Vulnerability Database

346,508

Total vulnerabilities in the database

CVE-2021-31364 — juniper / junos

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

An Improper Check for Unusual or Exceptional Conditions vulnerability combined with a Race Condition in the flow daemon (flowd) of Juniper Networks Junos OS on SRX300 Series, SRX500 Series, SRX1500, and SRX5000 Series with SPC2 allows an unauthenticated network based attacker sending specific traffic to cause a crash of the flowd/srxpfe process, responsible for traffic forwarding in SRX, which will cause a Denial of Service (DoS). Continued receipt and processing of this specific traffic will create a sustained Denial of Service (DoS) condition. This issue can only occur when specific packets are trying to create the same session and logging for session-close is configured as a policy action. Affected platforms are: SRX300 Series, SRX500 Series, SRX1500, and SRX5000 Series with SPC2. Not affected platforms are: SRX4000 Series, SRX5000 Series with SPC3, and vSRX Series. This issue affects Juniper Networks Junos OS SRX300 Series, SRX500 Series, SRX1500, and SRX5000 Series with SPC2: All versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3; 20.3 versions prior to 20.3R2-S1, 20.3R3; 20.4 versions prior to 20.4R2.

  • Published: Oct 19, 2021
  • Updated: Nov 16, 2025
  • CVE: CVE-2021-31364
  • 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: Low
  • Score: 4.3
  • AV:N/AC:M/Au:N/C:N/I:N/A:P
Software From Fixed in
juniper / junos 17.4-r1 17.4-r1.x
juniper / junos 17.4-r2 17.4-r2.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-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 17.4.x
juniper / junos 17.4-r1-s5 17.4-r1-s5.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-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-r2-s8 17.4-r2-s8.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-s11 17.4-r2-s11.x
juniper / junos 17.4-r2-s12 17.4-r2-s12.x
juniper / junos 17.4-r3-s4 17.4-r3-s4.x
juniper / junos 17.4-r2-s13 17.4-r2-s13.x
juniper / junos 18.3-r 18.3-r.x
juniper / junos 18.3-r2-s4 18.3-r2-s4.x
juniper / junos 18.3-r3-s3 18.3-r3-s3.x
juniper / junos 18.3-r3-s2 18.3-r3-s2.x
juniper / junos 18.3-r2-s3 18.3-r2-s3.x
juniper / junos 18.3-r3-s4 18.3-r3-s4.x
juniper / junos 18.3-r3-s1 18.3-r3-s1.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-r1-s3 18.3-r1-s3.x
juniper / junos 18.3-r1-s4 18.3-r1-s4.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-s1 18.3-r1-s1.x
juniper / junos 18.4-r1 18.4-r1.x
juniper / junos 18.4 18.4.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-r2-s2 18.4-r2-s2.x
juniper / junos 18.4-r1-s5 18.4-r1-s5.x
juniper / junos 18.4-r2-s1 18.4-r2-s1.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-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-s6 18.4-r3-s6.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-r2-s6 18.4-r2-s6.x
juniper / junos 18.4-r1-s6 18.4-r1-s6.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-s8 18.4-r3-s8.x
juniper / junos 18.4-r3-s10 18.4-r3-s10.x
juniper / junos 18.4-r2-s8 18.4-r2-s8.x
juniper / junos 18.4-r2-s7 18.4-r2-s7.x
juniper / junos 18.4-r3-s7 18.4-r3-s7.x
juniper / junos 19.1-r2-s2 19.1-r2-s2.x
juniper / junos 19.1-r1-s6 19.1-r1-s6.x
juniper / junos 19.1-r3-s5 19.1-r3-s5.x
juniper / junos 19.1-r2-s3 19.1-r2-s3.x
juniper / junos 19.1-r3-s2 19.1-r3-s2.x
juniper / junos 19.1-r1-s4 19.1-r1-s4.x
juniper / junos 19.1-r1-s5 19.1-r1-s5.x
juniper / junos 19.1-r3-s3 19.1-r3-s3.x
juniper / junos 19.1-r3-s4 19.1-r3-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 19.1-r2 19.1-r2.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 19.2-r1 19.2-r1.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-s4 19.2-r1-s4.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-r1-s6 19.2-r1-s6.x
juniper / junos 19.2-r3-s1 19.2-r3-s1.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 19.3-r2-s3 19.3-r2-s3.x
juniper / junos 19.3-r2-s4 19.3-r2-s4.x
juniper / junos 19.3-r2-s2 19.3-r2-s2.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 19.3.x
juniper / junos 19.3-r1 19.3-r1.x
juniper / junos 19.3-r2 19.3-r2.x
juniper / junos 19.4-r1 19.4-r1.x
juniper / junos 19.4-r1-s1 19.4-r1-s1.x
juniper / junos 19.4-r1-s2 19.4-r1-s2.x
juniper / junos 19.4-r3 19.4-r3.x
juniper / junos 19.4-r3-s2 19.4-r3-s2.x
juniper / junos 19.4-r1-s3 19.4-r1-s3.x
juniper / junos 19.4-r3-s1 19.4-r3-s1.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 20.1-r1-s2 20.1-r1-s2.x
juniper / junos 20.1-r1-s3 20.1-r1-s3.x
juniper / junos 20.1-r1-s1 20.1-r1-s1.x
juniper / junos 20.1-r1 20.1-r1.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 20.2-r2-s3 20.2-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 20.2-r1-s3 20.2-r1-s3.x
juniper / junos 20.2-r2-s2 20.2-r2-s2.x
juniper / junos 20.3-r2 20.3-r2.x
juniper / junos 20.3-r1 20.3-r1.x
juniper / junos 20.3-r1-s1 20.3-r1-s1.x
juniper / junos 20.4-r1-s1 20.4-r1-s1.x
juniper / junos 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.