CVE-2026-99109 (GCVE-0-2026-99109)

Vulnerability from cvelistv5 – Published: 2026-10-28 10:34 – Updated: 2026-11-06 17:15
VLAI
Title
smb: client: reject SetEA requests that do not fit the request buffer
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: reject SetEA requests that do not fit the request buffer CIFSSMBSetEA() copies the caller's extended attribute value into the SMB request buffer without checking that it fits. The requirement is stated in the source but was never implemented: /*BB add length check to see if it would fit in negotiated SMB buffer size BB */ /* if (ea_value_len > buffer_size - 512 (enough for header)) */ if (ea_value_len) memcpy(parm_data->list.name + name_len + 1, ea_value, ea_value_len); The only bound applied on the way in is in cifs_xattr_set(): #define MAX_EA_VALUE_SIZE CIFSMaxBufSize ... if (size > MAX_EA_VALUE_SIZE) CIFSMaxBufSize is the full payload capacity of the buffer, so a value of exactly that size leaves no room for the SMB header, the TRANS2 parameter block, the fealist header and the EA name that are written ahead of it in the same object. SendReceive() already enforces the correct limit on this very length: if (in_len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE) but it is called after the copy has taken place. An unprivileged setxattr(2) on an SMB1 mount with a 250-byte name and a 16384-byte value writes 16384 bytes starting 345 bytes into a 16588-byte cifs_request object, ending 141 bytes past it: BUG: KASAN: slab-out-of-bounds in CIFSSMBSetEA+0xabc/0xde0 Write of size 16384 at addr ffff888003aa0159 by task init/68 __asan_memcpy+0x3c/0x60 CIFSSMBSetEA+0xabc/0xde0 cifs_xattr_set+0xd3a/0xff0 __vfs_setxattr+0x13e/0x1a0 The buggy address is located 345 bytes inside of allocated 16588-byte region Apply SendReceive()'s limit to the assembled request before the copy rather than after it, and widen the byte counters so the sum cannot wrap before it is tested. byte_count is also tested against U16_MAX, because it is stored in the 16-bit pSMB->ByteCount. That becomes reachable when CIFSMaxBufSize is raised at module load, where it may be set as high as 1024*127: with a 5-byte EA name and a 65521-byte value, count is exactly U16_MAX while byte_count is 65556, and cpu_to_le16() would truncate it to 20 and transmit a frame whose ByteCount does not match its length. Testing byte_count covers count as well, since byte_count is the larger of the two and count's only 16-bit consumer is written after this point. check_add_overflow() is evaluated first so that total_len is assigned before it is reported.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6653 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 79345a5d14b851e9ed28d3a9fe53301661dbcf11 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 9efbd764ab80fa86d2258550877a74d78a25e855 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 4aa2c106aef4bf3dfd97c30842db0767b26e8428 (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 6.18.61 , ≤ 6.18.* (semver)
Unaffected: 7.2.13 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: reject SetEA requests that do not fit the request buffer\n\nCIFSSMBSetEA() copies the caller\u0027s extended attribute value into the\nSMB request buffer without checking that it fits.  The requirement is\nstated in the source but was never implemented:\n\n\t/*BB add length check to see if it would fit in\n\t     negotiated SMB buffer size BB */\n\t/* if (ea_value_len \u003e buffer_size - 512 (enough for header)) */\n\tif (ea_value_len)\n\t\tmemcpy(parm_data-\u003elist.name + name_len + 1,\n\t\t       ea_value, ea_value_len);\n\nThe only bound applied on the way in is in cifs_xattr_set():\n\n\t#define MAX_EA_VALUE_SIZE CIFSMaxBufSize\n\t...