{"schema":"threatline.record/2","record":{"id":"CVE-2026-79976","aliases":["GHSA-76fx-m4mf-24gq"],"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->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.","categories":["Unclassified"],"product":"zephyr","vendor":"zephyrproject","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-79976","source_modified_at":"2026-10-23T21:27:29.128Z","fetched_at":"2026-10-23T21:47:51.402276Z","product":"zephyr","vendor":"zephyrproject","versions":[{"version":"4.3.0","status":"affected","versionType":"semver","lessThanOrEqual":"4.4.2"}],"defaultStatus":"unaffected"},{"source":"GitHub Advisory Database","source_url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq","source_modified_at":"2026-10-21T18:07:51Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"other","name":"zephyr"},"range":">= 4.3.0, <= 4.4.2"}],"fixed_versions":[{"source":"GitHub Advisory Database","source_url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq","source_modified_at":"2026-10-21T18:07:51Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"other","name":"zephyr"},"version":"4.5.0"}],"cvss":7.1,"severity":"High","kev":{"listed":false},"epss":{"probability":0.00207,"percentile":0.10209,"score_date":"2026-10-23"},"published_at":"2026-10-21T18:19:34.519Z","modified_at":"2026-10-23T21:27:29.128Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-79976","fetched_at":"2026-10-23T21:47:51.402276Z","source_modified_at":"2026-10-23T21:27:29.128Z"},{"source":"GitHub Advisory Database","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-21T18:07:51Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-79976","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","GitHub Advisory Database","EPSS"],"references":[{"source":"CVE List","url":"https://github.com/zephyrproject-rtos/zephyr/commit/60f7fee438504de29f2473d7a8d0535235b983ef","tags":["patch"]},{"source":"CVE List","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","cvss_source":"CVE List","ssvc":{"exploitation":"none","automatable":"no","technical_impact":"partial","assessed_at":"2026-10-23T20:43:08.859407Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":null,"confidence":"unknown","reviewed":false},"change_timestamp":"2026-10-23T21:27:29.128Z","content_hash":"da907d223327844b90ce8a46db4606e545f8d75a88d199aaba29e997b27c8603"}}