CVE-2026-63952: memfd: deny writeable mappings when implying SEAL_WRITE

Severity: high (CVSS 8.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-19 · updated 2026-10-28
Weakness: CWE-362

Description

In 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.

Affected products

Linux kernel: from 6.3 before 6.6.143; from 6.7 before 6.12.93; from 6.13 before 6.18.35; from 6.19 before 7.0.12; 7.1-rc1, 7.1-rc2, 7.1-rc3, 7.1-rc4, 7.1-rc5 — fixed in 6.6.143, 6.12.93, 6.18.35, 7.0.12
Linux kernel: 6.3 — fixed in 7.1

How to fix

Upgrade to a fixed version: Linux kernel 6.6.143, 6.12.93, 6.18.35, 7.0.12; Linux kernel 7.1. Check the vendor advisory for mitigations.

References

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