VulnerabilityPublished 19 Jul 2026

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

Source GCVE Database

Authoritative record:CVE-2026-63952· High 8.4

Not known to be exploited · CVSS 8.4 High · fixed in b3f4f82d1315f1439059a83d1c22c51a5b43d99e : patch Linux kernel soon.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

8.4High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 2% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in b3f4f82d1315f1439059a83d1c22c51a5b43d99e, 555702282d4536a865dfffb1cd4f6028f196e7e8, 0995d1f79aed8ccbf62056189dd53fd19726ea08 +2

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-6pc4-h32v-99rg

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ c4f75bc8bd6b3d62665e1f5400c419540edb5601, < b3f4f82d1315f1439059a83d1c22c51a5b43d99e	Fixed in b3f4f82d1315f1439059a83d1c22c51a5b43d99e
LinuxLinux	Affected ≥ c4f75bc8bd6b3d62665e1f5400c419540edb5601, < 555702282d4536a865dfffb1cd4f6028f196e7e8	Fixed in 555702282d4536a865dfffb1cd4f6028f196e7e8
LinuxLinux	Affected ≥ c4f75bc8bd6b3d62665e1f5400c419540edb5601, < 0995d1f79aed8ccbf62056189dd53fd19726ea08	Fixed in 0995d1f79aed8ccbf62056189dd53fd19726ea08
LinuxLinux	Affected ≥ c4f75bc8bd6b3d62665e1f5400c419540edb5601, < 3be2a24f7f72ad7321ed6ad1715b956a4527bcf4	Fixed in 3be2a24f7f72ad7321ed6ad1715b956a4527bcf4
LinuxLinux	Affected ≥ c4f75bc8bd6b3d62665e1f5400c419540edb5601, < 3b041514cb6eae45869b020f743c14d983363222	Fixed in 3b041514cb6eae45869b020f743c14d983363222
LinuxLinux	Affected =6.3	Fixed in–

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.

Impact

An attacker could exploit this vulnerability to modify memfd contents that are supposed to be write-protected by SEAL_WRITE, potentially undermining security mechanisms relying on memfd immutability guarantees. This could affect processes or components that depend on memfd seals to enforce memory protection policies.

Summary

The Linux kernel memfd feature uses seals to restrict modifications. When SEAL_EXEC is added, SEAL_WRITE is implicitly applied to enforce a write-protection policy (W^X). However, the original implementation applied the implied SEAL_WRITE after the check that denies writable mappings, allowing writable mappings to exist despite the seal. This flaw permits an attacker to present a memfd as write-sealed while retaining writable access, violating the seal's contract. The fix involves applying the implied seals before the writable mapping denial check, restoring the intended protection.

References

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