CVE-2021-30738
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 · uneditedA malicious application may be able to overwrite arbitrary files. This issue is fixed in macOS Big Sur 11.4, Security Update 2021-004 Mojave. An issue with path validation logic for hardlinks was addressed with improved path sanitization.
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 · moderate confidenceA malicious application can overwrite arbitrary files due to insufficient path validation in macOS hardlink handling logic. The vulnerability stems from improper path sanitization that fails to properly validate hardlink paths, allowing local privilege escalation through arbitrary file writes.
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>= 10.14.0, <= 10.14.5= 10.14.6>= 11.0.1, < 11.4CVSS 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
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/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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Determine installed macOS versionRun `sw_vers -productVersion` in Terminal or select Apple menu > About This MacAffected if version falls within 10.14.0-10.14.5, equals exactly 10.14.6, or falls within 11.0.1-11.3.x
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Check if security update is installedRun `system_profiler SPSoftwareDataType` and look for 'Security Update 2021-004' (Mojave) or 'macOS 11.4' (Big Sur) in the installed updatesAffected if the applicable security update or macOS 11.4 is not listed as installed
The environment is affected if the system runs macOS Mojave 10.14.0-10.14.6 or macOS Big Sur 11.0.1-11.3.x without the respective security updates applied.
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.
dbcve · scoped11.4
Apply the vendor-supplied security updates: macOS Big Sur 11.4 or Security Update 2021-004 for Mojave. These updates contain improved path sanitization for hardlink validation logic.
macOS 11.4 or later for Big Sur users; Security Update 2021-004 for Mojave users
- For macOS 11.x (Big Sur) users: Upgrade to macOS 11.4 or later by going to System Preferences > Software Update and installing the latest update.
- For macOS 10.14.x (Mojave) users: Apply Security Update 2021-004 Mojave by going to System Preferences > Software Update and installing the security update.
- Alternatively, manually download the update from Apple Support and install it.
- After updating, verify the system is running the fixed version: macOS 11.4+ or the Security Update 2021-004 installed.
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,304.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-30738 — 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-2021-30738 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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