From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-68201][IMPORTANT] ALSA: timer: drain a slave's callback before its master detaches it Date: Mon, 10 Aug 2026 13:10:39 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-68201 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: 5 X-AL-KERNEL-Commit: cd461bcfcdf8d6b6b5365941c1d3859f8bc77aa0 List-Id: CVE: CVE-2026-68201 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: ALSA: timer: drain a slave's callback before its master detaches it Commit: cd461bcfcdf8d6b6b5365941c1d3859f8bc77aa0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd461bcfcdf8d6b6b5365941c1d3859f8bc77aa0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68201 Analysis date: Mon, 10 Aug 2026 13:10:39 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A local use-after-free in the ALSA timer close path can occur when a master timer detaches slave timers without draining their in-flight callbacks, allowing a freed slave timer instance to be used by a live callback and causing at least a kernel crash with possible privilege escalation concerns. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68201 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68201 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-2026-68201 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur in the ALSA timer close path because snd_timer_close_locked() drained only the closing master timer instance callback and did not drain callbacks running on its slave timer instances. When the master is closed, remove_slave_links() can clear the slave timer pointer, and the later slave close path can skip draining because timer is NULL. A slave callback that is already in flight may then continue to run after the slave timer instance has been freed. For the CVSS the PR:L is used because a local user or process with access to ALSA timer interfaces can create and close timer instances and does not need full administrator privileges in common desktop or audio group deployments. The issue is not network reachable. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use after free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES INIT UAF TIMER HARDWARE LINUS KPANIC YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. ALSA timer interfaces can be reachable by local users with sound device access, often via desktop audio group policy. * Generic memory corruption, strong corruption primitive: +2. The commit explicitly describes a use-after-free where a slave timer instance can be freed while its callback is still running. * Real lifetime corruption: +1. This is a lifetime bug involving close, detach, callback drain, and later free. * Reliable kernel crash / strong DoS: +1. A live callback using a freed timer instance is a realistic kernel crash path. * Broad/default/common subsystem exposure: +1. ALSA is commonly enabled on desktop and workstation kernels, though access depends on device permissions. * Hard or unreliable race / special timing required: -1. Triggering depends on timing between master close, slave detach, and an in-flight callback. Paranoid additional signal: * