A Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in the Routing Protocol Daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated attacker with an established BGP session to cause a Denial of Service (DoS). In a BGP multipath scenario, when one of the contributing routes is flapping often and rapidly, rpd may crash. As this crash depends on whether a route is a contributing route, and on the internal timing of the events triggered by the flap this vulnerability is outside the direct control of a potential attacker. This issue affects: Juniper Networks Junos OS 19.2 versions prior to 19.2R3-S6; 20.2 versions prior to 20.2R3-S4; 20.3 versions prior to 20.3R3-S3; 20.4 versions prior to 20.4R3-S4; 21.1 versions prior to 21.1R3; 21.2 versions prior to 21.2R2; 21.3 versions prior to 21.3R2. Juniper Networks Junos OS Evolved All versions prior to 20.4R3-S4-EVO; 21.1-EVO version 21.1R1-EVO and later versions; 21.2-EVO versions prior to 21.2R2-EVO; 21.3-EVO versions prior to 21.3R2-EVO. This issue does not affect: Juniper Networks Junos OS versions 19.2 versions prior to 19.2R2, 19.3R1 and above prior to 20.2R1. Juniper Networks Junos OS Evolved versions prior to 20.2R1-EVO.
| Software | From | Fixed in |
|---|---|---|
| juniper / junos | 19.2-r1 | 19.2-r1.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 | 19.2 | 19.2.x |
| juniper / junos | 19.2-r1-s3 | 19.2-r1-s3.x |
| juniper / junos | 19.2-r1-s4 | 19.2-r1-s4.x |
| juniper / junos | 20.2-r1 | 20.2-r1.x |
| juniper / junos | 19.2-r2 | 19.2-r2.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 | 19.2-r3 | 19.2-r3.x |
| juniper / junos | 19.2-r1-s5 | 19.2-r1-s5.x |
| juniper / junos | 20.3-r1 | 20.3-r1.x |
| juniper / junos | 19.2-r2-s1 | 19.2-r2-s1.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 | 20.2-r2 | 20.2-r2.x |
| juniper / junos | 20.2-r2-s1 | 20.2-r2-s1.x |
| juniper / junos | 19.2-r1-s6 | 19.2-r1-s6.x |
| juniper / junos | 20.4-r1 | 20.4-r1.x |
| juniper / junos | 20.2-r2-s2 | 20.2-r2-s2.x |
| juniper / junos | 20.4-r1-s1 | 20.4-r1-s1.x |
| juniper / junos | 20.2-r2-s3 | 20.2-r2-s3.x |
| juniper / junos | 20.3-r2 | 20.3-r2.x |
| juniper / junos | 21.1-r1 | 21.1-r1.x |
| juniper / junos | 20.4-r2 | 20.4-r2.x |
| juniper / junos | 20.3-r2-s1 | 20.3-r2-s1.x |
| juniper / junos | 20.2-r3 | 20.2-r3.x |
| juniper / junos | 20.2-r3-s1 | 20.2-r3-s1.x |
| juniper / junos | 19.2-r3-s2 | 19.2-r3-s2.x |
| juniper / junos | 21.2-r1 | 21.2-r1.x |
| juniper / junos | 20.4-r2-s1 | 20.4-r2-s1.x |
| juniper / junos | 21.1-r1-s1 | 21.1-r1-s1.x |
| juniper / junos | 20.3-r3 | 20.3-r3.x |
| juniper / junos | 20.2-r3-s2 | 20.2-r3-s2.x |
