CVE-2020-7451Network attack vector

Kernel memory disclosure via uninitialized Traffic Class

Published Apr 28, 2020 · Updated Aug 4, 2024

Kernel information disclosure in FreeBSD 11.3 and 12.1 allows remote attackers to read one byte of kernel memory via IPv6 TCP replies. The IPv6 TCP response path leaves the Traffic Class field uninitialized when transmitting or retransmitting SYN-ACK or challenge ACK segments, copying a residual kernel byte onto the network. An unauthenticated attacker must elicit and observe an affected IPv6 reply; disclosure is limited to one byte per segment.

CVSS severity5.3
Medium
EPSS probability1.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Kernel information disclosure in FreeBSD 11.3 and 12.1 allows remote attackers to read one byte of kernel memory via IPv6 TCP replies. The IPv6 TCP response path leaves the Traffic Class field uninitialized when transmitting or retransmitting SYN-ACK or challenge ACK segments, copying a residual kernel byte onto the network. An unauthenticated attacker must elicit and observe an affected IPv6 reply; disclosure is limited to one byte per segment.

The record

CVE
CVE-2020-7451
Published
Apr 28, 2020
Updated
Aug 4, 2024
Vendor
The FreeBSD Project
Product
FreeBSD
Classifications
CWE-908
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 28, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=12.1-STABLE before r358739, 12.1-RELEASE before 12.1-RELEASE-p3, 11.3-STABLE before r358740, 11.3-RELEASE before 11.3-RELEASE-p7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The FreeBSD Project · FreeBSDversion=12.1-STABLE before r358739, 12.1-RELEASE before 12.1-RELEASE-p3, 11.3-STABLE before r358740, 11.3-RELEASE before 11.3-RELEASE-p7

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N

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

CWE-908Use of Uninitialized Resource

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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