From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74497][MODERATE 7.0] ALSA: usb-audio: Clamp frame size in implicit-feedback mode Date: Sat, 15 Aug 2026 18:38:24 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74497 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 56ac3e7c90f6b45969c3fd07a98fad760ffd6901 List-Id: CVE: CVE-2026-74497 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ALSA: usb-audio: Clamp frame size in implicit-feedback mode Commit: 56ac3e7c90f6b45969c3fd07a98fad760ffd6901 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56ac3e7c90f6b45969c3fd07a98fad760ffd6901 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74497 Analysis date: Sat, 15 Aug 2026 18:38:24 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: A malicious USB audio device can send an oversized implicit feedback sync packet that causes ALSA usb-audio to queue playback packet sizes above the endpoint frame limit, leading to at least denial of service and a constrained memory-safety concern. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74497 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74497 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74497 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-1284;*CWE-20;*CWE-787;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.7';DESCR 'An oversized implicit feedback sync packet from a connected USB audio device can make snd_usb_handle_sync_urb() calculate a frame count larger than ep maxframesize. That unbounded frame count is stored in out_packet packet_size and can later enter the playback endpoint queue, potentially causing transfers beyond the endpoint hardware frame limit. For the CVSS the PR:N because the attacker only needs control of a connected USB audio device and does not need a local user account on the victim system. The issue is not network reachable and requires physical or device level access. Impact is at least denial of service through broken USB audio transfer handling or a kernel fault. For the paranoid score, limited confidentiality or integrity impact is kept because the bug is an unchecked size propagation into transfer sizing logic, but the patch does not prove a reliable privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES USB SIMPLEFIX HARDWARE LINUS PACKET INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Firmware/device-mediated external influence: +1. A connected USB audio device controls the implicit feedback sync packet length. * Reliable kernel crash / strong DoS: +1. The unbounded frame count can enter playback endpoint queueing and may drive transfers beyond endpoint limits. * Broad/common subsystem exposure: +1. USB audio is a common desktop and workstation subsystem. * Physical-only or device-only condition: -2. The attacker needs a malicious or compromised USB audio device, not network access. * Availability impact realistic: +1. A malformed device can plausibly break audio transfer handling or trigger a kernel fault. Paranoid additional signals: * Constrained kernel transfer/buffer sizing corruption candidate: +1. The bug propagates an unchecked device-controlled size into transfer sizing logic, but no arbitrary target or payload is shown. * Privileged kernel/device-management path: +1. The affected path is kernel USB audio endpoint handling, close to device transfer management. * Confidentiality impact plausible: +1. Only for paranoid scoring, because oversized transfer sizing could theoretically affect adjacent kernel/device data handling. * Integrity impact plausible: +1. Only for paranoid scoring, due to possible constrained memory safety impact, not a proven LPE primitive. * Constrained primitive uncertainty: -1. The patch does not show attacker-controlled overwrite target, UAF, object replacement, or arbitrary write. Net result: conservative 3, paranoid 5. ## 3. Reachability analysis The bug can be triggered by a connected USB audio device that sends an oversized implicit feedback sync packet. No local user account is required on the victim, but the attack is not network reachable and requires physical access, malicious peripheral access, or a compromised device path. Containers and namespaces do not materially reduce the physical/device requirement. The subsystem is commonly available, but the affected path requires USB audio implicit-feedback behavior, so exposure depends on the device and active audio stream configuration. Call-site confidence: medium. The patch shows the unchecked value being stored into `out_packet->packet_size[i]`, and the commit states that it propagates to the playback endpoint queue, but the full downstream transfer construction path is not included. ## 4. Severity interpretation This is more than an ordinary low-risk validation fix because device-controlled packet sizing crosses into kernel playback transfer preparation. Realistically, the demonstrated impact is DoS from invalid transfer sizing or kernel fault. Theoretical memory corruption concern is limited and constrained. The patch does not demonstrate UAF, arbitrary write, attacker-controlled reclaim, callback control, or a strong privilege-escalation primitive. Therefore this is best treated as Actionable Moderate for manual triage, not a strong Important candidate by default. ## 5. One-sentence report phrase A malicious USB audio device can send an oversized implicit feedback sync packet that causes ALSA usb-audio to queue playback packet sizes above the endpoint frame limit, leading to at least denial of service and a constrained memory-safety concern. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the issue is device-reachable and involves unchecked device-controlled transfer sizing in kernel USB audio code, but the provided patch does not prove a strong memory corruption or privilege escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ALSA: usb-audio: Clamp frame size in implicit-feedback mode Commit: 56ac3e7c90f6b45969c3fd07a98fad760ffd6901 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56ac3e7c90f6b45969c3fd07a98fad760ffd6901 Commit description: snd_usb_handle_sync_urb() scales received sync packet sizes by the sender's stride and stores the result directly in out_packet->packet_size[i]. If a connected USB device sends an oversized sync packet, this frame count can exceed ep->maxframesize. The un-clamped frame count then propagates to the playback endpoint queue, potentially driving packet transfers beyond the endpoint's hardware frame limits. Cap the calculated frame count against ep->maxframesize in snd_usb_handle_sync_urb() to prevent oversized packets from entering the playback queue. Fixes: 28acb12 ("ALSA: usb-audio: use sender stride for implicit feedback") Cc: stable@vger.kernel.org Assisted-by: Jetski:Gemini-3.6-Flash Signed-off-by: Sonali Pradhan Link: https://patch.msgid.link/20260728202432.2354994-1-sonalipradhan@google.com Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman Changed files: sound/usb/endpoint.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=56ac3e7c90f6b45969c3fd07a98fad760ffd6901 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74497 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74497 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:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 5.7 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: 3 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: NO 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).