x
juniper / junos 20.1-r1-s3 20.1-r1-s3.x
juniper / junos 19.4-r2 19.4-r2.x
juniper / junos 19.4-r2-s1 19.4-r2-s1.x
juniper / junos 19.3-r2-s3 19.3-r2-s3.x
juniper / junos 19.1-r3-s2 19.1-r3-s2.x
juniper / junos 18.4-r3-s3 18.4-r3-s3.x
juniper / junos 18.4-r3-s4 18.4-r3-s4.x
juniper / junos 18.2-r3-s5 18.2-r3-s5.x
juniper / junos 18.3-r3-s2 18.3-r3-s2.x
juniper / junos 19.2-r2 19.2-r2.x
juniper / junos 18.3-r2-s4 18.3-r2-s4.x
juniper / junos 19.3-r2-s4 19.3-r2-s4.x
juniper / junos 18.3-r3-s3 18.3-r3-s3.x
juniper / junos 20.2-r1-s1 20.2-r1-s1.x
juniper / junos 20.2-r1-s2 20.2-r1-s2.x
juniper / junos 19.4-r2-s2 19.4-r2-s2.x
juniper / junos 19.2-r3 19.2-r3.x
juniper / junos 18.4-r3-s5 18.4-r3-s5.x
juniper / junos 19.4-r3 19.4-r3.x
juniper / junos 19.3-r2-s5 19.3-r2-s5.x
juniper / junos 19.3-r3 19.3-r3.x
juniper / junos 19.2-r1-s5 19.2-r1-s5.x
juniper / junos 19.1-r3-s3 19.1-r3-s3.x
juniper / junos 18.4-r2-s5 18.4-r2-s5.x
juniper / junos 18.4-r2-s6 18.4-r2-s6.x
juniper / junos 19.1-r1-s5 19.1-r1-s5.x
juniper / junos 18.4-r1-s7 18.4-r1-s7.x
juniper / junos 20.3-r1 20.3-r1.x
juniper / junos 18.2-r2-s7 18.2-r2-s7.x
juniper / junos 19.2-r2-s1 19.2-r2-s1.x
juniper / junos 18.2-r3-s6 18.2-r3-s6.x
juniper / junos 18.2-r1-s2 18.2-r1-s2.x
juniper / junos 20.1-r1-s4 20.1-r1-s4.x
juniper / junos 19.1-r3-s4 19.1-r3-s4.x
juniper / junos 18.4-r3-s6 18.4-r3-s6.x
juniper / junos 18.3-r3-s4 18.3-r3-s4.x
juniper / junos 18.2-r3-s7 18.2-r3-s7.x
juniper / junos 20.3-r1-s1 20.3-r1-s1.x
juniper / junos 20.2-r1-s3 20.2-r1-s3.x
juniper / junos 19.2-r3-s1 19.2-r3-s1.x
juniper / junos 18.4-r3-s7 18.4-r3-s7.x
juniper / junos 19.4-r3-s1 19.4-r3-s1.x
juniper / junos 19.4-r2-s3 19.4-r2-s3.x
juniper / junos 20.2-r2 20.2-r2.x
juniper / junos 20.2-r2-s1 20.2-r2-s1.x
juniper / junos 19.4-r1-s3 19.4-r1-s3.x
juniper / junos 19.2-r1-s6 19.2-r1-s6.x
juniper / junos 19.1-r2-s2 19.1-r2-s2.x
juniper / junos 20.4-r1 20.4-r1.x
juniper / junos 20.2-r2-s2 20.2-r2-s2.x
juniper / junos 20.1-r2 20.1-r2.x
juniper / junos 20.1-r2-s1 20.1-r2-s1.x
juniper / junos_os_evolved 20.4-r1 20.4-r1.x
juniper / junos 20.4-r1-s1 20.4-r1-s1.x
juniper / junos 19.1-r1-s6 19.1-r1-s6.x
juniper / junos 20.2-r2-s3 20.2-r2-s3.x
juniper / junos 20.3-r2 20.3-r2.x
juniper / junos 19.3-r3-s1 19.3-r3-s1.x
juniper / junos 18.4-r2-s7 18.4-r2-s7.x
juniper / junos 20.3-r2-s1 20.3-r2-s1.x
juniper / junos 19.4-r3-s2 19.4-r3-s2.x
juniper / junos 19.2-r3-s2 19.2-r3-s2.x
juniper / junos 18.4-r2-s8 18.4-r2-s8.x
juniper / junos 20.1-r2-s2 20.1-r2-s2.x
juniper / junos 19.1-r3-s5 19.1-r3-s5.x
juniper / junos 18.4-r3-s8 18.4-r3-s8.x
juniper / junos_os_evolved 21.1-r1 21.1-r1.x
juniper / junos 19.4-r2-s4 19.4-r2-s4.x
juniper / junos_os_evolved 21.1-r1-s1 21.1-r1-s1.x
juniper / junos_os_evolved 21.1 21.1.x
juniper / junos_os_evolved 20.4-r1-s1 20.4-r1-s1.x
juniper / junos_os_evolved 20.4-r1-s2 20.4-r1-s2.x
juniper / junos_os_evolved - 20.3.x
juniper / junos 19.4-r1-s4 19.4-r1-s4.x
juniper / junos 19.1-r3-s6 19.1-r3-s6.x

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.