| juniper / junos | 19.2-r3-s3 | 19.2-r3-s3.x |
| juniper / junos | 21.2-r1-s1 | 21.2-r1-s1.x |
| juniper / junos | 21.1-r2 | 21.1-r2.x |
| juniper / junos | 20.4-r3 | 20.4-r3.x |
| juniper / junos | 19.2-r1-s7 | 19.2-r1-s7.x |
| juniper / junos | 19.2-r3-s4 | 19.2-r3-s4.x |
| juniper / junos | 20.2-r3-s3 | 20.2-r3-s3.x |
| juniper / junos | 20.3-r3-s1 | 20.3-r3-s1.x |
| juniper / junos | 21.3-r1 | 21.3-r1.x |
| juniper / junos | 20.4-r3-s1 | 20.4-r3-s1.x |
| juniper / junos | 20.4-r2-s2 | 20.4-r2-s2.x |
| juniper / junos | 21.1-r2-s1 | 21.1-r2-s1.x |
| juniper / junos | 21.2 | 21.2.x |
| juniper / junos | 21.1 | 21.1.x |
| juniper / junos | 20.4 | 20.4.x |
| juniper / junos | 20.3 | 20.3.x |
| juniper / junos | 20.2 | 20.2.x |
| juniper / junos | 21.1-r2-s2 | 21.1-r2-s2.x |
| juniper / junos | 21.2-r1-s2 | 21.2-r1-s2.x |
| juniper / junos | 21.3-r1-s1 | 21.3-r1-s1.x |
| juniper / junos | 21.3-r1-s2 | 21.3-r1-s2.x |
| juniper / junos | 19.2-r3-s5 | 19.2-r3-s5.x |
| juniper / junos | 19.2-r1-s8 | 19.2-r1-s8.x |
| juniper / junos | 20.3-r3-s2 | 20.3-r3-s2.x |
| juniper / junos | 19.2-r1-s9 | 19.2-r1-s9.x |
| juniper / junos | 20.3-r1-s2 | 20.3-r1-s2.x |
| juniper / junos | 20.4-r3-s2 | 20.4-r3-s2.x |
| juniper / junos | 20.4-r3-s3 | 20.4-r3-s3.x |
| juniper / junos | 21.3 | 21.3.x |
| juniper / junos_os_evolved | 20.4-r1 | 20.4-r1.x |
| juniper / junos_os_evolved | 21.1-r1 | 21.1-r1.x |
| juniper / junos_os_evolved | 21.1-r2 | 21.1-r2.x |
| juniper / junos_os_evolved | 21.1-r1-s1 | 21.1-r1-s1.x |
| juniper / junos_os_evolved | 21.2-r1 | 21.2-r1.x |
| juniper / junos_os_evolved | 21.2-r1-s1 | 21.2-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 | 20.4-r2 | 20.4-r2.x |
| juniper / junos_os_evolved | 20.4-r2-s1 | 20.4-r2-s1.x |
| juniper / junos_os_evolved | 20.4-r2-s2 | 20.4-r2-s2.x |
| juniper / junos_os_evolved | 20.4-r2-s3 | 20.4-r2-s3.x |
| juniper / junos_os_evolved | 20.4-r3 | 20.4-r3.x |
| juniper / junos_os_evolved | 20.4-r3-s1 | 20.4-r3-s1.x |
| juniper / junos_os_evolved | 21.3-r1 | 21.3-r1.x |
| juniper / junos_os_evolved | 20.4 | 20.4.x |
| juniper / junos_os_evolved | 21.2 | 21.2.x |
| juniper / junos_os_evolved | 21.2-r1-s2 | 21.2-r1-s2.x |
| juniper / junos_os_evolved | 21.3-r1-s1 | 21.3-r1-s1.x |
| juniper / junos_os_evolved | - | 20.4 |
| juniper / junos_os_evolved | 20.4-r3-s2 | 20.4-r3-s2.x |
| juniper / junos_os_evolved | 21.1-r3 | 21.1-r3.x |
| juniper / junos_os_evolved | 21.2-r3 | 21.2-r3.x |
| juniper / junos_os_evolved | 21.3 | 21.3.x |
| juniper / junos_os_evolved | 21.1-r3-s1 | 21.1-r3-s1.x |
| juniper / junos_os_evolved | 20.4-r3-s3 | 20.4-r3-s3.x |
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.