CVE-2026-63952

Local memfd tampering via delayed implied write seal

Published Jul 19, 2026 · Updated Jul 19, 2026

Improper memfd sealing in the Linux Kernel allows local users to alter executable memfd contents through a retained writable mapping. The memfd_add_seals function adds F_SEAL_WRITE implied by F_SEAL_EXEC only after checking for writable mappings, so an existing mapping remains writable after the seal is reported. Local low-privileged access is required, and impact crosses a trust boundary only when another component accepts the apparently write-sealed memfd.

CVSS severity8.4
High
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper memfd sealing in the Linux Kernel allows local users to alter executable memfd contents through a retained writable mapping. The memfd_add_seals function adds F_SEAL_WRITE implied by F_SEAL_EXEC only after checking for writable mappings, so an existing mapping remains writable after the seal is reported. Local low-privileged access is required, and impact crosses a trust boundary only when another component accepts the apparently write-sealed memfd.

The record

CVE
CVE-2026-63952
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
Unavailable
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 2026Record 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=6.3
  2. Affected versionversion=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <0995d1f79aed8ccbf62056189dd53fd19726ea08
  3. Affected versionversion=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <3b041514cb6eae45869b020f743c14d983363222
  4. Affected versionversion=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <3be2a24f7f72ad7321ed6ad1715b956a4527bcf4
  5. Affected versionversion=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <555702282d4536a865dfffb1cd4f6028f196e7e8
  6. Affected versionversion=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <b3f4f82d1315f1439059a83d1c22c51a5b43d99e

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=6.3; version=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <0995d1f79aed8ccbf62056189dd53fd19726ea08; version=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <3b041514cb6eae45869b020f743c14d983363222; version=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <3be2a24f7f72ad7321ed6ad1715b956a4527bcf4; version=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <555702282d4536a865dfffb1cd4f6028f196e7e8; version=c4f75bc8bd6b3d62665e1f5400c419540edb5601 <b3f4f82d1315f1439059a83d1c22c51a5b43d99e

Published CVSS scores

8.4kernel.orgCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

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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