CVE-2026-4247Network attack vector

Remote service interruption via challenge ACK mbuf leak

Published Mar 26, 2026 · Updated Mar 26, 2026

Memory leak in FreeBSD 14.x and 15.0 TCP handling allows remote attackers to exhaust mbufs with crafted challenge-ACK traffic. In tcp_subr.c, tcp_respond() returns without freeing its input mbuf when challenge ACK rate limiting suppresses a response, leaking one buffer for every excess qualifying segment. An on-path attacker or a remote peer with an established TCP connection can repeatedly consume kernel network buffers and interrupt service; off-path spoofing requires connection-tuple and sometimes sequence-number guesses.

CVSS severity7.5
High
EPSS probability1.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in FreeBSD 14.x and 15.0 TCP handling allows remote attackers to exhaust mbufs with crafted challenge-ACK traffic. In tcp_subr.c, tcp_respond() returns without freeing its input mbuf when challenge ACK rate limiting suppresses a response, leaking one buffer for every excess qualifying segment. An on-path attacker or a remote peer with an established TCP connection can repeatedly consume kernel network buffers and interrupt service; off-path spoofing requires connection-tuple and sometimes sequence-number guesses.

The record

CVE
CVE-2026-4247
Published
Mar 26, 2026
Updated
Mar 26, 2026
Vendor
The FreeBSD Project
Product
FreeBSD
Classifications
CWE-401, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 26, 2026Record 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=14.3-RELEASE <p10
  2. Affected versionversion=14.4-RELEASE <p1
  3. Affected versionversion=15.0-RELEASE <p5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The FreeBSD Project · FreeBSDversion=14.3-RELEASE <p10; version=14.4-RELEASE <p1; version=15.0-RELEASE <p5

Published CVSS scores

7.5CISA-ADPCVSS: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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