CVE-2026-63952
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 the Linux kernel, the following vulnerability has been resolved: memfd: deny writeable mappings when implying SEAL_WRITE When SEAL_EXEC is added, SEAL_WRITE is implied to make W^X. But the implied seal is set after the check that makes sure the memfd can not have any writable mappings. This means one can use SEAL_EXEC to apply SEAL_WRITE while having writeable mappings. This breaks the contract that SEAL_WRITE provides and can be used by an attacker to pass a memfd that appears to be write sealed but can still be modified arbitrarily. Fix this by adding the implied seals before the call for mapping_deny_writable() is done.
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 confidenceIn Linux kernel's memfd subsystem, when SEAL_EXEC is added, SEAL_WRITE is implied to enforce W^X (write XOR execute) protection. However, the implied SEAL_WRITE is set AFTER the check that denies writable mappings, allowing an attacker to use SEAL_EXEC to apply SEAL_WRITE while still maintaining writeable mappings. This breaks the security contract of SEAL_WRITE, permitting arbitrary modification of a memfd that appears write-sealed.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS 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
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/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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Check the running kernel versionRun `uname -r` or `cat /proc/version` to obtain the kernel version stringAffected if The kernel version is older than the version containing the fix for the memfd sealing logic flaw (the fix reorders implied seal application before the mapping_deny_writable() check)
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Identify memfd sealing usageSearch application code or system logs for calls to memfd_create() with F_SEAL_SEAL or F_SEAL_EXEC flags set, or inspect running processes using memfd regions via `/proc/<pid>/maps` looking for entries backed by memfd:Affected if Applications are using memfd_create() with sealing flags (particularly F_SEAL_EXEC which should imply SEAL_WRITE)
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Verify the kernel commit statusCheck if the kernel source contains the fix by looking for the ordering change in the memfd sealing code: the implied seals (such as SEAL_EXEC implying SEAL_WRITE) must be applied BEFORE the mapping_deny_writable() check in the kernel source file (typically mm/memfd.c or equivalent)Affected if The kernel source still applies implied seals AFTER the mapping_deny_writable() check, leaving the race condition present
The environment is affected if running a kernel version prior to the fix AND any application uses memfd sealing with F_SEAL_EXEC or other seals that should imply SEAL_WRITE.
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 dataApply the upstream kernel patch which moves the implied seal setting before the mapping_deny_writable() call. Update to a kernel version containing this fix.
- Consultation3.0 h
- Implementation2.0 h
- Testing6.0 h
- Review / QA3.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-63952 — 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-2026-63952 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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- Version or environment caveats, and links to real fixes
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