CVE-2026-72422 (GCVE-0-2026-72422)
Vulnerability from cvelistv5
Published
2026-08-15 05:56
Modified
2026-08-17 05:44
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE
conn->preauth_info is shared connection state (struct
preauth_integrity_info, kmalloc-96) that is allocated and freed by the
SMB2 NEGOTIATE handler and read by the response send path.
smb2_handle_negotiate() allocates conn->preauth_info, and on a
deassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the
allocation and the free/NULL happen under ksmbd_conn_lock(conn) (the
connection srv_mutex), which is held across the whole handler body.
The response send path smb3_preauth_hash_rsp(), called from the send:
block of __handle_ksmbd_work(), reads conn->preauth_info and dereferences
conn->preauth_info->Preauth_HashValue (via
ksmbd_gen_preauth_integrity_hash()) without taking conn_lock. When a
client drives two SMB2 NEGOTIATE requests on the same connection, one
worker can free conn->preauth_info on the failing-negotiate path while a
concurrent send-path worker is reading it, producing a slab
use-after-free read (KASAN-confirmed).
The send-path read tested conn->preauth_info for NULL but raced with the
free that occurs between the NULL check and the dereference, so the NULL
guard alone does not close the window.
Serialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under
ksmbd_conn_lock(conn) and re-check conn->preauth_info inside the lock.
Because the negotiate handler holds conn_lock across its kfree + NULL
assignment, a reader that also takes conn_lock either runs fully before
the allocation or fully after the NULL store, and can never observe the
freed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash()
takes no locks itself (it only computes a SHA-512 over the buffer), so
no lock-ordering inversion is introduced, and conn_lock is a sleepable
mutex which is safe on this send path (it already performs network I/O).
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: dd4e4c811898410e6a3ae3b63207b7c542860907 Version: aa7253c2393f6dcd6a1468b0792f6da76edad917 Version: aa7253c2393f6dcd6a1468b0792f6da76edad917 Version: aa7253c2393f6dcd6a1468b0792f6da76edad917 Version: aa7253c2393f6dcd6a1468b0792f6da76edad917 Version: aa7253c2393f6dcd6a1468b0792f6da76edad917 Version: aa7253c2393f6dcd6a1468b0792f6da76edad917 Version: 8a8315a5960bd2b5ffc75f44fc089e57c3b17c44 Version: ff20f1875889dbe4a67c9298e609d7c88cf6456d Version: 5.15.61 ≤ Version: 5.18.18 ≤ Version: 5.19.2 ≤ |
||
{
"containers": {
"cna": {
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{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/smb/server/smb2pdu.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"versions": [
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{
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{
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"versionType": "git"
},
{
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"status": "affected",
"version": "5.18.18",
"versionType": "semver"
},
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"status": "affected",
"version": "5.19.2",
"versionType": "semver"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/smb/server/smb2pdu.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "6.0"
},
{
"lessThan": "6.0",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.212",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.178",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.145",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.97",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.40",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.5",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
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"versionStartIncluding": "5.15.61",
"vulnerable": true
},
{
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{
