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vuln-cve/data/2025/21xxx/CVE-2025-21836.json
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{
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"cveMetadata": {
"cveId": "CVE-2025-21836",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2024-12-29T08:45:45.777Z",
"datePublished": "2025-03-07T09:09:56.127Z",
"dateUpdated": "2026-10-15T21:51:53.980Z"
},
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"cna": {
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"dateUpdated": "2026-08-05T11:54:49.695Z"
},
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/kbuf: reallocate buf lists on upgrade\n\nIORING_REGISTER_PBUF_RING can reuse an old struct io_buffer_list if it\nwas created for legacy selected buffer and has been emptied. It violates\nthe requirement that most of the field should stay stable after publish.\nAlways reallocate it instead."
}
],
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"baseScore": 7.8,
"baseSeverity": "HIGH"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The vulnerable code is reached only through the io_uring_setup/io_uring_register syscalls; there is no network or adjacent path, so exploitation requires local access to issue syscalls.\nAC:L - The attacker performs every step themselves (create a legacy buffer group, empty it, upgrade the same bgid via PBUF_RING, then mmap), controlling both sides of any race; the trigger is fully deterministic and reliable.\nPR:L - io_uring is available to unprivileged users by default (kernel.io_uring_disabled=0) and provided-buffer registration needs no capability, so only a basic local user account is required.\nUI:N - The entire sequence is driven by the attacking process; no action by any other user or victim is needed.\nS:U - The corruption is confined to the kernel's own security authority (standard local privilege escalation) and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - The type confusion / use-after-free of the io_buffer_list and the retained user mapping to freed kernel pages give the attacker read access to reallocated kernel memory, enabling arbitrary kernel information disclosure.\nI:H - The same UAF and shared-page primitive give write access to freed/reallocated kernel memory, exploitable for arbitrary kernel write and privilege escalation as demonstrated for this io_uring buffer-ring bug class.\nA:H - At minimum the type confusion and use-after-free corrupt kernel structures, causing an oops/panic and denial of service."
}
]
}
],
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"product": "Linux",
"vendor": "Linux",
"defaultStatus": "unaffected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"io_uring/kbuf.c"
],
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"version": "2fcabce2d7d34f69a888146dab15b36a917f09d4",
"lessThan": "146a185f6c05ee263db715f860620606303c4633",
"status": "affected",
"versionType": "git"
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"status": "affected",
"versionType": "git"
},
{
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"lessThan": "8802766324e1f5d414a81ac43365c20142e85603",
"status": "affected",
"versionType": "git"
}
]
},
{
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"vendor": "Linux",
"defaultStatus": "affected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"io_uring/kbuf.c"
],
"versions": [
{
"version": "5.19",
"status": "affected"
},
{
"version": "0",
"lessThan": "5.19",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.6.79",
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.12.16",
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.13.4",
"lessThanOrEqual": "6.13.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.14",
"lessThanOrEqual": "*",
"status": "unaffected",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"operator": "OR",
"negate": false,
"cpeMatch": [
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"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.19",
"versionEndExcluding": "6.6.79"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.19",
"versionEndExcluding": "6.12.16"
},
{
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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],
"references": [
{
"url": "https://git.kernel.org/stable/c/146a185f6c05ee263db715f860620606303c4633"
},
{
"url": "https://git.kernel.org/stable/c/7d0dc28dae836caf7645fef62a10befc624dd17b"
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{
"url": "https://git.kernel.org/stable/c/2a5febbef40ce968e295a7aeaa5d5cbd9e3e5ad4"
},
{
"url": "https://git.kernel.org/stable/c/8802766324e1f5d414a81ac43365c20142e85603"
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{
"url": "https://u1f383.github.io/slides/talks/2025_Hexacon-Deja_Vu_in_Linux_io_uring_Breaking_Memory_Sharing_Again_After_Generations_of_Fixes.pdf"
}
],
"title": "io_uring/kbuf: reallocate buf lists on upgrade",
"x_generator": {
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}
},
"adp": [
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"metrics": [
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"other": {
"type": "ssvc",
"content": {
"id": "CVE-2025-21836",
"role": "CISA Coordinator",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"version": "2.0.3",
"timestamp": "2026-10-15T21:43:15.462435Z"
}
}
}
],
"title": "CISA ADP Vulnrichment",
"providerMetadata": {
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"dateUpdated": "2026-10-15T21:51:53.980Z"
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}