From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74500][MODERATE REGULAR] ALSA: usb-audio: fix stack info leak in RME Digiface status Date: Sat, 15 Aug 2026 13:04:41 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74500 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: b3a346d5c99dd73cf84711f2a43e42691990efd2 List-Id: CVE: CVE-2026-74500 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ALSA: usb-audio: fix stack info leak in RME Digiface status Commit: b3a346d5c99dd73cf84711f2a43e42691990efd2 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3a346d5c99dd73cf84711f2a43e42691990efd2 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74500 Analysis date: Sat, 15 Aug 2026 13:04:41 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline Moderate. Manual review recommended Manual review required: YES Summary: A local user with access to the affected ALSA control device may read limited kernel stack residue from the RME Digiface USB status path when the device returns a short successful control-IN response. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74500 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74500 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 REGULAR 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-2026-74500 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';CWE-908;*CWE-200;CWE-201;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'A kernel stack information leak exists in the ALSA USB audio RME Digiface status path because snd_rme_digiface_read_status() used an uninitialized on stack 16 byte buffer. A short successful USB control IN transfer can leave trailing words unchanged, and those words can later be exposed through ALSA control reads from /dev/snd/controlC*. For the CVSS the PR:L is used because a local user or process must read the ALSA control interface to receive the leaked data, while the short transfer condition depends on the specific USB device behavior. The issue is not network reachable. Impact is confidentiality loss only. Integrity and availability are not directly affected. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate. Manual review recommended (with actual score 3) YES USB LEAK HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Borderline Moderate. Manual review recommended**:: ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 Unprivileged local users may read ALSA control data via `/dev/snd/controlC*` depending on device permissions. * Firmware-mediated external influence: +1 The leak depends on USB device behavior, specifically a short successful vendor control-IN transfer. * Confidentiality impact plausible: +1 The bug can expose up to 16 bytes of kernel stack residue through ALSA status controls. Subtracting signals: * Rare AND difficult-to-reach subsystem/configuration: -1 The issue is specific to the RME Digiface USB mixer quirk path and requires the affected hardware or a device behaving like it. No signals awarded for: * Generic memory corruption: no UAF, OOB write, double-free, or type confusion is shown. * Privilege escalation plausible: no write primitive or object lifetime corruption is shown. * Reliable DoS: no crash or availability impact is described. * Remote reachability: this is not network-triggerable. ## 3. Reachability analysis The issue is reachable by a local user or local process that can read the ALSA control interface for the affected USB audio device. The leak requires the RME Digiface status path and a short successful USB control-IN response, so practical triggering depends on device behavior or a malicious or non-conforming USB device. Namespaces and containers may matter if `/dev/snd/controlC*` is passed into a container or made accessible to a less trusted workload. In normal desktop or audio workstation setups, ALSA control devices may be readable by users in an audio-related group, but the affected hardware is not broadly present by default. ## 4. Severity interpretation This behaves like a low-to-borderline Moderate information disclosure issue, not an Important-class kernel memory corruption bug. The theoretical security relevance is that kernel stack bytes can help bypass address randomization or aid a later exploit chain, but the patch only supports a bounded stack disclosure primitive and does not show integrity impact, availability impact, or direct privilege escalation. The paranoid score is slightly higher because kernel stack disclosure to unprivileged users should not be auto-dismissed without checking product exposure and device permissions. ## 5. One-sentence report phrase A local user with access to the affected ALSA control device may read limited kernel stack residue from the RME Digiface USB status path when the device returns a short successful control-IN response. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: this is a real kernel stack information leak with local userspace exposure, but it is bounded, device-specific, not network reachable, and does not show a direct memory corruption or privilege-escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ALSA: usb-audio: fix stack info leak in RME Digiface status Commit: b3a346d5c99dd73cf84711f2a43e42691990efd2 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3a346d5c99dd73cf84711f2a43e42691990efd2 Commit description: snd_rme_digiface_read_status() reads a four-word status block from the device into an uninitialised on-stack __le32 buf[4] and, whenever the vendor control-IN transfer does not return a negative error, copies all four words into the caller's status[]. snd_usb_ctl_msg() copies the full requested size back into the caller's buffer regardless of how many bytes the data stage actually delivered: buf = kmemdup(data, size, GFP_KERNEL); err = usb_control_msg(dev, pipe, request, requesttype, value, index, buf, size, timeout); memcpy(data, buf, size); usb_control_msg() returns the transferred length on a short control-IN, which is a non-negative value, and writes only that many bytes. The remainder of the copy back is the kmemdup()ed image of the caller's buffer, so a device answering with a short data stage leaves the trailing words of buf[] holding leftover kernel stack. The only guard in the caller is err < 0, so those words are stored into status[]. They then reach user space: snd_rme_digiface_get_status_val() selects a 16-bit halfword of status[] per the control's reg/mask, and the eight Digiface status controls together expose the whole 16-byte frame to an unprivileged reader of /dev/snd/controlC*. Zero-initialise the buffer so a short read yields zeros instead of stack residue. This mirrors snd_rme_get_status1(), which already clears its output word before the same kind of vendor read. Discovered by XBOW, triaged by Baul Lee Fixes: 611a96f ("ALSA: usb-audio: Add mixer quirk for RME Digiface USB") Reported-by: Federico Kirschbaum Reported-by: Baul Lee Cc: stable@vger.kernel.org Signed-off-by: Baul Lee Link: https://patch.msgid.link/20260726065020.46070-1-baul.lee@xbow.com Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman Changed files: sound/usb/mixer_quirks.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=b3a346d5c99dd73cf84711f2a43e42691990efd2 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74500 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74500 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:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N The Best / paranoid CVSS score: 4.7 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: 2 Paranoid ActionableScore: 3 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 REGULAR 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).