CVE-2021-29627Public exploit

Local privilege escalation via dangling accept-filter argument

Published Apr 7, 2021 · Updated Aug 3, 2024

Use-after-free in FreeBSD 12.2-RELEASE before p6 allows local users to gain privileges or read kernel memory through a listening socket. The accept-filter socket-option handler prematurely frees a process-supplied argument retained for an accf_create callback, leaving a dangling pointer that later socket operations can free again or dereference. Exposure requires a loaded third-party accept filter with that callback; no filter is loaded by default, and the base-system filters are unaffected.

CVSS severity7.8
High
EPSS probability0.75%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in FreeBSD 12.2-RELEASE before p6 allows local users to gain privileges or read kernel memory through a listening socket. The accept-filter socket-option handler prematurely frees a process-supplied argument retained for an accf_create callback, leaving a dangling pointer that later socket operations can free again or dereference. Exposure requires a loaded third-party accept filter with that callback; no filter is loaded by default, and the base-system filters are unaffected.

The record

CVE
CVE-2021-29627
Published
Apr 7, 2021
Updated
Aug 3, 2024
Vendor
The FreeBSD Project
Product
FreeBSD
Classifications
CWE-415, CWE-416, T1068
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Apr 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=FreeBSD 12.2-RELEASE before p6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

The FreeBSD Project · FreeBSDversion=FreeBSD 12.2-RELEASE before p6

Published CVSS scores

7.2NIST NVDAV:L/AC:L/Au:N/C:C/I:C/A:C
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-415Double Free
CWE-416Use After Free
T1068Exploitation for Privilege Escalation

Public exploit references

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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