How severe is CVE-2023-6534?

CVE-2023-6534 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2023-6534 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (50th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-6534?

CVE-2023-6534 primarily affects Freebsd. In total, 23 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-6534?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2023-6534 published?

CVE-2023-6534 was published on 2023-12-13 and last updated on 2026-06-17.

CVE-2023-6534

CVE-2023-6534 is a high-severity vulnerability in Freebsd with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 1% (50th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Freebsd
Published: 2023-12-13
Last modified: 2026-06-17

Description

In versions of FreeBSD 14.0-RELEASE before 14-RELEASE-p2, FreeBSD 13.2-RELEASE before 13.2-RELEASE-p7 and FreeBSD 12.4-RELEASE before 12.4-RELEASE-p9, the pf(4) packet filter incorrectly validates TCP sequence numbers. This could allow a malicious actor to execute a denial-of-service attack against hosts behind the firewall.

Frequently asked questions

What is CVE-2023-6534?: In versions of FreeBSD 14.0-RELEASE before 14-RELEASE-p2, FreeBSD 13.2-RELEASE before 13.2-RELEASE-p7 and FreeBSD 12.4-RELEASE before 12.4-RELEASE-p9, the pf(4) packet filter incorrectly validates TCP sequence numbers. This could allow a malicious actor to execute a denial-of-service attack against hosts behind the firewall.
How severe is CVE-2023-6534?: CVE-2023-6534 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2023-6534 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (50th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-6534?: CVE-2023-6534 primarily affects Freebsd. In total, 23 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2023-6534?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2023-6534 published?: CVE-2023-6534 was published on 2023-12-13 and last updated on 2026-06-17.

References

Affected products (23)

cpe:2.3:o:freebsd:freebsd:12.4:-:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p1:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p2:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p3:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p4:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p5:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p6:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p7:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:p8:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:rc2-p1:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:12.4:rc2-p2:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:13.2:-:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:13.2:p1:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:13.2:p2:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:13.2:p3:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:13.2:p4:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:13.2:p5:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:13.2:p6:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:14.0:-:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:14.0:beta5:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:14.0:p1:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:14.0:rc3:*:*:*:*:*:*
cpe:2.3:o:freebsd:freebsd:14.0:rc4-p1:*:*:*:*:*:*

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