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CVE-2026-63952 (GCVE-0-2026-63952)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-08-05 12:37
VLAI
Title
memfd: deny writeable mappings when implying SEAL_WRITE
Summary
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.
Severity
8.4 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: c4f75bc8bd6b3d62665e1f5400c419540edb5601 , < b3f4f82d1315f1439059a83d1c22c51a5b43d99e (git)
Affected: c4f75bc8bd6b3d62665e1f5400c419540edb5601 , < 3be2a24f7f72ad7321ed6ad1715b956a4527bcf4 (git)
Affected: c4f75bc8bd6b3d62665e1f5400c419540edb5601 , < 0995d1f79aed8ccbf62056189dd53fd19726ea08 (git)
Affected: c4f75bc8bd6b3d62665e1f5400c419540edb5601 , < 555702282d4536a865dfffb1cd4f6028f196e7e8 (git)
Affected: c4f75bc8bd6b3d62665e1f5400c419540edb5601 , < 3b041514cb6eae45869b020f743c14d983363222 (git)
guessed Create a notification for this product.
Linux Linux Affected: 6.3
Unaffected: 0 , < 6.3 (semver)
Unaffected: 6.6.143 , ≤ 6.6.* (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/memfd.c"
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          "versions": [
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              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "semver"
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              "status": "unaffected",
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmemfd: deny writeable mappings when implying SEAL_WRITE\n\nWhen SEAL_EXEC is added, SEAL_WRITE is implied to make W^X.  But the\nimplied seal is set after the check that makes sure the memfd can not have\nany writable mappings.  This means one can use SEAL_EXEC to apply\nSEAL_WRITE while having writeable mappings.\n\nThis breaks the contract that SEAL_WRITE provides and can be used by an\nattacker to pass a memfd that appears to be write sealed but can still be\nmodified arbitrarily.\n\nFix this by adding the implied seals before the call for\nmapping_deny_writable() is done."
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N",
            "version": "3.1"
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              "value": "AV:L - Exploitation requires local syscalls (memfd_create, mmap, fcntl) with no network-facing code path; the vulnerable logic is reached only through the local fcntl(F_ADD_SEALS) interface on a memfd file descriptor.\nAC:L - The attack is a reliable, deterministic syscall sequence (create executable memfd, establish a writable MAP_SHARED mapping, then apply F_SEAL_EXEC) with no race or attacker-uncontrollable conditions.\nPR:L - Any unprivileged local user can invoke memfd_create, mmap, and fcntl without capabilities; these interfaces are available inside unprivileged user namespaces with no real-root requirement.\nUI:N - Exploitation does not require a human victim action; in the highest-impact scenario a sandboxed process programmatically passes the sealed-appearing memfd to a trusting peer via IPC (e.g., SCM_RIGHTS) without user interaction.\nS:C - The bug breaks the memfd seal security contract designed for mutually untrusted parties, allowing a malicious local peer to deceive a separate process that relies on F_SEAL_WRITE immutability, crossing the inter-process trust boundary (sandbox/W^X enforcement).\nC:H - Bypassing write-seal/W^X guarantees enables arbitrary modification of executable memfd contents presented as immutable, which can be leveraged for arbitrary code execution in a trusting victim process and thereby full read of that process\u0027s memory.\nI:H - The vulnerability allows arbitrary modification of memory that is advertised as write-sealed (F_SEAL_WRITE), defeating the kernel\u0027s immutability guarantee and enabling W^X bypass and code injection into trusted execution contexts.\nA:N - The flaw is a logic error in seal enforcement that does not cause kernel crashes, panics, hangs, or denial of service; exploitation maintains availability while subverting integrity guarantees."
            }
          ]
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        "dateUpdated": "2026-08-05T12:37:37.398Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/3b041514cb6eae45869b020f743c14d983363222"
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    "cveId": "CVE-2026-63952",
    "datePublished": "2026-07-19T14:55:44.809Z",
    "dateReserved": "2026-07-19T07:54:57.023Z",
    "dateUpdated": "2026-08-05T12:37:37.398Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-16T05:36:32+00:00",
      "cve": "CVE-2026-63952",
      "id": "CVE-2026-63952",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:fixed": "917",
      "product_status:known_affected": "22",
      "product_status:known_not_affected": "91",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: memfd: deny writeable mappings when implying SEAL_WRITE",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63952.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-10T16:48:54Z",
      "cve": "CVE-2026-63952",
      "id": "CVE-2026-63952",
      "initial_release_date": "2026-07-21T13:02:52Z",
      "product_status:first_fixed": "2",
      "product_status:known_affected": "423",
      "product_status:known_not_affected": "251",
      "product_status:recommended": "364",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-63952",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63952.json",
      "version": "19"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.