{"id":"CVE-2026-79976","revision":null,"records":[{"revision":"7c5a08f5f6e44146a002f7a0278f0400","observedAt":"2026-10-23T22:48:20.692+00:00","statement":{"source":"cve-program","id":"CVE-2026-79976","aliases":[],"title":"NULL pointer dereference in the MCTP I2C+GPIO target binding triggerable by a peer I2C controller","description":"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.","state":0,"publishedAt":"2026-10-21T18:19:34.519+00:00","modifiedAt":"2026-10-23T21:27:29.128+00:00","affected":[{"ecosystem":"https://github.com/zephyrproject-rtos/zephyr","name":"zephyr","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"zephyrproject\",\n                    \"product\": \"zephyr\",\n                    \"collectionURL\": \"https://github.com/zephyrproject-rtos/zephyr\",\n                    \"packageName\": \"zephyr\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"programFiles\": [\n                        \"subsys/pmci/mctp/mctp_i2c_gpio_target.c\"\n                    ],\n                    \"programRoutines\": [\n                        {\n                            \"name\": \"mctp_i2c_gpio_target_read_processed\"\n                        },\n                        {\n                            \"name\": \"mctp_i2c_gpio_target_read_requested\"\n                        },\n                        {\n                            \"name\": \"mctp_i2c_gpio_target_stop\"\n                        }\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"4.3.0\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"semver\",\n                            \"lessThanOrEqual\": \"4.4.2\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H","score":7.1,"severity":"HIGH"}],"references":["https://github.com/zephyrproject-rtos/zephyr/commit/60f7fee438504de29f2473d7a8d0535235b983ef","https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-79976","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-79976","identifiers":["CVE-2026-79976"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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