CVE-2026-97926 (GCVE-0-2026-97926)

Vulnerability from cvelistv5 – Published: 2026-09-25 10:22 – Updated: 2026-09-25 14:41
VLAI
Title
ufs: validate cylinder group metadata before caching it
Summary
In the Linux kernel, the following vulnerability has been resolved: ufs: validate cylinder group metadata before caching it ufs_read_cylinder() copies the cylinder group index and the rotor positions straight from the on-disk group and caches them without any check: ucpi->c_cgx = fs32_to_cpu(sb, ucg->cg_cgx); ucpi->c_rotor = fs32_to_cpu(sb, ucg->cg_rotor); ucpi->c_frotor = fs32_to_cpu(sb, ucg->cg_frotor); ucpi->c_irotor = fs32_to_cpu(sb, ucg->cg_irotor); They are then used as indices during allocation and free: - c_cgx indexes the cylinder summary array as UFS_SB(sb)->fs_cs(ucpi->c_cgx), so a value past s_ncg writes a 32 bit count outside the s_csp allocation. - c_frotor becomes a bitmap scan start, start = c_frotor >> 3, and then length = ((s_fpg + 7) >> 3) - start. A start beyond the block bitmap wraps the unsigned length to a huge value, so ubh_scanc() walks far past the cylinder group buffers. c_irotor drives the inode bitmap the same way. A crafted image can set any of these freely, turning an ordinary allocation into an out of bounds access. Reject a cylinder group whose recorded index does not match the group being read, or whose rotors fall outside the group, before the metadata is cached. Valid filesystems keep cg_cgx equal to the group number and the rotors within the group, so only malformed images are rejected.
Severity
7 (High)
CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 5902a95066883cf96fa15b2680694fc5dd0c7d11 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 87b12dc360a002eb2d498aa4f01e84347019612d (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < abde9eb33106850dfa367ad3965d3588bb8558d5 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < c9d263be26806d388129fab8c6904bed197fc6af (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 6.12.111 , ≤ 6.12.* (semver)
Unaffected: 6.18.53 , ≤ 6.18.* (semver)
Unaffected: 7.2.7 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc3 , ≤ * (original_commit_for_fix)
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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ufs/cylinder.c"
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          "programFiles": [
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          "vendor": "Linux",
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              "versionType": "semver"
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              "versionType": "semver"
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
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                  "versionEndExcluding": "6.12.111",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                },
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.53",
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                  "vulnerable": true
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nufs: validate cylinder group metadata before caching it\n\nufs_read_cylinder() copies the cylinder group index and the rotor\npositions straight from the on-disk group and caches them without any\ncheck:\n\n\tucpi-\u003ec_cgx    = fs32_to_cpu(sb, ucg-\u003ecg_cgx);\n\tucpi-\u003ec_rotor  = fs32_to_cpu(sb, ucg-\u003ecg_rotor);\n\tucpi-\u003ec_frotor = fs32_to_cpu(sb, ucg-\u003ecg_frotor);\n\tucpi-\u003ec_irotor = fs32_to_cpu(sb, ucg-\u003ecg_irotor);\n\nThey are then used as indices during allocation and free:\n\n  - c_cgx indexes the cylinder summary array as\n    UFS_SB(sb)-\u003efs_cs(ucpi-\u003ec_cgx), so a value past s_ncg writes a 32\n    bit count outside the s_csp allocation.\n\n  - c_frotor becomes a bitmap scan start, start = c_frotor \u003e\u003e 3, and\n    then length = ((s_fpg + 7) \u003e\u003e 3) - start. A start beyond the block\n    bitmap wraps the unsigned length to a huge value, so ubh_scanc()\n    walks far past the cylinder group buffers. c_irotor drives the\n    inode bitmap the same way.\n\nA crafted image can set any of these freely, turning an ordinary\nallocation into an out of bounds access.\n\nReject a cylinder group whose recorded index does not match the group\nbeing read, or whose rotors fall outside the group, before the metadata\nis cached. Valid filesystems keep cg_cgx equal to the group number and\nthe rotors within the group, so only malformed images are rejected."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
