FreeBSDOperating system
CVE-2021-29626
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 n245117, 12.2-STABLE before r369551, 11.4-STABLE before r369559, 13.0-RC5 before p1, 12.2-RELEASE before p6, and 11.4-RELEASE before p9, copy-on-write logic failed to invalidate shared memory page mappings between multiple processes allowing an unprivileged process to maintain a mapping after it is freed, allowing the process to read private data belonging to other processes or the kernel.
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 copy-on-write (COW) logic flaw in the FreeBSD kernel fails to properly invalidate shared memory page mappings when pages are freed. This allows an unprivileged process to retain read access to memory pages after they have been released, potentially exposing private data from other processes or the kernel that later uses those memory pages.
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
< 11.4>= 12.0, < 12.2= 11.4= 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
- None
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
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 installed FreeBSD versionRun `uname -a` or `freebsd-version -u` to determine the exact FreeBSD version running on the systemAffected if The version falls within < 11.4, >= 12.0 and < 12.2, or equals 11.4, 12.2, or 13.0
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Verify shared memory subsystem usageRun `ipcs -m` to list active shared memory segments, or check for processes using shmget/shmat syscalls via `procstat -a | grep -i shm`Affected if The system actively uses POSIX or System V shared memory and the FreeBSD version is vulnerable
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Check for large page or COW-enabled allocationsExamine if any processes allocate memory with MAP_COW or large page flags using `vmstat -s` and reviewing dmesg for related kernel messagesAffected if COW-mapped memory exists on the system and the kernel version is unpatched
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Review kernel source for COW handlingIf kernel source is available, verify whether the fix from r369551 (12.2) or r369559 (11.4) is present by checking the relevant shm子系统 code in the kernelAffected if The specific COW invalidation fix is absent from the running kernel
A system is affected if it runs a FreeBSD version in the affected list and utilizes shared memory or COW page mappings, allowing potential cross-process memory exposure.
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 data11.412.2
Upgrade FreeBSD systems to the patched versions: 13.0-STABLE after n245117, 12.2-STABLE after r369551, 11.4-STABLE after r369559, or respective release patches p1, p6, p9 or later.
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-2021-29626 — 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-2021-29626 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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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- 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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