Vulnerability Database

346,508

Total vulnerabilities in the database

CVE-2021-0259 — juniper / junos

Improper Handling of Exceptional Conditions

Due to a vulnerability in DDoS protection in Juniper Networks Junos OS and Junos OS Evolved on QFX5K Series switches in a VXLAN configuration, instability might be experienced in the underlay network as a consequence of exceeding the default ddos-protection aggregate threshold. If an attacker on a client device on the overlay network sends a high volume of specific, legitimate traffic in the overlay network, due to an improperly detected DDoS violation, the leaf might not process certain L2 traffic, sent by spines in the underlay network. Continued receipt and processing of the high volume traffic will sustain the Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on QFX5K Series: 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R2-S8, 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R2-S4, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2; 20.3 versions prior to 20.3R1-S2, 20.3R2. Juniper Networks Junos OS Evolved on QFX5220: All versions prior to 20.3R2-EVO.

  • Published: Apr 22, 2021
  • Updated: Nov 16, 2025
  • CVE: CVE-2021-0259
  • Severity: High
  • Exploit:

CVSS v3:

  • Severity: High
  • Score: 7.4
  • AV:A/AC:L/PR:N/UI:N/S:C/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 17.3-r1 17.3-r1.x
juniper / junos 17.3-r2 17.3-r2.x
juniper / junos 17.3-r2-s2 17.3-r2-s2.x
juniper / junos 17.3-r3 17.3-r3.x
juniper / junos 17.3-r1-s4 17.3-r1-s4.x
juniper / junos 17.3-r3-s1 17.3-r3-s1.x
juniper / junos 17.3-r3-s2 17.3-r3-s2.x
juniper / junos 17.3-r2-s1 17.3-r2-s1.x
juniper / junos 17.3 17.3.x
juniper / junos 17.3-r3-s3 17.3-r3-s3.x
juniper / junos 17.3-r3-s4 17.3-r3-s4.x
juniper / junos 17.3-r3-s5 17.3-r3-s5.x
juniper / junos 17.3-r3-s6 17.3-r3-s6.x
juniper / junos 17.3-r2-s3 17.3-r2-s3.x
juniper / junos 17.3-r1-s1 17.3-r1-s1.x
juniper / junos 17.3-r2-s4 17.3-r2-s4.x
juniper / junos 17.3-r3-s7 17.3-r3-s7.x
juniper / junos 17.3-r2-s5 17.3-r2-s5.x
juniper / junos 17.3-r3-s8 17.3-r3-s8.x
juniper / junos 17.3-r3-s9 17.3-r3-s9.x
juniper / junos 17.3-r3-s10 17.3-r3-s10.x
juniper / junos 17.4-r3-s4 17.4-r3-s4.x
juniper / junos 17.4-r2-s11 17.4-r2-s11.x
juniper / junos 17.4-r3-s1 17.4-r3-s1.x
juniper / junos 17.4-r2-s9 17.4-r2-s9.x
juniper / junos 17.4-r2-s10 17.4-r2-s10.x
juniper / junos 17.4-r3-s2 17.4-r3-s2.x
juniper / junos 17.4-r3-s3 17.4-r3-s3.x
juniper / junos 17.4-r2-s8 17.4-r2-s8.x
juniper / junos 17.4-r2-s5 17.4-r2-s5.x
juniper / junos 17.4-r2-s6 17.4-r2-s6.x
juniper / junos 17.4-r2-s7 17.4-r2-s7.x
juniper / junos 17.4-r1-s7 17.4-r1-s7.x
juniper / junos 17.4-r1-s4 17.4-r1-s4.x
