# CVE-2026-19669: Unbounded variable-length array in fuel gauge syscall verifiers allows kernel stack overflow from user mode > Attacker with user-mode access can trigger kernel stack overflow via unvalidated variable-length arrays in fuel gauge syscalls, leading to code execution or crash. - **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** No - **Published:** 11 Oct 2026 - **Updated:** 15 Oct 2026 - **Also known as:** GHSA-6ghg-cmrw-8gw5 ## What is CVE-2026-19669? CVE-2026-19669 is a high-severity memory corruption vulnerability in zephyrproject zephyr, published on 11 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description The user-mode syscall verifiers z_vrfy_fuel_gauge_get_props() and z_vrfy_fuel_gauge_set_props() in drivers/fuel_gauge/fuel_gauge_syscall_handlers.c declared two variable-length arrays, union fuel_gauge_prop_val k_vals[len] and fuel_gauge_prop_t k_props[len], sized directly by the caller-supplied len argument. len is an unvalidated size_t taken straight from the syscall ABI, and the VLAs were allocated before any check at all — including before the K_SYSCALL_DRIVER_FUEL_GAUGE() object-permission check. The subsequent k_usermode_from_copy() calls validated only that the user source buffer was readable; the kernel destination was never bounds-checked, since it was sized by the same attacker-chosen len. Any thread running in user mode with CONFIG_USERSPACE enabled can invoke fuel_gauge_get_props() or fuel_gauge_set_props() with a large len. This first displaces the supervisor stack pointer by an arbitrary attacker-chosen amount — Zephyr does not build with stack-clash probing, so the displacement itself does not fault, and the nested calls made by the verifier then write frames below the privileged stack. If the caller has been granted access to a fuel-gauge device object, the memcpy inside k_usermode_from_copy() additionally writes len * sizeof(union fuel_gauge_prop_val) bytes of fully attacker-controlled data starting well below the stack base. CONFIG_PRIVILEGED_STACK_SIZE defaults to 1024 bytes, so a len of roughly 170 already exhausts it. The result is an out-of-bounds write in supervisor mode with attacker-controlled length and, on the permitted path, attacker-controlled content — a break out of the user-mode sandbox into kernel memory, leading to kernel code execution or a system crash. A stack guard region does not contain it, because the copy begins below the guard and walks upward, corrupting unprotected memory before the guard is reached. The fix removes the kernel-side copies entirely and validates the caller's arrays in place with K_SYSCALL_MEMORY_ARRAY_READ() / K_SYSCALL_MEMORY_ARRAY_WRITE(), which also handle the len * size multiplication overflow; this is safe because neither fuel_gauge_prop_t nor union fuel_gauge_prop_val contains embedded pointers. Weakness: CWE-787 (Out-of-bounds Write) ## Which versions are affected by CVE-2026-19669? ## How do I fix CVE-2026-19669? No fix has been published for CVE-2026-19669 yet. Limit exposure of the affected software until one is available. ## Is CVE-2026-19669 being exploited? There is no known exploitation of CVE-2026-19669 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-19669 and fix it if it is affected. What it is: CVE-2026-19669 is a high-severity memory corruption vulnerability in zephyrproject zephyr, published on 11 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-19669 in the wild and no public exploit code. Affected product: zephyrproject zephyr. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-19669/ (Markdown: https://insights.sbomify.com/CVE-2026-19669/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19669 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19669 - OSV: https://osv.dev/vulnerability/CVE-2026-19669 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-19669/ Summaries are generated and may contain mistakes; the official description above is the record.