Vulnerability Database

328,409

Total vulnerabilities in the database

CVE-2026-21918

A Double Free vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX and MX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). On all SRX and MX Series platforms, when during TCP session establishment a specific sequence of packets is encountered a double free happens. This causes flowd to crash and the respective FPC to restart.

This issue affects Junos OS on SRX and MX Series:

  • all versions before 22.4R3-S7,
  • 23.2 versions before 23.2R2-S3,
  • 23.4 versions before 23.4R2-S4,
  • 24.2 versions before 24.2R2.
  • Published: Jan 15, 2026
  • Updated: Jan 16, 2026
  • CVE: CVE-2026-21918
  • Severity: High
  • Exploit:

CVSS v3:

  • Severity: High
  • Score: 7.5
  • AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWEs:

Software From Fixed in
juniper / junos - 22.4
juniper / junos 22.4 22.4.x
juniper / junos 22.4-r1 22.4-r1.x
juniper / junos 22.4-r1-s1 22.4-r1-s1.x
juniper / junos 22.4-r1-s2 22.4-r1-s2.x
juniper / junos 22.4-r2 22.4-r2.x
juniper / junos 22.4-r2-s1 22.4-r2-s1.x
juniper / junos 22.4-r2-s2 22.4-r2-s2.x
juniper / junos 22.4-r3 22.4-r3.x
juniper / junos 22.4-r3-s1 22.4-r3-s1.x
juniper / junos 22.4-r3-s2 22.4-r3-s2.x
juniper / junos 22.4-r3-s3 22.4-r3-s3.x
juniper / junos 22.4-r3-s4 22.4-r3-s4.x
juniper / junos 22.4-r3-s5 22.4-r3-s5.x
juniper / junos 22.4-r3-s6 22.4-r3-s6.x
juniper / junos 23.2 23.2.x
juniper / junos 23.2-r1 23.2-r1.x
juniper / junos 23.2-r1-s1 23.2-r1-s1.x
juniper / junos 23.2-r1-s2 23.2-r1-s2.x
juniper / junos 23.2-r2 23.2-r2.x
juniper / junos 23.2-r2-s1 23.2-r2-s1.x
juniper / junos 23.2-r2-s2 23.2-r2-s2.x
juniper / junos 23.4 23.4.x
juniper / junos 23.4-r1 23.4-r1.x
juniper / junos 23.4-r1-s1 23.4-r1-s1.x
juniper / junos 23.4-r1-s2 23.4-r1-s2.x
juniper / junos 23.4-r2 23.4-r2.x
juniper / junos 23.4-r2-s1 23.4-r2-s1.x
juniper / junos 23.4-r2-s2 23.4-r2-s2.x
juniper / junos 23.4-r2-s3 23.4-r2-s3.x
juniper / junos 24.2 24.2.x
juniper / junos 24.2-r1 24.2-r1.x
juniper / junos 24.2-r1-s1 24.2-r1-s1.x
juniper / junos 24.2-r1-s2 24.2-r1-s2.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.