Vulnerability Database

346,508

Total vulnerabilities in the database

CVE-2021-0264 — juniper / junos

Improper Handling of Exceptional Conditions

A vulnerability in the processing of traffic matching a firewall filter containing a syslog action in Juniper Networks Junos OS on MX Series with MPC10/MPC11 cards installed, PTX10003 and PTX10008 Series devices, will cause the line card to crash and restart, creating a Denial of Service (DoS). Continued receipt and processing of packets matching the firewall filter can create a sustained Denial of Service (DoS) condition. When traffic hits the firewall filter, configured on lo0 or any physical interface on the line card, containing a term with a syslog action (e.g. 'term <name> then syslog'), the affected line card will crash and restart, impacting traffic processing through the ports of the line card. This issue only affects MX Series routers with MPC10 or MPC11 line cards, and PTX10003 or PTX10008 Series packet transport routers. No other platforms or models of line cards are affected by this issue. Note: This issue has also been identified and described in technical service bulletin TSB17931 (login required). This issue affects: Juniper Networks Junos OS on MX Series: 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R3-S2; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R2-S2, 20.2R3; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2. Juniper Networks Junos OS Evolved on PTX10003, PTX10008: All versions prior to 20.4R2-EVO. This issue does not affect Juniper Networks Junos OS versions prior to 19.3R1.

  • Published: Apr 22, 2021
  • Updated: Nov 16, 2025
  • CVE: CVE-2021-0264
  • Severity: Medium
  • Exploit:

CVSS v3:

  • Severity: Medium
  • Score: 5.9
  • AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v2:

  • Severity: Medium
  • Score: 5
  • AV:N/AC:L/Au:N/C:N/I:N/A:P
Software From Fixed in
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-s2 19.3-r2-s2.x
juniper / junos 19.3 19.3.x
juniper / junos 19.3-r1 19.3-r1.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-r2-s5 19.3-r2-s5.x
juniper / junos 19.3-r3 19.3-r3.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-r2-s2 19.4-r2-s2.x
juniper / junos 19.4-r3 19.4-r3.x
juniper / junos 19.4-r3-s1 19.4-r3-s1.x
juniper / junos 19.4-r1-s1 19.4-r1-s1.x
juniper / junos 19.4-r1 19.4-r1.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 20.1-r1 20.1-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 20.1-r2 20.1-r2.x
juniper / junos 20.1-r2-s1 20.1-r2-s1.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-r2 20.2-r2.x
juniper / junos 20.2-r2-s1 20.2-r2-s1.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 20.2-r1 20.2-r1.x
juniper / junos 20.3-r2 20.3-r2.x
juniper / junos 20.3-r1 20.3-r1.x
juniper / junos 20.4-r1 20.4-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-r2 20.3-r2.x
juniper / junos_os_evolved 20.3-r1 20.3-r1.x
juniper / junos_os_evolved 20.4-r1 20.4-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.