\n\tif (size \u003e MAX_EA_VALUE_SIZE)\n\nCIFSMaxBufSize is the full payload capacity of the buffer, so a value\nof exactly that size leaves no room for the SMB header, the TRANS2\nparameter block, the fealist header and the EA name that are written\nahead of it in the same object.\n\nSendReceive() already enforces the correct limit on this very length:\n\n\tif (in_len \u003e CIFSMaxBufSize + MAX_CIFS_HDR_SIZE)\n\nbut it is called after the copy has taken place.  An unprivileged\nsetxattr(2) on an SMB1 mount with a 250-byte name and a 16384-byte\nvalue writes 16384 bytes starting 345 bytes into a 16588-byte\ncifs_request object, ending 141 bytes past it:\n\n  BUG: KASAN: slab-out-of-bounds in CIFSSMBSetEA+0xabc/0xde0\n  Write of size 16384 at addr ffff888003aa0159 by task init/68\n   __asan_memcpy+0x3c/0x60\n   CIFSSMBSetEA+0xabc/0xde0\n   cifs_xattr_set+0xd3a/0xff0\n   __vfs_setxattr+0x13e/0x1a0\n  The buggy address is located 345 bytes inside of\n   allocated 16588-byte region\n\nApply SendReceive()\u0027s limit to the assembled request before the copy\nrather than after it, and widen the byte counters so the sum cannot\nwrap before it is tested.\n\nbyte_count is also tested against U16_MAX, because it is stored in the\n16-bit pSMB-\u003eByteCount.  That becomes reachable when CIFSMaxBufSize is\nraised at module load, where it may be set as high as 1024*127: with a\n5-byte EA name and a 65521-byte value, count is exactly U16_MAX while\nbyte_count is 65556, and cpu_to_le16() would truncate it to 20 and\ntransmit a frame whose ByteCount does not match its length.  Testing\nbyte_count covers count as well, since byte_count is the larger of the\ntwo and count\u0027s only 16-bit consumer is written after this point.\n\ncheck_add_overflow() is evaluated first so that total_len is assigned\nbefore it is reported."
        }
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "lang": "en",
              "value": "AV:L - The attacker-controlled bytes originate in setxattr(2): path_setxattrat() copies the local value, then cifs_xattr_set() calls SMB1\u0027s CIFSSMBSetEA(), whose memcpy overflows the request before any SMB response is processed.\nAC:L - On an existing vers=1.0 mount, the caller can deterministically choose a user.* suffix up to 250 bytes and a value up to CIFSMaxBufSize; CIFSSMBSetEA() performs the oversized memcpy before SendReceive() checks in_len, with no race or server-controlled condition.\nPR:L - vfs_setxattr() calls xattr_permission() with MAY_WRITE, and a user.* attribute requires only write permission on the CIFS inode; although creating the mount requires init-namespace CAP_SYS_ADMIN, exploiting an existing writable mount requires no capability.\nUI:N - The attacker invokes setxattr(2) themselves on a writable file in the already-mounted share; no other user must open a file, approve a prompt, or perform a mount during exploitation.\nS:U - The overwrite occurs in the client kernel\u0027s cifs_request allocation returned by cifs_buf_get() and affects that same kernel security authority, without crossing a VM, IOMMU, or sandbox boundary.\nC:H - CIFSSMBSetEA() copies attacker-chosen ea_value bytes beyond the cifs_request object; grooming concurrent allocations can turn corruption of adjacent request or allocator state into control-flow execution and arbitrary kernel-memory disclosure.\nI:H - The vulnerable memcpy provides a contiguous attacker-controlled heap overwrite; the reproduced 16384-byte copy starts at offset 345 and ends 141 bytes beyond the 16588-byte cifs_request, enabling adjacent-object corruption and control-flow hijacking.\nA:H - The reproduced setxattr(2) triggers a KASAN slab-out-of-bounds fault in CIFSSMBSetEA(); hitting guarded memory or corrupting request or allocator state can oops or panic the kernel, and the caller can repeat the syscall."
