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CVE-2026-63888

Estado: Pendiente de análisisCrítica (9.8)—

In the Linux kernel, the following vulnerability has been resolved:

scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()

Two latent bugs in the Text-phase handler, both present since the original LIO integration in commit e48354ce078c ("iscsi-target: Add iSCSI fabric support for target v4.1"):

1) DataDigest CRC buffer overread (4 bytes past text_in).

Both fixes are one-liners. The Text PDU state machine is unchanged and the wire protocol is unaffected.

Detalles técnicos trazas, registros y código del informe original
   text_in is kzalloc()'d at ALIGN(payload_length, 4).  rx_size is then
   incremented by ISCSI_CRC_LEN to make room for the received DataDigest
   in the iovec, but the same (now-bumped) rx_size is passed as the
   buffer length to iscsit_crc_buf():

       if (conn->conn_ops->DataDigest) {
               ...
               rx_size += ISCSI_CRC_LEN;
       }
       ...
       if (conn->conn_ops->DataDigest) {
               data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);

   iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so
   when DataDigest is negotiated it reads 4 bytes past the end of the
   text_in allocation.  KASAN reproduces this directly on the unpatched
   mainline tree as slab-out-of-bounds in crc32c() called from the Text
   PDU path.  The OOB bytes feed crc32c() and are then compared against
   the initiator-supplied checksum, so the value does not flow back to
   the attacker, but the kernel does read past the buffer on every Text
   PDU with DataDigest=CRC32C.

   Fix by passing the actual padded payload length
   (ALIGN(payload_length, 4)) that was used for the kzalloc().

2) Stale cmd->text_in_ptr re-free (double-free) on ERL>0 bad DataDigest
   drop.

   On DataDigest mismatch with ErrorRecoveryLevel > 0 the handler
   silently drops the PDU and lets the initiator plug the CmdSN gap:

               kfree(text_in);
               return 0;

   cmd->text_in_ptr still points at the freed buffer.  The next Text
   Request on the same ITT re-enters iscsit_setup_text_cmd(), which
   unconditionally does

       kfree(cmd->text_in_ptr);
       cmd->text_in_ptr = NULL;

   freeing the same pointer a second time.  Session teardown via
   iscsit_release_cmd() has the same shape and hits the same double-free
   if the connection is dropped before a second Text Request arrives.

   On an unmodified mainline tree the bug-1 CRC overread fires first on
   the initial valid Text Request and perturbs the subsequent state, so
   #4 was isolated by building a kernel with only the bug-1 hunk of this
   patch applied plus temporary printk() observability around the three
   relevant kfree() sites.  The observability prints are not part of
   this patch.  On that build, a three-PDU Text Request sequence after
   login produces two back-to-back splats:

       BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??
       BUG: KASAN: double-free in iscsit_release_cmd+0x??

   showing the same pointer freed in the ERL>0 drop path and again in
   iscsit_setup_text_cmd() (next Text Request on the same ITT) and once
   more in iscsit_release_cmd() (session teardown).  On distro kernels
   with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free
   becomes a remote kernel BUG(); on non-hardened kernels it corrupts
   the slab freelist.

   Fix by clearing cmd->text_in_ptr after the kfree() in the ERL>0 drop
   path.  With both hunks applied #4 is directly observable on the stock
   tree without observability printks; fixing bug-1 alone would mask #4
   less, not more, so the hunks are submitted together.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad en kernel Linux accesible remotamente sin autenticación (AV:N, PR:N). Buffer overread y double-free en iSCSI target permiten DoS y corrupción de memoria de slab freelist.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network TrafficVulnerability ScanningPrivileged Account ManagementNetwork SegmentationLimit Access to Resource Over NetworkApplication Isolation and Sandboxing

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux KernelAI

Referencias

JSON original (NVD)

