CVE-2026-53390 (GCVE-0-2026-53390)
Vulnerability from cvelistv5 – Published: 2026-07-19 12:01 – Updated: 2026-08-17 04:50
VLAI
EPSS
VEX
Title
ksmbd: fix out-of-bounds read in smb_check_perm_dacl()
Summary
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix out-of-bounds read in smb_check_perm_dacl()
The permission-check ACE walk in smb_check_perm_dacl() validates the ACE
header size and caps sid.num_subauth at SID_MAX_SUB_AUTHORITIES, but it
never checks that ace->size is actually large enough to contain
num_subauth sub-authorities before compare_sids() dereferences them.
CIFS_SID_BASE_SIZE covers the SID header up to but excluding the
sub_auth[] array, and offsetof(struct smb_ace, sid) is the ACE header,
so the existing guards only guarantee the 8-byte SID base, i.e. zero
sub-authorities. compare_sids() then reads ace->sid.sub_auth[i] for
i < min(local_sid->num_subauth, ace->sid.num_subauth). The local
comparison SIDs (sid_everyone, sid_unix_NFS_mode, and the id_to_sid()
result) always have at least one sub-authority, and an attacker controls
the ACE revision and authority bytes (which lie within the in-bounds SID
base), so they can match one of those SIDs and force the sub_auth read.
A crafted ACE with size == 16 and num_subauth >= 1 placed at the tail of
the security descriptor therefore causes a heap out-of-bounds read of up
to SID_MAX_SUB_AUTHORITIES * sizeof(__le32) bytes past the pntsd
allocation. The security descriptor is loaded by ksmbd_vfs_get_sd_xattr()
into a buffer sized exactly to the on-disk data (kzalloc(sd_size) in
ndr_decode_v4_ntacl()), so the read lands past the allocation. The
malformed descriptor can be stored verbatim via SMB2_SET_INFO (the DACL
is not normalised before being written to the security.NTACL xattr) and
the read fires on a subsequent SMB2_CREATE access check, making this
reachable by an authenticated client on a share that uses ACL xattrs.
Add the missing num_subauth-versus-ace_size check, mirroring the
identical guards already present in the sibling parsers parse_dacl() and
smb_inherit_dacl().
Severity
8.1 (High)
Assigner
References
7 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
282cbbb476b9f35793452bc461934af4c7eca169 , < c7488c85fd822959e9b5c22fbd9e7c8a21caf5e0
(git)
Affected: f20adc4ef7428bc485ee83fd1a592252fb87718b , < 988c93d3bba066d8669143e6ec30bb2be9608d53 (git) Affected: 325d4ac11f526cb8964cff14548ccf02d8c756d8 , < 36599894fa8536fefdf1e296c0af71b8b7226859 (git) Affected: 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c , < d5c81a095c86fe507c032d08f3a8cfc518444927 (git) Affected: 90089584b2e25c4510b7b987387b4405f0673ece , < 7627ff8c4f9919f14de562b0160ab4ec9d80b1f7 (git) Affected: d07b26f39246a82399661936dd0c853983cfade7 , < e36e35660adb9b8ef1435ac359151dda5f094c55 (git) Affected: d07b26f39246a82399661936dd0c853983cfade7 , < 1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b (git) Affected: 151b1799861fde38087c08f613abc2843ef597b0 (git) Affected: 5.15.210 , < 5.15.212 (semver) Affected: 6.1.176 , < 6.1.177 (semver) Affected: 6.6.140 , < 6.6.144 (semver) Affected: 6.12.84 , < 6.12.95 (semver) Affected: 6.18.25 , < 6.18.38 (semver) Affected: 7.0.2 , < 7.1 (semver) |
guessed | |
| Linux | Linux |
Affected:
7.1
Unaffected: 0 , < 7.1 (semver) Unaffected: 5.15.212 , ≤ 5.15.* (semver) Unaffected: 6.1.177 , ≤ 6.1.* (semver) Unaffected: 6.6.144 , ≤ 6.6.* (semver) Unaffected: 6.12.95 , ≤ 6.12.* (semver) Unaffected: 6.18.38 , ≤ 6.18.* (semver) Unaffected: 7.1.3 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix) |
guessed |