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        "dateUpdated": "2026-11-06T17:15:07.205Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-99109",
    "datePublished": "2026-10-28T10:34:27.507Z",
    "dateReserved": "2026-09-25T10:25:14.391Z",
    "dateUpdated": "2026-11-06T17:15:07.205Z",
    "state": "PUBLISHED"
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  "dataVersion": "5.2",
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      "date": "2026-11-07",
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      "percentile": "0.03128"
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      "cve": "CVE-2026-99109",
      "id": "msrc_CVE-2026-99109",
      "initial_release_date": "2026-10-29T01:03:31.000Z",
      "product_status:known_affected": "3",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "smb: client: reject SetEA requests that do not fit the request buffer",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-99109.json",
      "version": "3"
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: reject SetEA requests that do not fit the request buffer\n\nCIFSSMBSetEA() copies the caller\u0027s extended attribute value into the\nSMB request buffer without checking that it fits.  The requirement is\nstated in the source but was never implemented:\n\n\t/*BB add length check to see if it would fit in\n\t     negotiated SMB buffer size BB */\n\t/* if (ea_value_len \u003e buffer_size - 512 (enough for header)) */\n\tif (ea_value_len)\n\t\tmemcpy(parm_data-\u003elist.name + name_len + 1,\n\t\t       ea_value, ea_value_len);\n\nThe only bound applied on the way in is in cifs_xattr_set():\n\n\t#define MAX_EA_VALUE_SIZE CIFSMaxBufSize\n\t...\n\tif (size \u003e MAX_EA_VALUE_SIZE)\n\nCIFSMaxBufSize is the full payload capacity of the buffer, so a value\nof exactly that size leaves no room for the SMB header, the TRANS2\nparameter block, the fealist header and the EA name that are written\nahead of it in the same object.\n\nSendReceive() already enforces the correct limit on this very length:\n\n\tif (in_len \u003e CIFSMaxBufSize + MAX_CIFS_HDR_SIZE)\n\nbut it is called after the copy has taken place.  An unprivileged\nsetxattr(2) on an SMB1 mount with a 250-byte name and a 16384-byte\nvalue writes 16384 bytes starting 345 bytes into a 16588-byte\ncifs_request object, ending 141 bytes past it:\n\n  BUG: KASAN: slab-out-of-bounds in CIFSSMBSetEA+0xabc/0xde0\n  Write of size 16384 at addr ffff888003aa0159 by task init/68\n   __asan_memcpy+0x3c/0x60\n   CIFSSMBSetEA+0xabc/0xde0\n   cifs_xattr_set+0xd3a/0xff0\n   __vfs_setxattr+0x13e/0x1a0\n  The buggy address is located 345 bytes inside of\n   allocated 16588-byte region\n\nApply SendReceive()\u0027s limit to the assembled request before the copy\nrather than after it, and widen the byte counters so the sum cannot\nwrap before it is tested.\n\nbyte_count is also tested against U16_MAX, because it is stored in the\n16-bit pSMB-\u003eByteCount.  That becomes reachable when CIFSMaxBufSize is\nraised at module load, where it may be set as high as 1024*127: with a\n5-byte EA name and a 65521-byte value, count is exactly U16_MAX while\nbyte_count is 65556, and cpu_to_le16() would truncate it to 20 and\ntransmit a frame whose ByteCount does not match its length.  Testing\nbyte_count covers count as well, since byte_count is the larger of the\ntwo and count\u0027s only 16-bit consumer is written after this point.\n\ncheck_add_overflow() is evaluated first so that total_len is assigned\nbefore it is reported."
          }
        ],
        "id": "CVE-2026-99109",
        "lastModified": "2026-11-06T18:18:31.847",
        "metrics": {
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                "attackVector": "LOCAL",
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                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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        "published": "2026-10-28T11:17:30.287",
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        "vulnStatus": "Received"
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-11-05T00:25:09+00:00",
      "cve": "CVE-2026-99109",
      "id": "CVE-2026-99109",
      "initial_release_date": "2026-10-28T00:00:00+00:00",
      "product_status:known_affected": "161",
      "product_status:known_not_affected": "42",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: smb: client: reject SetEA requests that do not fit the request buffer",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-99109.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-11-01T00:38:39Z",
      "cve": "CVE-2026-99109",
      "id": "CVE-2026-99109",
      "initial_release_date": "2026-10-28T17:34:55Z",
      "product_status:known_affected": "205",
      "product_status:known_not_affected": "143",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-99109",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-99109.json",
      "version": "4"
    }
  }
}



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