CVE-2023-6534Network attack vector

Host denial of service via TCP stream injection

Published Dec 13, 2023 · Updated Feb 13, 2025

TCP spoofing in affected FreeBSD 12.4, 13.2, and 14.0 releases allows remote attackers to interrupt hosts behind pf firewalls. During stateful tracking, pf accepts inbound TCP sequence numbers without actually validating them against the stored connection state. Exploitation requires impersonating the remote host and guessing the connection's port numbers; injected TCP RST packets can terminate established connections.

CVSS severity7.5
High
EPSS probability0.74%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

TCP spoofing in affected FreeBSD 12.4, 13.2, and 14.0 releases allows remote attackers to interrupt hosts behind pf firewalls. During stateful tracking, pf accepts inbound TCP sequence numbers without actually validating them against the stored connection state. Exploitation requires impersonating the remote host and guessing the connection's port numbers; injected TCP RST packets can terminate established connections.

The record

CVE
CVE-2023-6534
Published
Dec 13, 2023
Updated
Feb 13, 2025
Vendor
The FreeBSD Project
Product
FreeBSD
Classifications
T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 13, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=12.4-RELEASE <p9
  2. Affected versionversion=13.2-RELEASE <p7
  3. Affected versionversion=14.0-RELEASE <p2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The FreeBSD Project · FreeBSDversion=12.4-RELEASE <p9; version=13.2-RELEASE <p7; version=14.0-RELEASE <p2

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1498Network Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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