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}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free of conn-\u003epreauth_info in concurrent SMB2 NEGOTIATE\n\nconn-\u003epreauth_info is shared connection state (struct\npreauth_integrity_info, kmalloc-96) that is allocated and freed by the\nSMB2 NEGOTIATE handler and read by the response send path.\n\nsmb2_handle_negotiate() allocates conn-\u003epreauth_info, and on a\ndeassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the\nallocation and the free/NULL happen under ksmbd_conn_lock(conn) (the\nconnection srv_mutex), which is held across the whole handler body.\n\nThe response send path smb3_preauth_hash_rsp(), called from the send:\nblock of __handle_ksmbd_work(), reads conn-\u003epreauth_info and dereferences\nconn-\u003epreauth_info-\u003ePreauth_HashValue (via\nksmbd_gen_preauth_integrity_hash()) without taking conn_lock. When a\nclient drives two SMB2 NEGOTIATE requests on the same connection, one\nworker can free conn-\u003epreauth_info on the failing-negotiate path while a\nconcurrent send-path worker is reading it, producing a slab\nuse-after-free read (KASAN-confirmed).\n\nThe send-path read tested conn-\u003epreauth_info for NULL but raced with the\nfree that occurs between the NULL check and the dereference, so the NULL\nguard alone does not close the window.\n\nSerialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under\nksmbd_conn_lock(conn) and re-check conn-\u003epreauth_info inside the lock.\nBecause the negotiate handler holds conn_lock across its kfree + NULL\nassignment, a reader that also takes conn_lock either runs fully before\nthe allocation or fully after the NULL store, and can never observe the\nfreed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash()\ntakes no locks itself (it only computes a SHA-512 over the buffer), so\nno lock-ordering inversion is introduced, and conn_lock is a sleepable\nmutex which is safe on this send path (it already performs network I/O)."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:N - The bug is in ksmbd\u0027s SMB2 NEGOTIATE handler reachable by any remote client over TCP port 445 without local access; exploitation requires only crafted SMB 3.1.1 negotiate packets on an established network connection.\nAC:L - The attacker controls both sides of the race by pipelining two SMB2 NEGOTIATE requests on the same connection, with one crafted to fail deassemble_neg_contexts() and free preauth_info while the other is in the response send path; KASAN-confirmed UAF with no uncontrollable timing.\nPR:N - SMB2 NEGOTIATE is processed before any authentication or session establishment; smb2_check_user_session explicitly exempts NEGOTIATE from session validation, so an unauthenticated remote attacker can reach the vulnerable code path.\nUI:N - Exploitation requires only network packets sent by the attacker to an exposed ksmbd instance; no victim user action such as mounting a share or opening a file is needed.\nS:U - Successful exploitation compromises kernel memory on the SMB server host itself; this is standard in-kernel memory corruption without crossing a VM, container, or IOMMU security boundary to a separate authority.\nC:H - KASAN-confirmed slab use-after-free read of conn-\u003epreauth_info (kmalloc-96) via Preauth_HashValue and Preauth_HashId dereference; UAF on attacker-influenced freed heap memory enables arbitrary kernel memory disclosure through heap grooming.\nI:H - The UAF corrupts kernel heap state on a network-facing pre-auth path; freed preauth_integrity_info objects can be reallocated via heap spraying to obtain arbitrary write or control-flow hijack primitives beyond the immediate hash-buffer access.\nA:H - Concurrent UAF read of freed conn-\u003epreauth_info during smb3_preauth_hash_rsp() causes kernel oops or panic (KASAN-confirmed); even without full exploitation the race reliably triggers high-severity denial of service on the server."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-17T05:44:02.758Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/c7bef84740d1d57848c74f6f5b996606e43ea4fe"
},
{
"url": "https://git.kernel.org/stable/c/d0a469122e7bf8338fec1949fb1e8e1290ed8caa"
},
{
"url": "https://git.kernel.org/stable/c/7470511d085af1c7a043a60e53d52b512d5a10b1"
},
{
"url": "https://git.kernel.org/stable/c/16a1ecf39c217e3d164bd32ef2a4f650abc067fa"
},
{
"url": "https://git.kernel.org/stable/c/77bb0bbfcc4e777ca653174689e5e363f8ee63d1"
},
{
"url": "https://git.kernel.org/stable/c/1c89da3baa2b1f269178afa87dc30479b8535776"
},
{
"url": "https://git.kernel.org/stable/c/0c054227479ed7e36ebccb3a558bc0ef698264f6"
}
],
"title": "ksmbd: fix use-after-free of conn-\u003epreauth_info in concurrent SMB2 NEGOTIATE",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-72422",
"datePublished": "2026-08-15T05:56:41.090Z",
"dateReserved": "2026-08-09T03:40:39.927Z",
"dateUpdated": "2026-08-17T05:44:02.758Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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