Mostrar
{
  "id": "CVE-2026-63888",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.8,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
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              "status": "affected",
              "version": "e48354ce078c079996f89d715dfa44814b4eba01",
              "lessThan": "f7948af0dd03de84079dcd4dc215a69fd6fbb95d",
              "versionType": "git"
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              "versionType": "git"
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              "lessThan": "6e22a1cdcc8277af4acc43710577157b77a02c5d",
              "versionType": "git"
            },
            {
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              "lessThan": "ec9f19d52074a191ed1756ed4a7d39fff1a2085c",
              "versionType": "git"
            },
            {
              "status": "affected",
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              "versionType": "git"
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            {
              "status": "affected",
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              "versionType": "git"
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              "versionType": "git"
            }
          ],
          "programFiles": [
            "drivers/target/iscsi/iscsi_target.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
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              "status": "affected",
              "version": "3.1"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "3.1",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.10.259",
              "versionType": "semver",
              "lessThanOrEqual": "5.10.*"
            },
            {
              "status": "unaffected",
              "version": "5.15.210",
              "versionType": "semver",
              "lessThanOrEqual": "5.15.*"
            },
            {
              "status": "unaffected",
              "version": "6.1.176",
              "versionType": "semver",
              "lessThanOrEqual": "6.1.*"
            },
            {
              "status": "unaffected",
              "version": "6.6.143",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.93",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.35",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver",
              "lessThanOrEqual": "7.0.*"
            },
            {
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "drivers/target/iscsi/iscsi_target.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-07-19T16:17:05.997",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/5118ea225fe63b44207ba88047e4866e1ea43812",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/6e22a1cdcc8277af4acc43710577157b77a02c5d",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/89c81d1228c00fa6dd91de6c1c5aa1ef8a7875e3",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/d3e9b79aa794f7a23e82de4d710e7d2df610e349",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/ec9f19d52074a191ed1756ed4a7d39fff1a2085c",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/f7948af0dd03de84079dcd4dc215a69fd6fbb95d",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()\n\nTwo latent bugs in the Text-phase handler, both present since the\noriginal LIO integration in commit e48354ce078c (\"iscsi-target: Add\niSCSI fabric support for target v4.1\"):\n\n1) DataDigest CRC buffer overread (4 bytes past text_in).\n\n   text_in is kzalloc()'d at ALIGN(payload_length, 4).  rx_size is then\n   incremented by ISCSI_CRC_LEN to make room for the received DataDigest\n   in the iovec, but the same (now-bumped) rx_size is passed as the\n   buffer length to iscsit_crc_buf():\n\n       if (conn->conn_ops->DataDigest) {\n               ...\n               rx_size += ISCSI_CRC_LEN;\n       }\n       ...\n       if (conn->conn_ops->DataDigest) {\n               data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);\n\n   iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so\n   when DataDigest is negotiated it reads 4 bytes past the end of the\n   text_in allocation.  KASAN reproduces this directly on the unpatched\n   mainline tree as slab-out-of-bounds in crc32c() called from the Text\n   PDU path.  The OOB bytes feed crc32c() and are then compared against\n   the initiator-supplied checksum, so the value does not flow back to\n   the attacker, but the kernel does read past the buffer on every Text\n   PDU with DataDigest=CRC32C.\n\n   Fix by passing the actual padded payload length\n   (ALIGN(payload_length, 4)) that was used for the kzalloc().\n\n2) Stale cmd->text_in_ptr re-free (double-free) on ERL>0 bad DataDigest\n   drop.\n\n   On DataDigest mismatch with ErrorRecoveryLevel > 0 the handler\n   silently drops the PDU and lets the initiator plug the CmdSN gap:\n\n               kfree(text_in);\n               return 0;\n\n   cmd->text_in_ptr still points at the freed buffer.  The next Text\n   Request on the same ITT re-enters iscsit_setup_text_cmd(), which\n   unconditionally does\n\n       kfree(cmd->text_in_ptr);\n       cmd->text_in_ptr = NULL;\n\n   freeing the same pointer a second time.  Session teardown via\n   iscsit_release_cmd() has the same shape and hits the same double-free\n   if the connection is dropped before a second Text Request arrives.\n\n   On an unmodified mainline tree the bug-1 CRC overread fires first on\n   the initial valid Text Request and perturbs the subsequent state, so\n   #4 was isolated by building a kernel with only the bug-1 hunk of this\n   patch applied plus temporary printk() observability around the three\n   relevant kfree() sites.  The observability prints are not part of\n   this patch.  On that build, a three-PDU Text Request sequence after\n   login produces two back-to-back splats:\n\n       BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??\n       BUG: KASAN: double-free in iscsit_release_cmd+0x??\n\n   showing the same pointer freed in the ERL>0 drop path and again in\n   iscsit_setup_text_cmd() (next Text Request on the same ITT) and once\n   more in iscsit_release_cmd() (session teardown).  On distro kernels\n   with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free\n   becomes a remote kernel BUG(); on non-hardened kernels it corrupts\n   the slab freelist.\n\n   Fix by clearing cmd->text_in_ptr after the kfree() in the ERL>0 drop\n   path.  With both hunks applied #4 is directly observable on the stock\n   tree without observability printks; fixing bug-1 alone would mask #4\n   less, not more, so the hunks are submitted together.\n\nBoth fixes are one-liners.  The Text PDU state machine is unchanged and\nthe wire protocol is unaffected."
    }
  ],
  "lastModified": "2026-07-27T17:44:23.777",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}