juniper / junos 17.4-r2-s3 17.4-r2-s3.x
juniper / junos 17.4-r2-s4 17.4-r2-s4.x
juniper / junos 17.4-r1-s6 17.4-r1-s6.x
juniper / junos 17.4-r1-s5 17.4-r1-s5.x
juniper / junos 17.4 17.4.x
juniper / junos 17.4-r1-s2 17.4-r1-s2.x
juniper / junos 17.4-r3 17.4-r3.x
juniper / junos 17.4-r2-s1 17.4-r2-s1.x
juniper / junos 17.4-r1-s3 17.4-r1-s3.x
juniper / junos 17.4-r2-s2 17.4-r2-s2.x
juniper / junos 17.4-r1-s1 17.4-r1-s1.x
juniper / junos 17.4-r1 17.4-r1.x
juniper / junos 17.4-r2 17.4-r2.x
juniper / junos 18.1-r1 18.1-r1.x
juniper / junos 18.1-r3 18.1-r3.x
juniper / junos 18.1-r2 18.1-r2.x
juniper / junos 18.1-r2-s2 18.1-r2-s2.x
juniper / junos 18.1-r3-s4 18.1-r3-s4.x
juniper / junos 18.1-r3-s3 18.1-r3-s3.x
juniper / junos 18.1-r3-s2 18.1-r3-s2.x
juniper / junos 18.1 18.1.x
juniper / junos 18.1-r2-s1 18.1-r2-s1.x
juniper / junos 18.1-r2-s4 18.1-r2-s4.x
juniper / junos 18.1-r3-s1 18.1-r3-s1.x
juniper / junos 18.1-r3-s5 18.1-r3-s5.x
juniper / junos 18.1-r3-s6 18.1-r3-s6.x
juniper / junos 18.1-r3-s7 18.1-r3-s7.x
juniper / junos 18.1-r3-s8 18.1-r3-s8.x
juniper / junos 18.1-r3-s9 18.1-r3-s9.x
juniper / junos 18.1-r3-s10 18.1-r3-s10.x
juniper / junos 18.1-r3-s12 18.1-r3-s12.x
juniper / junos 18.1-r3-s11 18.1-r3-s11.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 18.2-r2-s7 18.2-r2-s7.x
juniper / junos 18.2-r3-s7 18.2-r3-s7.x
juniper / junos 18.2-r3-s5 18.2-r3-s5.x
juniper / junos 18.2-r3-s4 18.2-r3-s4.x
juniper / junos 18.2-r3-s3 18.2-r3-s3.x
juniper / junos 18.2-r3-s2 18.2-r3-s2.x
juniper / junos 18.2-r3-s1 18.2-r3-s1.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 18.2-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 18.2-r3 18.2-r3.x
juniper / junos 18.2-r1 18.2-r1.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 18.2 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-r1-s2 18.3-r1-s2.x
juniper / junos 18.3 18.3.x
juniper / junos 18.3-r2 18.3-r2.x
juniper / junos 18.3-r1 18.3-r1.x
juniper / junos 18.3-r1-s4 18.3-r1-s4.x
juniper / junos 18.3-r1-s3 18.3-r1-s3.x
juniper / junos 18.3-r1-s5 18.3-r1-s5.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 18.3-r1-s6 18.3-r1-s6.x
juniper / junos 18.3-r3 18.3-r3.x
juniper / junos 18.3-r2-s3 18.3-r2-s3.x
juniper / junos 18.3-r3-s1 18.3-r3-s1.x
juniper / junos 18.3-r3-s3 18.3-r3-s3.x
juniper / junos 18.3-r2-s4 18.3-r2-s4.x
juniper / junos 18.3-r3-s2 18.3-r3-s2.x
juniper / junos 18.3-r3-s4 18.3-r3-s4.x
juniper / junos 18.4-r1-s7 18.4-r1-s7.x
juniper / junos 18.4-r3-s5 18.4-r3-s5.x
juniper / junos 18.4-r2-s5 18.4-r2-s5.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 18.4-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 18.4-r3 18.4-r3.x