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix out-of-bounds read in smb_check_perm_dacl()\n\nThe permission-check ACE walk in smb_check_perm_dacl() validates the ACE\nheader size and caps sid.num_subauth at SID_MAX_SUB_AUTHORITIES, but it\nnever checks that ace-\u003esize is actually large enough to contain\nnum_subauth sub-authorities before compare_sids() dereferences them.\n\nCIFS_SID_BASE_SIZE covers the SID header up to but excluding the\nsub_auth[] array, and offsetof(struct smb_ace, sid) is the ACE header,\nso the existing guards only guarantee the 8-byte SID base, i.e. zero\nsub-authorities. compare_sids() then reads ace-\u003esid.sub_auth[i] for\ni \u003c min(local_sid-\u003enum_subauth, ace-\u003esid.num_subauth). The local\ncomparison SIDs (sid_everyone, sid_unix_NFS_mode, and the id_to_sid()\nresult) always have at least one sub-authority, and an attacker controls\nthe ACE revision and authority bytes (which lie within the in-bounds SID\nbase), so they can match one of those SIDs and force the sub_auth read.\n\nA crafted ACE with size == 16 and num_subauth \u003e= 1 placed at the tail of\nthe security descriptor therefore causes a heap out-of-bounds read of up\nto SID_MAX_SUB_AUTHORITIES * sizeof(__le32) bytes past the pntsd\nallocation. The security descriptor is loaded by ksmbd_vfs_get_sd_xattr()\ninto a buffer sized exactly to the on-disk data (kzalloc(sd_size) in\nndr_decode_v4_ntacl()), so the read lands past the allocation. The\nmalformed descriptor can be stored verbatim via SMB2_SET_INFO (the DACL\nis not normalised before being written to the security.NTACL xattr) and\nthe read fires on a subsequent SMB2_CREATE access check, making this\nreachable by an authenticated client on a share that uses ACL xattrs.\n\nAdd the missing num_subauth-versus-ace_size check, mirroring the\nidentical guards already present in the sibling parsers parse_dacl() and\nsmb_inherit_dacl()."
}
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"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
"version": "3.1"
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"lang": "en",
"value": "AV:N - The bug is reachable through ksmbd\u0027s in-kernel SMB2 server on TCP/445 via SMB2_SET_INFO (to store a crafted security descriptor) and SMB2_CREATE (to trigger the DACL walk), with packets handled from ksmbd_conn_handler_loop() through smb2_set_info()/smb2_open() into smb_check_perm_dacl().\nAC:L - An attacker fully controls the malformed ACE fields (size, num_subauth, revision, authority bytes) and can reliably place the ACE at the tail of a security descriptor, store it verbatim, then trigger the read on the next CREATE without depending on race timing or uncontrollable memory layout.\nPR:L - Exploitation requires a completed SMB2 session and share access: SMB2_SET_INFO needs FILE_WRITE_DAC/FILE_WRITE_OWNER on an open file, and the poisoned descriptor is only persisted on shares with ACL xattr support, which is authenticated low-privilege client access rather than pre-auth or host root.\nUI:N - No end-user action is required beyond the attacker sending crafted SMB2 protocol messages over the network; no victim must open a file, mount a share, or perform any interactive step.\nS:U - The vulnerability is confined to kernel heap memory reads during ksmbd DACL permission evaluation and does not cross a security boundary such as guest-to-host VM escape or sandbox escape.\nC:H - compare_sids() performs a heap out-of-bounds read of up to SID_MAX_SUB_AUTHORITIES (15) sub-authority dwords (60 bytes) past the kzalloc()-sized security descriptor buffer, exposing adjacent kernel heap contents even though the data is not returned in the SMB response.\nI:N - The flaw is a read-only out-of-bounds access in compare_sids() with no memory write, type confusion, or demonstrated control-flow hijack primitive; integrity is not directly compromised.\nA:H - Reading past the end of the kmalloc allocation can fault the kernel (oops/panic), and a malicious descriptor planted on a shared file can deny availability to any other authenticated client whose SMB2_CREATE triggers smb_check_perm_dacl()."
