CVE-2026-63996 (GCVE-0-2026-63996)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:56 – Updated: 2026-08-05 12:38
VLAI
Title
ethtool: cmis: require exact CDB reply length
Summary
In the Linux kernel, the following vulnerability has been resolved: ethtool: cmis: require exact CDB reply length Malicious SFP module could respond with rpl_len longer than what cmis_cdb_process_reply() expected, leading to OOB writes. Malicious HW is a bit theoretical but some modules may just be buggy and/or the reads may occasionally get corrupted, so let's protect the kernel. The existing check protects from short replies. We need to protect from long ones, too. All callers that pass a non-zero rpl_exp_len cast the reply payload to a fixed-layout struct and read fields at fixed offsets, with no version negotiation or short-reply handling: - cmis_cdb_validate_password() - cmis_cdb_module_features_get() - cmis_fw_update_fw_mng_features_get() so let's assume that responses longer than expected do not have to be handled gracefully here. Add a warning message to make the debug easier in case my understanding is wrong... Note that page_data->length (argument of kmalloc) comes from last arg to ethtool_cmis_page_init() which is rpl_exp_len. Note2 that AIs also like to point out overflows in args->req.payload itself (which is a fixed-size 120 B buffer, on the stack), but callers should be reading structs defined by the standard, so protecting from requests for more data than max seem like defensive programming.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: a39c84d796254e6b1662ca0c46dbc313379e9291 , < 2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3 (git)
Affected: a39c84d796254e6b1662ca0c46dbc313379e9291 , < 4d42fb88ec61f2e98c33a9e3a2de371d5edbc6b1 (git)
Affected: a39c84d796254e6b1662ca0c46dbc313379e9291 , < eb5dcd740cd7fa27bc2caeff2d28ef28e93ff4d3 (git)
Affected: a39c84d796254e6b1662ca0c46dbc313379e9291 , < 6c3f999a9d1338c6c89a9ff4549eafe72bc2e7b1 (git)
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Linux Linux Affected: 6.11
Unaffected: 0 , < 6.11 (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.
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{
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ethtool/cmis_cdb.c"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nethtool: cmis: require exact CDB reply length\n\nMalicious SFP module could respond with rpl_len longer than\nwhat cmis_cdb_process_reply() expected, leading to OOB writes.\nMalicious HW is a bit theoretical but some modules may just\nbe buggy and/or the reads may occasionally get corrupted,\nso let\u0027s protect the kernel.\n\nThe existing check protects from short replies. We need to\nprotect from long ones, too. All callers that pass a non-zero\nrpl_exp_len cast the reply payload to a fixed-layout struct\nand read fields at fixed offsets, with no version negotiation\nor short-reply handling:\n\n  - cmis_cdb_validate_password()\n  - cmis_cdb_module_features_get()\n  - cmis_fw_update_fw_mng_features_get()\n\nso let\u0027s assume that responses longer than expected do not\nhave to be handled gracefully here. Add a warning message\nto make the debug easier in case my understanding is wrong...\n\nNote that page_data-\u003elength (argument of kmalloc) comes from\nlast arg to ethtool_cmis_page_init() which is rpl_exp_len.\n\nNote2 that AIs also like to point out overflows in args-\u003ereq.payload\nitself (which is a fixed-size 120 B buffer, on the stack),\nbut callers should be reading structs defined by the standard,\nso protecting from requests for more data than max seem like\ndefensive programming."
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            "version": "3.1"
          },
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              "lang": "en",
              "value": "AV:L - The vulnerable code is reached only via the local ethtool genetlink firmware-flash path (ETHTOOL_MSG_MODULE_FW_FLASH_ACT), not from remote network input; a malicious transceiver supplies the malformed CDB reply once that local ioctl-like operation is invoked.\nAC:L - A malicious CMIS module can reliably set rpl_len up to 255 on CDB replies; no race or uncontrollable memory layout is required, and an attacker with CAP_NET_ADMIN can bring the netdev down and initiate flashing deterministically.\nPR:L - Triggering module firmware flash requires CAP_NET_ADMIN, which is enforced via GENL_UNS_ADMIN_PERM/netlink_ns_capable and is obtainable by unprivileged users inside a user namespace (unshare -Urn), not only by init-namespace root.\nUI:N - Exploitation does not require a separate victim user action beyond the attacker (or compromised local process with CAP_NET_ADMIN) issuing the ethtool module firmware-flash command; no interactive victim steps are needed.\nS:U - Impact is kernel stack corruption and potential privilege escalation or denial of service within the same kernel security boundary; this is not a VM escape, sandbox escape, or cross-authority boundary crossing.\nC:H - The out-of-bounds stack write corrupts adjacent kernel stack memory and can be leveraged for arbitrary kernel memory disclosure; related CMIS ethtool bugs in the same path have already caused demonstrable stack corruption.\nI:H - memcpy() can write up to 135 bytes past the 120-byte payload buffer on the kernel stack, enabling control-data corruption and potential arbitrary kernel code execution, not merely a bounded modification.\nA:H - Stack corruption in this CMIS firmware-flash workqueue path can trigger kernel oops/panic (as seen in the related CVE-2025-37791 stack-protector failure in the same call chain) or hang the affected system."
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        "dateUpdated": "2026-08-05T12:38:00.530Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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    "cveId": "CVE-2026-63996",
    "datePublished": "2026-07-19T14:56:15.256Z",
    "dateReserved": "2026-07-19T07:54:57.026Z",
    "dateUpdated": "2026-08-05T12:38:00.530Z",
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-07-22T00:00:31+00:00",
      "cve": "CVE-2026-63996",
      "id": "CVE-2026-63996",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_affected": "184",
      "product_status:known_not_affected": "90",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ethtool: cmis: require exact CDB reply length",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63996.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-08-06T01:10:37Z",
      "cve": "CVE-2026-63996",
      "id": "CVE-2026-63996",
      "initial_release_date": "2026-07-21T13:01:55Z",
      "product_status:known_affected": "84",
      "product_status:known_not_affected": "212",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-63996",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63996.json",
      "version": "4"
    }
  }
}



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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

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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.