# CVE-2025-40009: fs/proc/task_mmu: check p->vec_buf for NULL > A local attacker can trigger a kernel panic via a specific ioctl call, causing a denial of service. - **Severity:** Not scored - **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:** Yes - **Published:** 20 Oct 2025 - **Updated:** 11 May 2026 - **Also known as:** BELL-CVE-2025-40009, DEBIAN-CVE-2025-40009, GHSA-cmvf-g3gj-cgc9, ROOT-OS-DEBIAN-13-CVE-2025-40009, ROOT-OS-UBUNTU-2404-CVE-2025-40009, UBUNTU-CVE-2025-40009 ## What is CVE-2025-40009? CVE-2025-40009 is a vulnerability in Linux, published on 20 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description In the Linux kernel, the following vulnerability has been resolved: fs/proc/task_mmu: check p->vec_buf for NULL When the PAGEMAP_SCAN ioctl is invoked with vec_len = 0 reaches pagemap_scan_backout_range(), kernel panics with null-ptr-deref: [ 44.936808] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 44.937797] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] [ 44.938391] CPU: 1 UID: 0 PID: 2480 Comm: reproducer Not tainted 6.17.0-rc6 #22 PREEMPT(none) [ 44.939062] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 44.939935] RIP: 0010:pagemap_scan_thp_entry.isra.0+0x741/0xa80 [ 44.946828] Call Trace: [ 44.947030] [ 44.949219] pagemap_scan_pmd_entry+0xec/0xfa0 [ 44.952593] walk_pmd_range.isra.0+0x302/0x910 [ 44.954069] walk_pud_range.isra.0+0x419/0x790 [ 44.954427] walk_p4d_range+0x41e/0x620 [ 44.954743] walk_pgd_range+0x31e/0x630 [ 44.955057] __walk_page_range+0x160/0x670 [ 44.956883] walk_page_range_mm+0x408/0x980 [ 44.958677] walk_page_range+0x66/0x90 [ 44.958984] do_pagemap_scan+0x28d/0x9c0 [ 44.961833] do_pagemap_cmd+0x59/0x80 [ 44.962484] __x64_sys_ioctl+0x18d/0x210 [ 44.962804] do_syscall_64+0x5b/0x290 [ 44.963111] entry_SYSCALL_64_after_hwframe+0x76/0x7e vec_len = 0 in pagemap_scan_init_bounce_buffer() means no buffers are allocated and p->vec_buf remains set to NULL. This breaks an assumption made later in pagemap_scan_backout_range(), that page_region is always allocated for p->vec_buf_index. Fix it by explicitly checking p->vec_buf for NULL before dereferencing. Other sites that might run into same deref-issue are already (directly or transitively) protected by checking p->vec_buf. Note: From PAGEMAP_SCAN man page, it seems vec_len = 0 is valid when no output is requested and it's only the side effects caller is interested in, hence it passes check in pagemap_scan_get_args(). This issue was found by syzkaller. ## Which versions are affected by CVE-2025-40009? ## How do I fix CVE-2025-40009? Apply the vendor's patch. ## Is CVE-2025-40009 being exploited? There is no known exploitation of CVE-2025-40009 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2025-40009 and fix it if it is affected. What it is: CVE-2025-40009 is a vulnerability in Linux, published on 20 Oct 2025. 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-2025-40009 in the wild and no public exploit code. Affected product: Linux. 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-2025-40009/ (Markdown: https://insights.sbomify.com/CVE-2025-40009/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40009 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40009 - OSV: https://osv.dev/vulnerability/CVE-2025-40009 --- From sbomify Insights: https://insights.sbomify.com/CVE-2025-40009/ Summaries are generated and may contain mistakes; the official description above is the record.