From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80829][MODERATE 7.0] ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output() Date: Fri, 04 Sep 2026 17:13:28 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80829 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 558fc4485ecc704edfe7876d6cebae4738ff7ef8 List-Id: CVE: CVE-2026-80829 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output() Commit: 558fc4485ecc704edfe7876d6cebae4738ff7ef8 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=558fc4485ecc704edfe7876d6cebae4738ff7ef8 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80829 Analysis date: Fri, 04 Sep 2026 17:13:28 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80829 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80829 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: MODERATE 7.0 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-2026-80829 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80829 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-195;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'A kernel OOB write in ALSA USB MIDI occurs because snd_usbmidi_novation_output() subtracts a 2-byte header from ep max_transfer without first checking that the endpoint can hold the header and at least one payload byte. A malformed or malicious USB MIDI device can advertise a bulk OUT endpoint with wMaxPacketSize 1, making the transmit count negative and allowing a later memcpy to treat it as a very large size_t length. For the CVSS the PR:N because the attacker does not need an account on the target if the malicious USB device can be attached or supplied to the victim. The issue is not network reachable and normally requires physical USB device access or victim interaction with an untrusted USB MIDI device. Impact is at least denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-80829 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE WRITE OOB USB HARDWARE LINUS KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 4 * Raw paranoid score: 5 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: No floor or cap changed the conservative score. No floor or cap changed the paranoid score. 2. Signal breakdown Conservative positive signals: * +2 Strong corruption primitive. The patch establishes a real kernel OOB write caused by negative length propagation into memcpy after ep->max_transfer becomes smaller than the two byte header requirement. * +1 Firmware or device mediated external influence. A malformed or malicious USB MIDI device can advertise a bulk OUT endpoint with wMaxPacketSize 1. * +1 Reliable kernel crash or strong DoS. The described memcpy with size_t -1 can write far beyond a usb_alloc_coherent buffer and realistically cause kernel memory corruption or crash. Conservative negative signals: * 0 Physical USB access or victim interaction is a major reachability limitation, but I did not subtract a full physical-only penalty because the issue is a concrete kernel OOB write from a malicious peripheral class rather than merely a device-local hang or rare hardware quirk. * 0 No separate race or timing penalty. This is an ordered validation failure, not a timing race. * 0 No host-admin penalty. Host administrator privilege is not established as required for the malicious-device attack model. Paranoid additional signal: * +1 Higher corruption concern. The OOB write length is extremely large after signed-to-unsigned conversion, and the sink is a kernel memcpy into memory beyond a DMA/coherent transfer buffer. This is still grounded in the established OOB write primitive, not a speculative UAF or arbitrary write claim. Important non-awarded signals: * Controlled reclaim is not demonstrated. * Arbitrary or directed kernel write is not demonstrated. * RealUAF is not present. * Remote network reachability is not established. * Confidentiality and integrity are not separately awarded as independent ActionableScore bonuses because no concrete disclosure, credential overwrite, callback control, or protected-object modification is shown. * Extra Availability is not awarded because the same crash/corruption consequence is already counted once. * No concrete repeated release/refcount operation exists. 3. Reachability analysis The most direct attacker model is a malicious or malformed USB MIDI device that presents an invalid endpoint size. The attacker does not need host administrator credentials if they can attach or supply the malicious peripheral and the victim system binds it to ALSA usb-audio. The complete trigger may require the affected Novation-style MIDI output path to become active and data to be transmitted, so victim interaction or a local audio/MIDI application may be needed in practice. This is not network reachable. It is not namespace-scoped. No sysctl, boot parameter, or special kernel debugging configuration is required by the supplied evidence. The hardware requirement is USB MIDI class or compatible device behavior. This is physical/peripheral-mediated exposure, but it is not merely a rare internal hardware feature. 4. Primitive and severity interpretation The exact primitive is an OOB kernel write caused by subtracting a two byte protocol header from an endpoint max transfer size that can be 1. This produces a negative count that later becomes a huge size_t value in memcpy. This is not a UAF and not a cleanup-only stale dereference. It is an active bounds/integer validation failure leading to kernel memory overwrite. The overwrite target begins from a fixed transfer buffer offset, and controlled target selection is not demonstrated. However, the primitive is still stronger than crash-only invalid dereference because the patch-supported path reaches a real memcpy write far beyond the allocated buffer. PrimitiveClass is CLASS_A because a concrete attacker-influenced kernel OOB write is established. ImportantCandidate is YES because kernel memory corruption exists and exploitation leverage beyond DoS is unresolved. AutoDowngradeAllowed is NO because automatically closing this as an ordinary low or moderate device bug would discard a real kernel overwrite primitive. Likely operational severity is Actionable Moderate at minimum, with Strong Important review justified due to the kernel OOB write. The most defensible demonstrated impact is DoS, while privilege escalation or broader C/I impact remains possible but not proven. 5. One-sentence report phrase A malformed USB MIDI device can advertise an endpoint with too small wMaxPacketSize, causing snd_usbmidi_novation_output() to pass a negative transmit length that becomes a huge memcpy size and triggers a kernel OOB write. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a concrete kernel OOB write with a malicious-device trigger and unresolved exploitation leverage beyond crash. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output() Commit: 558fc4485ecc704edfe7876d6cebae4738ff7ef8 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=558fc4485ecc704edfe7876d6cebae4738ff7ef8 Commit description: snd_usbmidi_novation_output() lays out a two-byte header at transfer_buffer[0..1] and passes &transfer_buffer[2] together with a length of ep->max_transfer - 2 to snd_rawmidi_transmit(): count = snd_rawmidi_transmit(ep->ports[0].substream, &transfer_buffer[2], ep->max_transfer - 2); ep->max_transfer comes from the output endpoint's wMaxPacketSize via usb_maxpacket(). A malformed or malicious device can advertise a bulk OUT endpoint with a wMaxPacketSize of 1 - the USB core only clamps this value downwards - so ep->max_transfer becomes 1 and the count argument becomes -1. snd_rawmidi_transmit() passes the negative count on to __snd_rawmidi_transmit_peek(), where "if (count1 > count) count1 = count" leaves count1 negative; get_aligned_size() keeps it negative for a byte-stream substream, so the following memcpy(buffer, ..., count1) runs with a (size_t)-1 length and writes far past the transfer buffer, which was allocated with usb_alloc_coherent(ep->max_transfer). This is the same class of bug that was fixed for snd_usbmidi_akai_output() in commit 0970274 ("ALSA: usb-audio: fix OOB write in snd_usbmidi_akai_output()"); the novation output routine was left unguarded. Bail out when the endpoint cannot hold the two-byte header plus at least one payload byte. Fixes: 1da177e ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Marouane El Moufid Link: https://patch.msgid.link/178749334830.543645.13722252148340572274@espilon.net Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman Changed files: sound/usb/midi.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=558fc4485ecc704edfe7876d6cebae4738ff7ef8 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80829 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80829 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: AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 6.8 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: 4 Paranoid ActionableScore: 5 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: MODERATE KPANIC detected for this report: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).