From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2025-40364][LOW] io_uring: fix io_req_prep_async with provided buffers io_req_prep_async() can import provided buffers, commit the ring state by giving up on that before, it'll be reimported later if needed. Reported-by: Muhammad Ramdhan Reported-by: Bing-Jhong Billy Jheng Reported-by: Jacob Soo Fixes: c7fb194 ("io_uring: add support for ring mapped supplied buffers") Signed-off-by: Pavel Begunkov Signed-off-by: Greg Kroah-Hartman Date: Thu, 24 Sep 2026 17:24:13 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2025-40364 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: a1b17713b32c75a90132ea2f92b1257f3bbc20f3 List-Id: CVE: CVE-2025-40364 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: io_uring: fix io_req_prep_async with provided buffers io_req_prep_async() can import provided buffers, commit the ring state by giving up on that before, it'll be reimported later if needed. Reported-by: Muhammad Ramdhan Reported-by: Bing-Jhong Billy Jheng Reported-by: Jacob Soo Fixes: c7fb194 ("io_uring: add support for ring mapped supplied buffers") Signed-off-by: Pavel Begunkov Signed-off-by: Greg Kroah-Hartman Commit: a1b17713b32c75a90132ea2f92b1257f3bbc20f3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a1b17713b32c75a90132ea2f92b1257f3bbc20f3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-40364 Analysis date: Thu, 24 Sep 2026 17:24:13 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2025-40364 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-40364 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2025-40364 LOW https://www.kernelcve.org/list/?q=CVE-2025-40364 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';*CWE-401;*CWE-772;*CWE-664;BEST CVSS score: '3.3';DESCR 'io_uring async request preparation can import a provided buffer without recycling it before the request is later reimported or completed. Repeated requests using ring mapped provided buffers may leave buffers unavailable and cause request failures or resource exhaustion for the affected process or io_uring instance. For the CVSS the PR:L because exploitation requires a local process that can create and use an io_uring instance with provided buffers. The issue is not network reachable. Impact is limited availability impact and no memory corruption primitive is indicated by the patch.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES SIMPLEFIX LINUS IO_URING LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Local unprivileged trigger. io_uring and provided-buffer registration are normally reachable by an ordinary local process through the io_uring interface. No host-admin capability is indicated by the patch. * +1 Concrete resource-state retention. `io_req_prep_async()` can import a provided buffer but previously did not call `io_kbuf_recycle()`. This can leave the ring-provided buffer unavailable until later handling, causing request failures or limited per-ring resource exhaustion. * +0 Memory corruption. No UAF, double free, stale post-lifetime access, OOB access, refcount mutation, arbitrary write, or controlled corruption is established. * +0 Reliable kernel crash. The patch and supplied context do not establish a kernel crash, panic, or host-wide DoS. * +0 Confidentiality and integrity. There is no demonstrated disclosure, unauthorized modification, security-boundary bypass, or privilege escalation. * +0 Remote reachability. The vulnerable operation is a local io_uring request-preparation path. * No repeated release or refcount operation is established. `io_kbuf_recycle()` commits or returns provided-buffer ring state and is not evidence of a second put or free through a dangling object. 3. Reachability analysis A local process must create and use an io_uring instance configured with ring-mapped supplied buffers and submit request types that enter asynchronous preparation. This is a local data-plane API and does not require network access. The supplied patch does not show a capability check requiring host root, `CAP_SYS_ADMIN`, or another host-admin-equivalent privilege. Therefore, below-host-admin reachability is positively supported for the normal interface and `HostAdminRequired=NO`. No network namespace or user namespace capability is required by the demonstrated path. The complete relevance of namespace scoping is therefore not established and `NamespaceScopedPrivilege=UNKNOWN`. No special hardware, boot parameter, privileged service setup, or difficult race condition is indicated. However, the impact remains limited because the affected resource is the provided-buffer state of the requesting io_uring instance. 4. Primitive and severity interpretation The exact defect is a provided-buffer lifecycle and ring-state handling error. During asynchronous request preparation, a buffer can be imported and then retained instead of being recycled before later request processing reimports it if necessary. This is not an active stale-object lifetime violation. There is no evidence that a freed object remains dereferenced, that a reference count is decremented after object destruction, or that a buffer is accessed outside its valid lifetime. `RealUAF=NO` and `PrimitiveClass=NONE`. The demonstrated consequence is limited request failure or exhaustion of available provided buffers for the affected ring or process. A host-wide memory exhaustion, cross-process impact, privilege escalation, information disclosure, and integrity impact are speculative and are not scored. The issue is not an Important candidate because no kernel-corruption, ownership-boundary, authorization-bypass, or active-object lifetime primitive is established. Automatic downgrade is allowed because the remaining defect is a constrained local resource-state issue without unresolved corruption leverage. 5. One-sentence report phrase An io_uring async preparation path could retain an imported provided buffer without recycling its ring state, allowing a local process to cause request failures or limited provided-buffer exhaustion in its affected io_uring instance. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a local provided-buffer ring-state cleanup defect with limited availability impact and no demonstrated memory-corruption or security-boundary primitive. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: io_uring: fix io_req_prep_async with provided buffers io_req_prep_async() can import provided buffers, commit the ring state by giving up on that before, it'll be reimported later if needed. Reported-by: Muhammad Ramdhan Reported-by: Bing-Jhong Billy Jheng Reported-by: Jacob Soo Fixes: c7fb194 ("io_uring: add support for ring mapped supplied buffers") Signed-off-by: Pavel Begunkov Signed-off-by: Greg Kroah-Hartman Commit: a1b17713b32c75a90132ea2f92b1257f3bbc20f3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a1b17713b32c75a90132ea2f92b1257f3bbc20f3 Changed files: io_uring/io_uring.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a1b17713b32c75a90132ea2f92b1257f3bbc20f3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2025-40364 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-40364 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: Not available The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS score: 3.3 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: unknown Paranoid ActionableScore: 2 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).