{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "range": [
                  {
                    "fixed": "a9b21fb354e8468dd15db307c3e599dc68b7ef33"
                  }
                ],
                "source": "REFERENCES_COMMIT"
              }
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "a9b21fb354e8468dd15db307c3e599dc68b7ef33"
            }
          ],
          "repo": "https://github.com/zephyrproject-rtos/zephyr",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-gm6w-pv43-m3vf"
  ],
  "database_specific": {
    "cna_assigner": "zephyr",
    "cwe_ids": [
      "CWE-362"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78118.json",
    "unresolved_ranges": [
      {
        "extracted_events": [
          {
            "range": [
              {
                "introduced": "2.2.0"
              },
              {
                "fixed": "4.5.0"
              }
            ],
            "source": "AFFECTED_FIELD",
            "strategy": "StandardRange"
          }
        ]
      }
    ]
  },
  "details": "The kernel helper z_waitq_head() (kernel/include/wait_q.h) reads the head of a thread wait queue, but on SMP systems it was called from several places without holding the scheduler spinlock _sched_spinlock that serializes wait-queue mutation. The consequential call site is z_timer_expiration_handler() in kernel/timer.c, which held only the timer subsystem lock timer_lock while reading timer-\u003ewait_q and then unpending, setting the return value of, and readying the thread it obtained. halt_thread() in kernel/sched.c removes an aborted thread from its wait queue while holding only _sched_spinlock, so the two paths are not mutually exclusive.\n\nWhen the last waiter is removed on another CPU inside that window, sys_dlist_peek_head() can return the list sentinel — a pointer into the k_timer object itself — typed as a struct k_thread * (with CONFIG_WAITQ_SCALABLE, rb_get_min() can return an arbitrary node of a tree being restructured), or it can return a pointer to a thread that has already been unpended and, for dynamically allocated threads, freed. The handler then calls unpend_thread_no_timeout(), which performs a sys_dlist_remove() through pointers read from that object, and arch_thread_return_value_set(), which writes unconditionally through the pointer.\n\nThe result is out-of-bounds and use-after-free writes in supervisor context, plus scheduler state corruption; a milder outcome is a thread that has re-pended elsewhere being woken with a success return value from an unrelated blocking call. All of the primitives needed to drive the interleaving — k_timer_start(), k_timer_status_sync(), k_thread_create() and k_thread_abort() — are system calls, so with CONFIG_USERSPACE enabled an unprivileged user-mode thread can attempt the race against kernel-owned data.\n\nExploitation requires a multi-CPU build (CONFIG_MP_MAX_NUM_CPUS greater than one; the affected region is a no-op on uniprocessor targets), local code execution, and winning a narrow timing window, so the practical outcome is most often a kernel crash rather than controlled corruption. The fix splits the helper into z_waitq_head_locked() for callers that already hold the scheduler spinlock and a z_waitq_head() that acquires it, and brings the timer expiration handler's head read, unpend and ready under a single LOCK_SCHED_SPINLOCK region.",
  "id": "CVE-2026-78118",
  "modified": "2026-10-22T02:31:00.999837146Z",
  "published": "2026-10-21T18:19:32.200Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78118.json"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/zephyrproject-rtos/zephyr"
    },
    {
      "type": "FIX",
      "url": "https://github.com/zephyrproject-rtos/zephyr/commit/a9b21fb354e8468dd15db307c3e599dc68b7ef33"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-gm6w-pv43-m3vf"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78118"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Race condition on kernel wait queues: unlocked z_waitq_head() read in the timer expiration handler can yield a stale or sentinel thread pointer on SMP"
}