CVE-2026-89788 (GCVE-0-2026-89788)
Vulnerability from cvelistv5 – Published: 2026-09-16 08:48 – Updated: 2026-09-16 14:38
VLAI
EPSS
VEX
Title
ksmbd: fix tree connection use-after-free in smb2_tree_connect()
Summary
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix tree connection use-after-free in smb2_tree_connect()
ksmbd_tree_conn_connect() publishes a new tree connection in
sess->tree_conns with a single reference and returns its pointer to
smb2_tree_connect(). The handler continues to initialize the object and
build the response after publication. A concurrent session logoff can
erase the connection and drop that reference, freeing the object while
the handler still uses it.
BUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90
smb2_tree_connect (fs/smb/server/smb2pdu.c:2872)
handle_ksmbd_work
process_one_work
worker_thread
kthread
After xa_store() succeeds, take a second reference before releasing
tree_conns_lock. The original reference belongs to the xarray entry and
the second belongs to the creating smb2_tree_connect() handler.
Keep the references balanced in every path:
- On normal exit or an error after publication, smb2_tree_connect()
drops its creator reference. Error cleanup also calls
ksmbd_tree_conn_disconnect(), which drops the xarray reference only if
it removes the exact entry.
- SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop
its xarray reference. The request's existing lookup reference remains
owned by the request and is released by the existing cleanup.
- Session LOGOFF removes each entry and drops its xarray reference. If
it wins the race, later cleanup sees that the entry is gone and does
not drop that reference again.
To enforce this ownership, claim the disconnected state and erase the
exact entry atomically under tree_conns_lock. This guarantees one drop
for the xarray reference and one drop by each in-flight user, regardless
of which teardown path wins. If logoff removes the entry before
initialization completes, fail the connect instead of marking the
detached object TREE_CONNECTED.
Severity
9.8 (Critical)
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
33b235a6e6ebe0f05f3586a71e8d281d00f71e2e , < 4e30fbd26e84efa2e5cbec4eb11e126ac0c79313
(git)
Affected: 33b235a6e6ebe0f05f3586a71e8d281d00f71e2e , < b5ec6c462aab1062cf5d1e667ba7c6442f737055 (git) Affected: dd45db4d9bbc8f122a9b4db5ce94ae29fcf03d3c (git) Affected: 7b58ee8d0b91359554cf219cd4f33872ea2afd66 (git) Affected: 5.15.145 , < 5.16 (semver) Affected: 6.1.71 , < 6.2 (semver) |
guessed | |
| Linux | Linux |
Affected:
6.6
Unaffected: 0 , < 6.6 (semver) Unaffected: 7.2.6 , ≤ 7.2.* (semver) Unaffected: 7.3-rc2 , ≤ * (original_commit_for_fix) |
guessed |
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/smb/server/mgmt/tree_connect.c",
"fs/smb/server/smb2pdu.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "4e30fbd26e84efa2e5cbec4eb11e126ac0c79313",
"status": "affected",
"version": "33b235a6e6ebe0f05f3586a71e8d281d00f71e2e",
"versionType": "git"
},
{
"lessThan": "b5ec6c462aab1062cf5d1e667ba7c6442f737055",
"status": "affected",
"version": "33b235a6e6ebe0f05f3586a71e8d281d00f71e2e",
"versionType": "git"
},
{
"status": "affected",
"version": "dd45db4d9bbc8f122a9b4db5ce94ae29fcf03d3c",
"versionType": "git"
},
{
"status": "affected",
"version": "7b58ee8d0b91359554cf219cd4f33872ea2afd66",
"versionType": "git"
},
{
"lessThan": "5.16",
"status": "affected",
"version": "5.15.145",
"versionType": "semver"
},
{
"lessThan": "6.2",
"status": "affected",
"version": "6.1.71",
"versionType": "semver"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/smb/server/mgmt/tree_connect.c",
"fs/smb/server/smb2pdu.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "6.6"
},
{
"lessThan": "6.6",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.2.*",
"status": "unaffected",
"version": "7.2.6",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.3-rc2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.2.6",
"versionStartIncluding": "6.6",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.3-rc2",
"versionStartIncluding": "6.6",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.15.145",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "6.1.71",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix tree connection use-after-free in smb2_tree_connect()\n\nksmbd_tree_conn_connect() publishes a new tree connection in\nsess-\u003etree_conns with a single reference and returns its pointer to\nsmb2_tree_connect(). The handler continues to initialize the object and\nbuild the response after publication. A concurrent session logoff can\nerase the connection and drop that reference, freeing the object while\nthe handler still uses it.\n\nBUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90\n smb2_tree_connect (fs/smb/server/smb2pdu.c:2872)\n handle_ksmbd_work\n process_one_work\n worker_thread\n kthread\n\nAfter xa_store() succeeds, take a second reference before releasing\ntree_conns_lock. The original reference belongs to the xarray entry and\nthe second belongs to the creating smb2_tree_connect() handler.\n\nKeep the references balanced in every path:\n\n- On normal exit or an error after publication, smb2_tree_connect()\n drops its creator reference. Error cleanup also calls\n ksmbd_tree_conn_disconnect(), which drops the xarray reference only if\n it removes the exact entry.\n- SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop\n its xarray reference. The request\u0027s existing lookup reference remains\n owned by the request and is released by the existing cleanup.\n- Session LOGOFF removes each entry and drops its xarray reference. If\n it wins the race, later cleanup sees that the entry is gone and does\n not drop that reference again.\n\nTo enforce this ownership, claim the disconnected state and erase the\nexact entry atomically under tree_conns_lock. This guarantees one drop\nfor the xarray reference and one drop by each in-flight user, regardless\nof which teardown path wins. If logoff removes the entry before\ninitialization completes, fail the connect instead of marking the\ndetached object TREE_CONNECTED."
}
],
"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 - ksmbd is the in-kernel SMB server on TCP/445; the UAF is reached from remote SMB2 TREE_CONNECT racing SESSION_LOGOFF via ksmbd_conn_handler_loop() through handle_ksmbd_work(), smb2_tree_connect(), ksmbd_tree_conn_connect(), and ksmbd_tree_conn_session_logoff().\nAC:L - The attacker drives both sides by issuing concurrent SMB2 TREE_CONNECT and SESSION_LOGOFF on their own connections (SMB3 multi-channel or parallel ksmbd-io work items). After xa_store() the object has one xarray ref, so logoff can free it while the handler still uses it; no victim timing or rare kernel config is required.\nPR:N - TREE_CONNECT and LOGOFF need a valid SMB2 session, but ksmbd supports guest/anonymous users and guest-ok shares (including IPC$); guest session setup skips NTLMSSP password verification, so a reasonable NAS/IoT deployment lets an unauthenticated client reach this path.\nUI:N - No victim action is required; the attacker programmatically issues SESSION_SETUP, TREE_CONNECT, and LOGOFF on their own SMB connections to trigger the race.\nS:U - The UAF corrupts ksmbd/kernel heap on the SMB server host and can escalate privileges within that kernel; it does not cross a VM, guest-to-host, container, or IOMMU/DMA security boundary.\nC:H - Use-after-free of struct ksmbd_tree_connect and its share_conf pointer: after logoff kfree\u0027s the published object, smb2_tree_connect still reads share flags and fields, enabling arbitrary kernel disclosure via heap reuse.\nI:H - The handler writes t_state, maximal_access, and posix_extensions into the freed object after xa_store(); with heap spray this yields arbitrary kernel writes and control-flow hijacking, matching High integrity for tree_conn UAF.\nA:H - KASAN reports slab-use-after-free in smb2_tree_connect on the ksmbd-io worker; the dangling tree_conn pointer causes a kernel oops or panic and is repeatable by resending TREE_CONNECT concurrently with LOGOFF."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-16T14:38:37.595Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/4e30fbd26e84efa2e5cbec4eb11e126ac0c79313"
},
{
"url": "https://git.kernel.org/stable/c/b5ec6c462aab1062cf5d1e667ba7c6442f737055"
}
],
"title": "ksmbd: fix tree connection use-after-free in smb2_tree_connect()",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-89788",
"datePublished": "2026-09-16T08:48:25.049Z",
"dateReserved": "2026-09-11T19:38:34.766Z",
"dateUpdated": "2026-09-16T14:38:37.595Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-89788",
"date": "2026-09-16",
"epss": "0.00189",
"percentile": "0.08779"
},
"microsoft_vex": {
"current_release_date": "2026-09-17T01:03:38.000Z",
"cve": "CVE-2026-89788",
"id": "msrc_CVE-2026-89788",
"initial_release_date": "2026-09-17T01:03:38.000Z",
"product_status:known_affected": "1",
"source": "Microsoft CSAF VEX",
"status": "final",
"title": "ksmbd: fix tree connection use-after-free in smb2_tree_connect()",
"url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-89788.json",
"version": "1"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2026-89788\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-09-16T09:17:09.590\",\"lastModified\":\"2026-09-16T15:18:09.007\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nksmbd: fix tree connection use-after-free in smb2_tree_connect()\\n\\nksmbd_tree_conn_connect() publishes a new tree connection in\\nsess-\u003etree_conns with a single reference and returns its pointer to\\nsmb2_tree_connect(). The handler continues to initialize the object and\\nbuild the response after publication. A concurrent session logoff can\\nerase the connection and drop that reference, freeing the object while\\nthe handler still uses it.\\n\\nBUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90\\n smb2_tree_connect (fs/smb/server/smb2pdu.c:2872)\\n handle_ksmbd_work\\n process_one_work\\n worker_thread\\n kthread\\n\\nAfter xa_store() succeeds, take a second reference before releasing\\ntree_conns_lock. The original reference belongs to the xarray entry and\\nthe second belongs to the creating smb2_tree_connect() handler.\\n\\nKeep the references balanced in every path:\\n\\n- On normal exit or an error after publication, smb2_tree_connect()\\n drops its creator reference. Error cleanup also calls\\n ksmbd_tree_conn_disconnect(), which drops the xarray reference only if\\n it removes the exact entry.\\n- SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop\\n its xarray reference. The request\u0027s existing lookup reference remains\\n owned by the request and is released by the existing cleanup.\\n- Session LOGOFF removes each entry and drops its xarray reference. If\\n it wins the race, later cleanup sees that the entry is gone and does\\n not drop that reference again.\\n\\nTo enforce this ownership, claim the disconnected state and erase the\\nexact entry atomically under tree_conns_lock. This guarantees one drop\\nfor the xarray reference and one drop by each in-flight user, regardless\\nof which teardown path wins. If logoff removes the entry before\\ninitialization completes, fail the connect instead of marking the\\ndetached object TREE_CONNECTED.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/smb/server/mgmt/tree_connect.c\",\"fs/smb/server/smb2pdu.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"33b235a6e6ebe0f05f3586a71e8d281d00f71e2e\",\"lessThan\":\"4e30fbd26e84efa2e5cbec4eb11e126ac0c79313\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"33b235a6e6ebe0f05f3586a71e8d281d00f71e2e\",\"lessThan\":\"b5ec6c462aab1062cf5d1e667ba7c6442f737055\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"dd45db4d9bbc8f122a9b4db5ce94ae29fcf03d3c\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"7b58ee8d0b91359554cf219cd4f33872ea2afd66\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5.15.145\",\"lessThan\":\"5.16\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"6.1.71\",\"lessThan\":\"6.2\",\"versionType\":\"semver\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/smb/server/mgmt/tree_connect.c\",\"fs/smb/server/smb2pdu.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"6.6\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.6\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2.6\",\"lessThanOrEqual\":\"7.2.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.3-rc2\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/4e30fbd26e84efa2e5cbec4eb11e126ac0c79313\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/b5ec6c462aab1062cf5d1e667ba7c6442f737055\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
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.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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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.
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