CVE-2026-89720 (GCVE-0-2026-89720)
Vulnerability from cvelistv5
Published
2026-09-11 19:46
Modified
2026-10-19 08:51
Severity ?
7.7 (High) - CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ubifs: fix out-of-bounds read in signature length check ubifs_sb_verify_signature() bounds the on-disk ubifs_sig_node->len field before handing the signature payload to verify_pkcs7_signature(), but the check has the wrong sign: if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node)) The signature bytes start sizeof(struct ubifs_sig_node) (UBIFS_SIG_NODE_SZ, 64 bytes) into the node, so the payload is at most snod->len - sizeof(struct ubifs_sig_node) bytes long. Adding the header size instead of subtracting it accepts a declared length up to 2 * UBIFS_SIG_NODE_SZ larger than the node actually holds -- past the end of c->sbuf, which is vmalloc(c->leb_size). verify_pkcs7_signature() -> pkcs7_parse_message() -> asn1_ber_decoder() is then handed that inflated length and reads beyond the allocation while walking the DER headers. The node length comes straight from the mounted image, so a crafted signed UBIFS image reaches this via ubifs_read_superblock() before the signature is cryptographically checked. snod->len is guaranteed to be >= UBIFS_SIG_NODE_SZ by the node scanner (c->ranges[UBIFS_SIG_NODE].min_len == UBIFS_SIG_NODE_SZ), so the corrected subtraction cannot underflow. Legitimately signed images are unaffected: a correct superblock never declares a signature longer than the node it is embedded in.
References
Impacted products
Vendor Product Version
Linux Linux Version: 817aa094842dfc3a6b98c9582d4a647827f66201
Version: 817aa094842dfc3a6b98c9582d4a647827f66201
Version: 817aa094842dfc3a6b98c9582d4a647827f66201
Version: 817aa094842dfc3a6b98c9582d4a647827f66201
Version: 817aa094842dfc3a6b98c9582d4a647827f66201
Version: 817aa094842dfc3a6b98c9582d4a647827f66201
Version: 817aa094842dfc3a6b98c9582d4a647827f66201
Version: 817aa094842dfc3a6b98c9582d4a647827f66201
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ubifs/auth.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/ubifs/auth.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.3"
            },
            {
              "lessThan": "5.3",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.270",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.221",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.188",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.109",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.50",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.270",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.221",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.188",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.157",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.50",
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                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
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                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nubifs: fix out-of-bounds read in signature length check\n\nubifs_sb_verify_signature() bounds the on-disk ubifs_sig_node-\u003elen field\nbefore handing the signature payload to verify_pkcs7_signature(), but the\ncheck has the wrong sign:\n\n\tif (le32_to_cpu(signode-\u003elen) \u003e snod-\u003elen + sizeof(struct ubifs_sig_node))\n\nThe signature bytes start sizeof(struct ubifs_sig_node) (UBIFS_SIG_NODE_SZ,\n64 bytes) into the node, so the payload is at most\n\n\tsnod-\u003elen - sizeof(struct ubifs_sig_node)\n\nbytes long. Adding the header size instead of subtracting it accepts a\ndeclared length up to 2 * UBIFS_SIG_NODE_SZ larger than the node actually\nholds -- past the end of c-\u003esbuf, which is vmalloc(c-\u003eleb_size).\nverify_pkcs7_signature() -\u003e pkcs7_parse_message() -\u003e asn1_ber_decoder()\nis then handed that inflated length and reads beyond the allocation while\nwalking the DER headers. The node length comes straight from the mounted\nimage, so a crafted signed UBIFS image reaches this via\nubifs_read_superblock() before the signature is cryptographically checked.\n\nsnod-\u003elen is guaranteed to be \u003e= UBIFS_SIG_NODE_SZ by the node scanner\n(c-\u003eranges[UBIFS_SIG_NODE].min_len == UBIFS_SIG_NODE_SZ), so the corrected\nsubtraction cannot underflow. Legitimately signed images are unaffected: a\ncorrect superblock never declares a signature longer than the node it is\nembedded in."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.7,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The OOB read is reached only while mounting a local UBIFS/UBI volume (mount \u2192 ubifs_fill_super \u2192 mount_ubifs \u2192 ubifs_read_superblock \u2192 authenticate_sb_node \u2192 ubifs_sb_verify_signature). The inflated ubifs_sig_node-\u003elen comes from on-disk flash, not ksmbd, nfsd, or any received-packet path.\nAC:L - The attacker fully controls the on-disk SIG node size and signode-\u003elen. The inverted check accepts a payload up to snod-\u003elen+64; with a node filling the LEB that deterministically reads 128 bytes past vmalloc\u0027d c-\u003esbuf in asn1_ber_decoder(), with no race or uncontrolled layout.\nPR:N - Supplying the crafted authenticated image needs no account on the victim. ubifs_fs_type lacks FS_USERNS_MOUNT, so the CAP_SYS_ADMIN mount (boot-time auth_key mount on embedded, automotive, and IoT devices that use offline-signed UBIFS) is performed by the platform, matching the malicious-filesystem model.\nUI:N - Offline-signed UBIFS is verified automatically at mount; boot/fstab auto-mount with auth_key runs ubifs_sb_verify_signature in ubifs_read_superblock before any file access, so planting or presenting the crafted volume is sufficient with no separate victim click or open.\nS:U - The out-of-bounds read and any oops remain inside the mounting host kernel. This is a same-authority memory-safety issue, not a VM escape, IOMMU bypass, or other cross-boundary impact.\nC:H - verify_pkcs7_signature() \u2192 pkcs7_parse_message() \u2192 asn1_ber_decoder() walks an attacker-inflated length of up to 128 bytes past c-\u003esbuf (vmalloc of the LEB). That is an out-of-bounds kernel read of adjacent vmalloc memory, which is Confidentiality High rather than a few-byte leak.\nI:N - The defect is an out-of-bounds read of PKCS#7/ASN.1 headers; the decoder copies those bytes only into newly allocated parse objects sized from the claimed length and does not write past any allocation or provide an arbitrary-write or control-flow primitive.\nA:H - Reading past the vmalloc LEB buffer into an unmapped vmalloc guard page oopses or panics the kernel during mount, and a crafted image can retrigger that crash on every boot or mount of the volume."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:51:33.033Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/ab7405bd86331cc2dbc8201699d4adc33bea75e7"
        },
        {
          "url": "https://git.kernel.org/stable/c/11abc34698cb3172badf8aa12e623f1bac98bbd8"
        },
        {
          "url": "https://git.kernel.org/stable/c/8cc3da72cf57acb4b77442ea8cec48425dff7c06"
        },
        {
          "url": "https://git.kernel.org/stable/c/37a9d25a563f5f9103282954ce573c4a61321e7c"
        },
        {
          "url": "https://git.kernel.org/stable/c/f76b79d6e42af20682495bccd22f72c7164b0018"
        },
        {
          "url": "https://git.kernel.org/stable/c/a1dc246f98bb94233effa4fa3ec7bf84700bb7d1"
        },
        {
          "url": "https://git.kernel.org/stable/c/83e1aa9f5f906c9b1f4949d0521f0f950a159d96"
        },
        {
          "url": "https://git.kernel.org/stable/c/95d27c1708bb6e8823c8e7c623f9abc2a91bf4bf"
        }
      ],
      "title": "ubifs: fix out-of-bounds read in signature length check",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89720",
    "datePublished": "2026-09-11T19:46:32.923Z",
    "dateReserved": "2026-09-11T19:38:34.752Z",
    "dateUpdated": "2026-10-19T08:51:33.033Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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