Vulnerability Database

346,508

Total vulnerabilities in the database

CVE-2026-4247 — freebsd / freebsd

Missing Release of Memory after Effective Lifetime

When a challenge ACK is to be sent tcp_respond() constructs and sends the challenge ACK and consumes the mbuf that is passed in. When no challenge ACK should be sent the function returns and leaks the mbuf.

If an attacker is either on path with an established TCP connection, or can themselves establish a TCP connection, to an affected FreeBSD machine, they can easily craft and send packets which meet the challenge ACK criteria and cause the FreeBSD host to leak an mbuf for each crafted packet in excess of the configured rate limit settings i.e. with default settings, crafted packets in excess of the first 5 sent within a 1s period will leak an mbuf.

Technically, off-path attackers can also exploit this problem by guessing the IP addresses, TCP port numbers and in some cases the sequence numbers of established connections and spoofing packets towards a FreeBSD machine, but this is harder to do effectively.

  • Published: Mar 26, 2026
  • Updated: Mar 31, 2026
  • CVE: CVE-2026-4247
  • 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
freebsd / freebsd 14.3 14.3.x
freebsd / freebsd 14.3-p1 14.3-p1.x
freebsd / freebsd 14.3-p2 14.3-p2.x
freebsd / freebsd 14.3-p3 14.3-p3.x
freebsd / freebsd 14.3-p4 14.3-p4.x
freebsd / freebsd 14.3-p5 14.3-p5.x
freebsd / freebsd 14.3-p6 14.3-p6.x
freebsd / freebsd 14.3-p7 14.3-p7.x
freebsd / freebsd 14.3-p8 14.3-p8.x
freebsd / freebsd 14.3-p9 14.3-p9.x
freebsd / freebsd 14.4 14.4.x
freebsd / freebsd 14.4-rc1 14.4-rc1.x
freebsd / freebsd 15.0 15.0.x
freebsd / freebsd 15.0-p1 15.0-p1.x
freebsd / freebsd 15.0-p2 15.0-p2.x
freebsd / freebsd 15.0-p3 15.0-p3.x
freebsd / freebsd 15.0-p4 15.0-p4.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.