}
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"title": "ksmbd: fix out-of-bounds read in smb_check_perm_dacl()",
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{
"criteria": "cpe:2.3:o:linux:linux_kernel:6.1.176:*:*:*:*:*:*:*",
"matchCriteriaId": "31ED607F-61AA-41F2-B79C-959EDFA61657",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix out-of-bounds read in smb_check_perm_dacl()\n\nThe permission-check ACE walk in smb_check_perm_dacl() validates the ACE\nheader size and caps sid.num_subauth at SID_MAX_SUB_AUTHORITIES, but it\nnever checks that ace-\u003esize is actually large enough to contain\nnum_subauth sub-authorities before compare_sids() dereferences them.\n\nCIFS_SID_BASE_SIZE covers the SID header up to but excluding the\nsub_auth[] array, and offsetof(struct smb_ace, sid) is the ACE header,\nso the existing guards only guarantee the 8-byte SID base, i.e. zero\nsub-authorities. compare_sids() then reads ace-\u003esid.sub_auth[i] for\ni \u003c min(local_sid-\u003enum_subauth, ace-\u003esid.num_subauth). The local\ncomparison SIDs (sid_everyone, sid_unix_NFS_mode, and the id_to_sid()\nresult) always have at least one sub-authority, and an attacker controls\nthe ACE revision and authority bytes (which lie within the in-bounds SID\nbase), so they can match one of those SIDs and force the sub_auth read.\n\nA crafted ACE with size == 16 and num_subauth \u003e= 1 placed at the tail of\nthe security descriptor therefore causes a heap out-of-bounds read of up\nto SID_MAX_SUB_AUTHORITIES * sizeof(__le32) bytes past the pntsd\nallocation. The security descriptor is loaded by ksmbd_vfs_get_sd_xattr()\ninto a buffer sized exactly to the on-disk data (kzalloc(sd_size) in\nndr_decode_v4_ntacl()), so the read lands past the allocation. The\nmalformed descriptor can be stored verbatim via SMB2_SET_INFO (the DACL\nis not normalised before being written to the security.NTACL xattr) and\nthe read fires on a subsequent SMB2_CREATE access check, making this\nreachable by an authenticated client on a share that uses ACL xattrs.\n\nAdd the missing num_subauth-versus-ace_size check, mirroring the\nidentical guards already present in the sibling parsers parse_dacl() and\nsmb_inherit_dacl()."
}
],
"id": "CVE-2026-53390",
"lastModified": "2026-08-17T05:17:13.293",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 8.1,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "NONE",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
"version": "3.1"
},
"exploitabilityScore": 2.8,
"impactScore": 5.2,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
]
},
"published": "2026-07-19T12:16:50.000",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/36599894fa8536fefdf1e296c0af71b8b7226859"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/7627ff8c4f9919f14de562b0160ab4ec9d80b1f7"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/988c93d3bba066d8669143e6ec30bb2be9608d53"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/c7488c85fd822959e9b5c22fbd9e7c8a21caf5e0"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/d5c81a095c86fe507c032d08f3a8cfc518444927"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/e36e35660adb9b8ef1435ac359151dda5f094c55"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Analyzed",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-125"
}
],
"source": "nvd@nist.gov",
"type": "Primary"
}
]
}
},
"redhat_vex": {
"aggregate_severity": "None",
"current_release_date": "2026-07-21T08:02:56+00:00",
"cve": "CVE-2026-53390",
"id": "CVE-2026-53390",
"initial_release_date": "2026-07-19T00:00:00+00:00",
"product_status:known_not_affected": "275",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: ksmbd: fix out-of-bounds read in smb_check_perm_dacl()",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-53390.json",
"version": "3"
},
"suse_vex": {
"aggregate_severity": "important",
"current_release_date": "2026-07-21T13:06:53Z",
"cve": "CVE-2026-53390",
"id": "CVE-2026-53390",
"initial_release_date": "2026-07-19T17:36:06Z",
"product_status:known_not_affected": "284",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2026-53390",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-53390.json",
"version": "3"
}
}
}
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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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