juniper / junos 18.4-r2-s3 18.4-r2-s3.x
juniper / junos 18.4-r1-s6 18.4-r1-s6.x
juniper / junos 18.4-r2-s2 18.4-r2-s2.x
juniper / junos 18.4-r2-s1 18.4-r2-s1.x
juniper / junos 18.4-r1-s1 18.4-r1-s1.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 18.4-r2 18.4-r2.x
juniper / junos 18.4-r1-s5 18.4-r1-s5.x
juniper / junos 18.4-r1 18.4-r1.x
juniper / junos 18.4 18.4.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 19.1-r1 19.1-r1.x
juniper / junos 19.1 19.1.x
juniper / junos 19.1-r1-s4 19.1-r1-s4.x
juniper / junos 19.1-r2 19.1-r2.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 19.1-r3-s2 19.1-r3-s2.x
juniper / junos 19.1-r3-s3 19.1-r3-s3.x
juniper / junos 19.1-r1-s5 19.1-r1-s5.x
juniper / junos 19.2-r2-s1 19.2-r2-s1.x
juniper / junos 19.2-r3 19.2-r3.x
juniper / junos 19.2-r1-s5 19.2-r1-s5.x
juniper / junos 19.2-r3-s1 19.2-r3-s1.x
juniper / junos 19.2-r2 19.2-r2.x
juniper / junos 19.2-r1-s4 19.2-r1-s4.x
juniper / junos 19.2 19.2.x
juniper / junos 19.2-r1-s3 19.2-r1-s3.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-r1 19.2-r1.x
juniper / junos 19.3 19.3.x
juniper / junos 19.3-r1 19.3-r1.x
juniper / junos 19.3-r2-s2 19.3-r2-s2.x
juniper / junos 19.3-r2 19.3-r2.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 19.3-r2-s3 19.3-r2-s3.x
juniper / junos 19.3-r2-s4 19.3-r2-s4.x
juniper / junos 19.3-r3-s1 19.3-r3-s1.x
juniper / junos 19.3-r2-s5 19.3-r2-s5.x
juniper / junos 19.3-r3 19.3-r3.x
juniper / junos 19.4-r3 19.4-r3.x
juniper / junos 19.4-r1-s3 19.4-r1-s3.x
juniper / junos 19.4-r2-s3 19.4-r2-s3.x
juniper / junos 19.4-r2-s2 19.4-r2-s2.x
juniper / junos 19.4-r2 19.4-r2.x
juniper / junos 19.4-r2-s1 19.4-r2-s1.x
juniper / junos 19.4-r1-s2 19.4-r1-s2.x
juniper / junos 19.4-r1-s1 19.4-r1-s1.x
juniper / junos 19.4-r1 19.4-r1.x
juniper / junos 20.1-r1 20.1-r1.x
juniper / junos 20.1-r1-s1 20.1-r1-s1.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 20.1-r1-s4 20.1-r1-s4.x
juniper / junos 20.2-r1-s3 20.2-r1-s3.x
juniper / junos 20.2-r1 20.2-r1.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 20.3-r1-s1 20.3-r1-s1.x
juniper / junos 20.3-r1 20.3-r1.x
juniper / junos_os_evolved 18.3-r1 18.3-r1.x
juniper / junos_os_evolved 19.1-r1 19.1-r1.x
juniper / junos_os_evolved 19.1-r2 19.1-r2.x
juniper / junos_os_evolved 19.2-r1 19.2-r1.x
juniper / junos_os_evolved 19.2-r2 19.2-r2.x
juniper / junos_os_evolved 19.3-r1 19.3-r1.x
juniper / junos_os_evolved 19.3-r2 19.3-r2.x
juniper / junos_os_evolved 20.1-r1 20.1-r1.x
juniper / junos_os_evolved 20.1-r2 20.1-r2.x
juniper / junos_os_evolved 20.2-r2 20.2-r2.x
juniper / junos_os_evolved 20.2-r1 20.2-r1.x
juniper / junos_os_evolved 20.3-r1 20.3-r1.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.