FreeBSDOperating system
CVE-2021-29627
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn FreeBSD 13.0-STABLE before n245050, 12.2-STABLE before r369525, 13.0-RC4 before p0, and 12.2-RELEASE before p6, listening socket accept filters implementing the accf_create callback incorrectly freed a process supplied argument string. Additional operations on the socket can lead to a double free or use after free.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA memory management vulnerability in FreeBSD's socket accept filter mechanism (accf_create callback) causes incorrect freeing of a process-supplied argument string, leading to double free or use-after-free conditions. This kernel-level flaw can be triggered by local attackers using accept filters on listening sockets.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
FreeBSDOperating system
>= 12.0, < 12.2= 12.2= 13.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check FreeBSD versionRun `uname -r` or `freebsd-version` to obtain the installed FreeBSD versionAffected if The version is 12.0, 12.1, 12.2, or 13.0 (excluding patches specified in the fixed versions)
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Verify accept filter kernel modules are loadedRun `kldstat | grep -E 'accf|accept'` to list loaded accept filter modulesAffected if Any accf-related kernel modules are loaded (such as accf_data, accf_http, accf_unloadable)
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Identify listening sockets with accept filters appliedRun `sockstat -L` or examine socket configuration in /etc/rc.conf and application configurations for 'accf' or 'accept_filter' directivesAffected if Any listening sockets have accept filters configured or applied, particularly on services that accept connections
A system is potentially affected if it runs a vulnerable FreeBSD version (12.0-12.2 or 13.0) AND has accept filter kernel modules loaded with accept filters configured on listening sockets.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data12.2
Upgrade FreeBSD to version 13.0-STABLE n245050 or later, 12.2-STABLE r369525 or later, 13.0-RC4 p0 or later, or 12.2-RELEASE p6 or later. If upgrading is not immediately possible, disable or avoid using accept filters on listening sockets.
Fix this in FreeBSD
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-29627 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-29627 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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