CVE-2026-79976

{
  "id": "CVE-2026-79976",
  "sourceIdentifier": "[email protected]",
  "published": "2026-10-21T19:17:04.060",
  "lastModified": "2026-10-23T22:17:01.197",
  "vulnStatus": "Awaiting Analysis",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "The MCTP-over-I2C+GPIO target binding in subsys/pmci/mctp/mctp_i2c_gpio_target.c emulates a small pseudo-register file, where the bus controller first writes a register number and then writes or reads payload bytes. The selected register (b->reg_addr) and the data-phase flag (b->rxtx) were never cleared when the controller issued an I2C STOP, so after a completed transfer the target still had a data register selected while the packet buffer that register refers to had already been consumed and set to NULL by mctp_i2c_gpio_target_stop().\n\nA controller on the bus can re-enter the same branch of mctp_i2c_gpio_target_stop() with a NULL buffer using two ordinary transactions and no authentication: first a normal packet write to MCTP_I2C_GPIO_RX_MSG_ADDR followed by STOP (which delivers and frees b->rx_pkt), then a bare read transaction followed by STOP. The failing read_requested() call leaves the stale state untouched and the I2C driver still delivers the STOP callback, which then calls mctp_bus_rx() with a NULL packet. The symmetric case exists on the transmit side, where the stale MCTP_I2C_GPIO_TX_MSG_ADDR selection dereferences b->tx_pkt->end after b->tx_pkt has been cleared and additionally signals b->tx_complete a second time, causing the next outbound packet to be dropped.\n\nThe dereference happens in the I2C target interrupt handler, so on any target that traps accesses to address 0 the result is a fatal exception and a device reset or halt — a denial of service inflicted by any device able to act as controller on the shared management bus (for example compromised firmware on a peer MCTP endpoint or on the BMC). On parts where address 0 is readable, the impact degrades to a malformed packet buffer being handed to the MCTP stack and lost transmit packets. No attacker-controlled value is written and no confidentiality or integrity boundary is crossed.\n\nThe fix resets b->reg_addr to MCTP_I2C_GPIO_INVALID_ADDR and clears b->rxtx at every STOP, so a new register must be selected before any data phase can run again. Only builds that opt into the experimental CONFIG_MCTP subsystem with CONFIG_MCTP_I2C_GPIO_TARGET=y are affected."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "zephyrproject",
          "product": "zephyr",
          "defaultStatus": "unaffected",
          "collectionURL": "https://github.com/zephyrproject-rtos/zephyr",
          "packageName": "zephyr",
          "programFiles": [
            "subsys/pmci/mctp/mctp_i2c_gpio_target.c"
          ],
          "programRoutines": [
            {
              "name": "mctp_i2c_gpio_target_read_processed"
            },
            {
              "name": "mctp_i2c_gpio_target_read_requested"
            },
            {
              "name": "mctp_i2c_gpio_target_stop"
            }
          ],
          "versions": [
            {
              "version": "4.3.0",
              "lessThanOrEqual": "4.4.2",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H",
          "baseScore": 7.1,
          "baseSeverity": "HIGH",
          "attackVector": "ADJACENT_NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "LOW",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 4.2
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-10-23T20:43:08.859407Z",
          "id": "CVE-2026-79976",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-476"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://github.com/zephyrproject-rtos/zephyr/commit/60f7fee438504de29f2473d7a8d0535235b983ef",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq",
      "source": "[email protected]"
    }
  ]
}