From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74642][MODERATE REGULAR] ALSA: usb: Fix UAF at delayed release of MIDI2 EPs Date: Sat, 22 Aug 2026 15:14:07 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74642 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: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: d431941825d357be7d9ab0cb7505e3a1963bd89e List-Id: CVE: CVE-2026-74642 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ALSA: usb: Fix UAF at delayed release of MIDI2 EPs Commit: d431941825d357be7d9ab0cb7505e3a1963bd89e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d431941825d357be7d9ab0cb7505e3a1963bd89e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74642 Analysis date: Sat, 22 Aug 2026 15:14:07 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline, manual review required Manual review required: YES Summary: A UAF in ALSA USB MIDI2 endpoint lifetime handling can let a crafted USB MIDI2 device trigger a stale endpoint dereference during delayed release, causing a kernel crash, while privilege escalation remains a theoretical concern without a demonstrated exploit primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74642 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74642 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-2026-74642 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-825;*CWE-664;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A use after free in ALSA USB MIDI2 endpoint lifetime handling can occur because delayed release paths may still reference a snd_ump_endpoint object after that endpoint has already been released. A crafted or repeatedly disconnected USB MIDI2 device could trigger a stale pointer dereference during delayed cleanup, causing a kernel crash and potentially exposing a kernel memory corruption primitive. For the CVSS the PR:N value is used for the paranoid physical attack model because an attacker with physical access to the USB port does not need an account on the target system. The issue is not network reachable. Impact is at least denial of service, and because the bug class is UAF it should be reviewed for possible confidentiality or integrity impact.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review required (with actual score 4) SKIP CVE-2026-74642 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DANGER USB INIT UAF HARDWARE LINUS SYZBOT DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review required**:: ## 2. Signal breakdown * Firmware-mediated external influence: +1 A crafted USB MIDI2 device or USB device emulation can influence the affected ALSA usb-audio path. This is not network reachable. * Memory corruption, weak or indirect corruption candidate: +1 The commit explicitly describes a UAF, but the shown patch only prevents a stale endpoint pointer from being dereferenced during delayed release. No attacker-controlled reclaim, overwrite, type confusion, callback control, or refcount takeover is shown. * Real lifetime corruption: +1 The bug is a real object lifetime issue where a delayed release path can reference an already released UMP endpoint. * Reliable kernel crash / strong DoS: +1 A stale pointer dereference in kernel USB audio cleanup can plausibly cause an Oops or panic. * Availability impact realistic: +1 The practical demonstrated impact is kernel crash or system instability. This is counted conservatively because the impact is host-wide once triggered. * Physical-only or rare hardware-only condition: -2 Realistic triggering requires physical USB access, malicious USB device behavior, or an equivalent local USB emulation/fuzzing setup. Paranoid adjustment: treating the UAF as a stronger memory corruption concern for triage sensitivity raises the score from 3 to 4, but there is still no demonstrated LPE primitive. ## 3. Reachability analysis The likely attacker is someone able to attach or emulate a USB MIDI2 device. No local user account is required in the physical attacker model, but the attacker needs physical USB access or control over a USB device path. Namespaces and containers do not materially improve reachability unless USB device access is delegated into the container. The path is not network reachable. ALSA usb-audio is common, but MIDI2 endpoint handling is more specific and depends on relevant USB descriptors and device behavior. Call-site confidence: medium. The patch shows the lifetime fix and the commit explicitly states delayed release UAF, but the full delayed release call path is not included in the supplied diff. ## 4. Severity interpretation This behaves more like a manual-review Moderate than an Important-class issue. The theoretical concern is kernel UAF memory corruption, which historically deserves manual triage. The realistic evidence in the patch points mainly to stale pointer dereference and crash during delayed cleanup, with no concrete reclaim, write primitive, type confusion, callback hijack, information leak, or privilege escalation path shown. ## 5. One-sentence report phrase A UAF in ALSA USB MIDI2 endpoint lifetime handling can let a crafted USB MIDI2 device trigger a stale endpoint dereference during delayed release, causing a kernel crash, while privilege escalation remains a theoretical concern without a demonstrated exploit primitive. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK. Reason: the issue is explicitly a kernel UAF in a device-driver lifetime path, even though the currently supported practical impact is mainly physical-triggered DoS. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ALSA: usb: Fix UAF at delayed release of MIDI2 EPs Commit: d431941825d357be7d9ab0cb7505e3a1963bd89e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d431941825d357be7d9ab0cb7505e3a1963bd89e Commit description: The recent fix for UAF in ump_to_endpoint() caused another UAF because it tries to dereference the UMP endpoint object, but this might be executed at a delayed context where the endpoint has been already released. Add private_free to clear the associated data for avoiding the further dereference for delayed releases. Fixes: 4a05b2d ("ALSA: usb-audio: fix use-after-free in ump_to_endpoint()") Reported-by: syzbot+565b1138cfbe549d4422@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=565b1138cfbe549d4422 Cc: Link: https://patch.msgid.link/20260808152009.1947835-1-tiwai@suse.de Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman Changed files: sound/usb/midi2.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=d431941825d357be7d9ab0cb7505e3a1963bd89e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74642 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74642 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:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 6.4 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: 4 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).