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              "value": "AV:L - The bad cg_cgx/cg_rotor/cg_frotor/cg_irotor values come from a crafted UFS image\u0027s cylinder group block, read by ufs_read_cylinder(). They are then used by the local VFS allocate/free paths (ufs_new_fragments, ufs_free_fragments, ufs_new_inode, ufs_free_inode). No network protocol carries these bytes.\nAC:H - ufs_load_cylinder() is called only from the allocate/free paths in balloc.c and ialloc.c. These need a read-write mount, and ufs_fill_super() returns -EROFS for one unless the non-default CONFIG_UFS_FS_WRITE (\"DANGEROUS\") is set. Major distros leave it off and only a few MIPS defconfigs set it, so reaching the bug depends on a rare kernel config.\nPR:N - The attacker only has to craft the image. The ufs file_system_type sets FS_REQUIRES_DEV without FS_USERNS_MOUNT, so the mount is done by a privileged victim, not the attacker. After that, creating or extending a file triggers the allocation.\nUI:R - A victim has to mount the attacker-supplied UFS image read-write before ufs_read_cylinder() caches the malformed cylinder group fields.\nS:U - The out-of-bounds accesses stay in kernel heap memory in the same kernel security authority. No guest/host or hardware boundary is crossed.\nC:H - If c_frotor/c_irotor lie outside the group, the unsigned length in ufs_bitmap_search() wraps. ubh_scanc() then reads far past the cylinder group buffers, an unbounded out-of-bounds read of kernel memory.\nI:H - ufs_add_fragments()/ufs_free_* call fs32_add() on UFS_SB(sb)-\u003efs_cs(ucpi-\u003ec_cgx). An attacker-chosen c_cgx beyond s_ncg adds to a 32-bit value outside the s_csp heap allocation, an out-of-bounds heap write at a chosen index.\nA:H - The wild ubh_scanc() walk and the out-of-bounds fs_cs() writes can oops the kernel or corrupt the heap, crashing the system."
            }
          ]
        }
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      "providerMetadata": {
        "dateUpdated": "2026-09-25T14:41:38.420Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/5902a95066883cf96fa15b2680694fc5dd0c7d11"
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        },
        {
          "url": "https://git.kernel.org/stable/c/c9d263be26806d388129fab8c6904bed197fc6af"
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      ],
      "title": "ufs: validate cylinder group metadata before caching it",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-97926",
    "datePublished": "2026-09-25T10:22:44.197Z",
    "dateReserved": "2026-09-25T10:18:58.203Z",
    "dateUpdated": "2026-09-25T14:41:38.420Z",
    "state": "PUBLISHED"
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      "date": "2026-09-26",
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      "percentile": "0.03802"
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      "cve": {
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                "product": "Linux",
                "programFiles": [
                  "fs/ufs/cylinder.c"
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nufs: validate cylinder group metadata before caching it\n\nufs_read_cylinder() copies the cylinder group index and the rotor\npositions straight from the on-disk group and caches them without any\ncheck:\n\n\tucpi-\u003ec_cgx    = fs32_to_cpu(sb, ucg-\u003ecg_cgx);\n\tucpi-\u003ec_rotor  = fs32_to_cpu(sb, ucg-\u003ecg_rotor);\n\tucpi-\u003ec_frotor = fs32_to_cpu(sb, ucg-\u003ecg_frotor);\n\tucpi-\u003ec_irotor = fs32_to_cpu(sb, ucg-\u003ecg_irotor);\n\nThey are then used as indices during allocation and free:\n\n  - c_cgx indexes the cylinder summary array as\n    UFS_SB(sb)-\u003efs_cs(ucpi-\u003ec_cgx), so a value past s_ncg writes a 32\n    bit count outside the s_csp allocation.\n\n  - c_frotor becomes a bitmap scan start, start = c_frotor \u003e\u003e 3, and\n    then length = ((s_fpg + 7) \u003e\u003e 3) - start. A start beyond the block\n    bitmap wraps the unsigned length to a huge value, so ubh_scanc()\n    walks far past the cylinder group buffers. c_irotor drives the\n    inode bitmap the same way.\n\nA crafted image can set any of these freely, turning an ordinary\nallocation into an out of bounds access.\n\nReject a cylinder group whose recorded index does not match the group\nbeing read, or whose rotors fall outside the group, before the metadata\nis cached. Valid filesystems keep cg_cgx equal to the group number and\nthe rotors within the group, so only malformed images are rejected."
          }
        ],
        "id": "CVE-2026-97926",
        "lastModified": "2026-09-25T15:18:02.327",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.0,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "REQUIRED",
                "vectorString": "CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
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              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
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        "published": "2026-09-25T11:17:19.833",
        "references": [
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}



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