{"id":"CVE-2026-79976","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-79976","generatedAt":"2026-10-28T03:32:14.681Z","title":"The 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…","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.","published":"2026-10-21T19:17:04.000Z","lastModified":"2026-10-23T22:17:01.000Z","status":"Awaiting Analysis","sourceIdentifier":"vulnerabilities@zephyrproject.org","cvss":{"version":"3.1","score":7.1,"severity":"HIGH","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H"},"cwe":["CWE-476"],"affected":[],"epss":{"score":0.00256,"percentile":0.17131,"date":"2026-10-27","history":[{"date":"2026-10-22","score":0.00207,"percentile":0.10207}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.26%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"new","label":"New CVE","at":"2026-10-21T19:17:04.000Z","detail":{"score":"7.1","severity":"HIGH","publishedAt":"2026-10-21T19:17:04.060Z"},"summary":"New CVE, high severity (CVSS 7.1)."}],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/60f7fee438504de29f2473d7a8d0535235b983ef","source":"vulnerabilities@zephyrproject.org"},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-76fx-m4mf-24gq","source":"vulnerabilities@zephyrproject.org"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-79976","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}