From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74641][IMPORTANT] ALSA: usx2y: bound the hwdep mmap fault offset Date: Sat, 22 Aug 2026 16:16:31 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74641 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: 10a87401fb3148c388e55df0148295b3b137da07 List-Id: CVE: CVE-2026-74641 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: ALSA: usx2y: bound the hwdep mmap fault offset Commit: 10a87401fb3148c388e55df0148295b3b137da07 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=10a87401fb3148c388e55df0148295b3b137da07 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74641 Analysis date: Sat, 22 Aug 2026 16:16:31 -0400 ActionableScore: 7 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: ALSA usx2y hwdep mmap fault handling lacks an offset bound check, allowing a local process with access to the device node to map unintended kernel pages read-write, which can cause a kernel crash and plausibly enable kernel memory disclosure or local privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74641 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74641 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: IMPORTANT Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74641 IMPORTANT CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-823;*CWE-787;CWE-125;CWE-668;BEST CVSS score: '7.8';DESCR 'ALSA usx2y hwdep mmap fault handling can use an attacker controlled page offset without a bounds check and convert an address outside the shared buffer into a mapped struct page. A local process that can open the hwdep node for an attached US-X2Y device can choose the mmap offset and may obtain read-write access to kernel memory outside the intended object. For the CVSS the PR:L is used because triggering requires local code execution and access to the device node, but no special capability check is described. The issue is not network reachable. Impact can include local denial of service, kernel memory disclosure, kernel memory modification, and plausible privilege escalation because the primitive maps unintended kernel pages into user space read-write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) SKIP CVE-2026-74641 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE READ OOB USB HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Local unprivileged trigger: +1 A local process can reach the path by opening the ALSA hwdep node for an attached US-X2Y device. The commit states that no capability check is involved. * Strong LPE plausibility: +2 The bug can map a kernel page outside the intended shared-memory object into user space with read-write permissions. This is a plausible local privilege escalation primitive, not just a crash. * Memory corruption, strong corruption primitive: +2 The attacker controls the mmap page offset and can cause `virt_to_page()` to resolve a page outside the allocated object, then install it into the caller VMA read-write. * Reliable kernel crash / strong DoS: +1 The commit includes an observed kernel Oops when the chosen offset lands in an unpopulated vmemmap region. * Confidentiality impact plausible: +1 Mapping unintended kernel memory into user space can expose kernel data. * Integrity impact plausible: +1 The mapped page is read-write, so unintended kernel memory can potentially be modified. * Availability impact realistic: +1 in paranoid score only A bad offset can produce an Oops, and successful writable mappings can also destabilize the kernel. This is counted only in the paranoid score to avoid double-counting the corruption primitive. * Physical-only or rare hardware-only condition: -2 Exploitation requires an attached US-X2Y device and access to its hwdep node, which limits broad exposure. Call-site confidence: high. The vulnerable fault handlers and their direct behavior are present in the supplied patch context. ## 3. Reachability analysis The trigger is local. A process needs access to the ALSA hwdep character device for an attached US-X2Y device and must reach the state after FPGA image loading through the same node. No capability check is described, so this is not treated as PR:H. Device-node permissions may restrict access in practice, for example to root or an audio-related group, but the kernel path itself is not capability-gated. The issue is not network reachable. Containers and namespaces generally do not help unless the device node is passed into the container. The affected driver is not a broad default attack surface because it depends on uncommon USB audio hardware, but when the device node is accessible the primitive is strong. ## 4. Severity interpretation This behaves more like an Important-class local kernel vulnerability than an ordinary Moderate issue. The realistic exploitation evidence includes both a demonstrated crash path and a stronger primitive where a user-selected mmap offset can expose an unintended kernel page read-write. The main limiting factor is hardware and device-node availability, not weakness of the bug class. Theoretical impact includes local privilege escalation through writable kernel memory exposure. Realistic exploitation still requires careful target-page selection and a reachable device node, so the conservative score remains below Critical-like handling. ## 5. One-sentence report phrase ALSA usx2y hwdep mmap fault handling lacks an offset bound check, allowing a local process with access to the device node to map unintended kernel pages read-write, which can cause a kernel crash and plausibly enable kernel memory disclosure or local privilege escalation. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This should be manually reviewed because the patch fixes a direct read-write kernel page exposure primitive from a local mmap interface, with plausible confidentiality, integrity, and privilege-escalation impact despite the rare-hardware requirement. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ALSA: usx2y: bound the hwdep mmap fault offset Commit: 10a87401fb3148c388e55df0148295b3b137da07 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=10a87401fb3148c388e55df0148295b3b137da07 Commit description: snd_us428ctls_vm_fault() turns the faulting page offset into a kernel address with no bound of any kind: offset = vmf->pgoff << PAGE_SHIFT; vaddr = (char *)(...)->us428ctls_sharedmem + offset; page = virt_to_page(vaddr); get_page(page); vmf->page = page; return 0; snd_us428ctls_mmap() checks only the length of the mapping, never the offset, and us428ctls_sharedmem is a single page from alloc_pages_exact(). For a character device file_mmap_size_max() returns ULONG_MAX, so the mm layer imposes no ceiling either. Every page offset above zero resolves to a struct page outside the object, and the handler installs it into the caller's address space read-write; the vma is not marked read-only. The caller picks the page frame with a single mmap() argument and gets read-write access to a page of kernel memory it does not own; an offset that lands in an unpopulated vmemmap region oopses instead. A process that can open the hwdep node of an attached US-X2Y reaches this after loading the FPGA image through the same node; no capability check is involved. On 7.2.0-rc5 (arm64), mmap() with a large offset: Unable to handle kernel paging request at virtual address fffffdffc45d5ac8 pc : snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y] Call trace: snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y] __do_fault __handle_mm_fault handle_mm_fault el0_da Reject any offset outside the shared region. The pcm hwdep handler in usx2yhwdeppcm.c computes its address the same way and needs the same bound. Discovered by XBOW, triaged by Baul Lee Fixes: 1da177e ("Linux-2.6.12-rc2") Reported-by: Federico Kirschbaum Reported-by: Baul Lee Cc: stable@vger.kernel.org Signed-off-by: Baul Lee Link: https://patch.msgid.link/20260805013445.38283-1-baul.lee@xbow.com Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman Changed files: sound/usb/usx2y/usX2Yhwdep.c sound/usb/usx2y/usx2yhwdeppcm.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=10a87401fb3148c388e55df0148295b3b137da07 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74641 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74641 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:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 6 Paranoid ActionableScore: 7 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).