CVE-2026-63888 (GCVE-0-2026-63888)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-07-20 13:41
VLAI
Title
scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()
Summary
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). 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. Both fixes are one-liners. The Text PDU state machine is unchanged and the wire protocol is unaffected.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < f7948af0dd03de84079dcd4dc215a69fd6fbb95d (git)
Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < badf178b76b0690851df00f4ca9cf2eb8eb0f963 (git)
Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < 6e22a1cdcc8277af4acc43710577157b77a02c5d (git)
Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < d3e9b79aa794f7a23e82de4d710e7d2df610e349 (git)
Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < ec9f19d52074a191ed1756ed4a7d39fff1a2085c (git)
Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < 89c81d1228c00fa6dd91de6c1c5aa1ef8a7875e3 (git)
Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < 5118ea225fe63b44207ba88047e4866e1ea43812 (git)
Affected: e48354ce078c079996f89d715dfa44814b4eba01 , < 778c2ab142c625a8a8afa570e0f9b7873f445d99 (git)
Create a notification for this product.
Linux Linux Affected: 3.1
Unaffected: 0 , < 3.1 (semver)
Unaffected: 5.10.259 , ≤ 5.10.* (semver)
Unaffected: 5.15.210 , ≤ 5.15.* (semver)
Unaffected: 6.1.176 , ≤ 6.1.* (semver)
Unaffected: 6.6.143 , ≤ 6.6.* (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
Create a notification for this product.
Show details on NVD website
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      "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()\u0027d 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-\u003econn_ops-\u003eDataDigest) {\n               ...\n               rx_size += ISCSI_CRC_LEN;\n       }\n       ...\n       if (conn-\u003econn_ops-\u003eDataDigest) {\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-\u003etext_in_ptr re-free (double-free) on ERL\u003e0 bad DataDigest\n   drop.\n\n   On DataDigest mismatch with ErrorRecoveryLevel \u003e 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-\u003etext_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-\u003etext_in_ptr);\n       cmd-\u003etext_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\u003e0 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-\u003etext_in_ptr after the kfree() in the ERL\u003e0 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."
        }
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            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
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        "dateUpdated": "2026-07-20T13:41:14.224Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f7948af0dd03de84079dcd4dc215a69fd6fbb95d"
        },
        {
          "url": "https://git.kernel.org/stable/c/badf178b76b0690851df00f4ca9cf2eb8eb0f963"
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        {
          "url": "https://git.kernel.org/stable/c/6e22a1cdcc8277af4acc43710577157b77a02c5d"
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        {
          "url": "https://git.kernel.org/stable/c/d3e9b79aa794f7a23e82de4d710e7d2df610e349"
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          "url": "https://git.kernel.org/stable/c/ec9f19d52074a191ed1756ed4a7d39fff1a2085c"
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        },
        {
          "url": "https://git.kernel.org/stable/c/778c2ab142c625a8a8afa570e0f9b7873f445d99"
        }
      ],
      "title": "scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63888",
    "datePublished": "2026-07-19T14:55:00.803Z",
    "dateReserved": "2026-07-19T07:54:57.018Z",
    "dateUpdated": "2026-07-20T13:41:14.224Z",
    "state": "PUBLISHED"
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    "epss": {
      "cve": "CVE-2026-63888",
      "date": "2026-07-21",
      "epss": "0.00755",
      "percentile": "0.51076"
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    "nvd": "{\"cve\":{\"id\":\"CVE-2026-63888\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-07-19T16:17:05.997\",\"lastModified\":\"2026-07-20T15:16:54.243\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"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()\u0027d 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-\u003econn_ops-\u003eDataDigest) {\\n               ...\\n               rx_size += ISCSI_CRC_LEN;\\n       }\\n       ...\\n       if (conn-\u003econn_ops-\u003eDataDigest) {\\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-\u003etext_in_ptr re-free (double-free) on ERL\u003e0 bad DataDigest\\n   drop.\\n\\n   On DataDigest mismatch with ErrorRecoveryLevel \u003e 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-\u003etext_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-\u003etext_in_ptr);\\n       cmd-\u003etext_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\u003e0 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-\u003etext_in_ptr after the kfree() in the ERL\u003e0 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.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"drivers/target/iscsi/iscsi_target.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"f7948af0dd03de84079dcd4dc215a69fd6fbb95d\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"badf178b76b0690851df00f4ca9cf2eb8eb0f963\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"6e22a1cdcc8277af4acc43710577157b77a02c5d\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"d3e9b79aa794f7a23e82de4d710e7d2df610e349\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"ec9f19d52074a191ed1756ed4a7d39fff1a2085c\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"89c81d1228c00fa6dd91de6c1c5aa1ef8a7875e3\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"5118ea225fe63b44207ba88047e4866e1ea43812\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"e48354ce078c079996f89d715dfa44814b4eba01\",\"lessThan\":\"778c2ab142c625a8a8afa570e0f9b7873f445d99\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"drivers/target/iscsi/iscsi_target.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"3.1\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"3.1\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.259\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.210\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.176\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.143\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.93\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.35\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.0.12\",\"lessThanOrEqual\":\"7.0.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}]},\"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\"},{\"url\":\"https://git.kernel.org/stable/c/778c2ab142c625a8a8afa570e0f9b7873f445d99\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/89c81d1228c00fa6dd91de6c1c5aa1ef8a7875e3\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/badf178b76b0690851df00f4ca9cf2eb8eb0f963\",\"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\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-07-21T14:56:25+00:00",
      "cve": "CVE-2026-63888",
      "id": "CVE-2026-63888",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_affected": "260",
      "product_status:known_not_affected": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63888.json",
      "version": "3"
    }
  }
}



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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.


Detection rules are retrieved from Rulezet.