{"id":"CVE-2026-79976","summary":"NULL pointer dereference in the MCTP I2C+GPIO target binding triggerable by a peer I2C controller","details":"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-\u003ereg_addr) and the data-phase flag (b-\u003erxtx) 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-\u003erx_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-\u003etx_pkt-\u003eend after b-\u003etx_pkt has been cleared and additionally signals b-\u003etx_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-\u003ereg_addr to MCTP_I2C_GPIO_INVALID_ADDR and clears b-\u003erxtx 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.","aliases":["GHSA-76fx-m4mf-24gq"],"modified":"2026-10-22T07:31:34.326386595Z","published":"2026-10-21T18:19:34.519Z","database_specific":{"cna_assigner":"zephyr","cwe_ids":["CWE-476"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/79xxx/CVE-2026-79976.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/79xxx/CVE-2026-79976.json"},{"type":"PACKAGE","url":"https://github.com/zephyrproject-rtos/zephyr"},{"type":"FIX","url":"https://github.com/zephyrproject-rtos/zephyr/commit/60f7fee438504de29f2473d7a8d0535235b983ef"},{"type":"ADVISORY","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-79976"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/zephyrproject-rtos/zephyr","events":[{"introduced":"3568e1b6d5cdd51a6b964a2a1d6d29200fea2056"},{"last_affected":"dccb09599635bdff17633fa7e9dab014b91dce90"},{"fixed":"60f7fee438504de29f2473d7a8d0535235b983ef"}],"database_specific":{"extracted_events":[{"range":[{"introduced":"4.3.0"},{"last_affected":"4.4.2"}],"source":"AFFECTED_FIELD","strategy":"StandardRange"},{"range":[{"fixed":"60f7fee438504de29f2473d7a8d0535235b983ef"}],"source":"REFERENCES_COMMIT"}]}}],"versions":["v4.4.2","v4.4.2-rc1","v4.4.1","v4.4.1-rc1","v4.4.0","v4.4.0-rc3","v4.4.0-rc2","v4.4.0-rc1","v4.3.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-79976.json","vanir_signatures":[{"id":"CVE-2026-79976-50a5ec9e","signature_type":"Function","signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/60f7fee438504de29f2473d7a8d0535235b983ef","target":{"function":"mctp_i2c_gpio_target_stop","file":"subsys/pmci/mctp/mctp_i2c_gpio_target.c"},"deprecated":false,"digest":{"length":856,"function_hash":"176893827543129801811059062069228627721"}},{"signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/60f7fee438504de29f2473d7a8d0535235b983ef","target":{"file":"subsys/pmci/mctp/mctp_i2c_gpio_target.c"},"deprecated":false,"digest":{"threshold":0.9,"line_hashes":["220874209762409506206246963739310088927","267868390585593816517915983992887850017","105129646669878179696673523646555507170"]},"id":"CVE-2026-79976-daff5acc","signature_type":"Line"}],"vanir_signatures_modified":"2026-10-22T07:31:34Z"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H"}]}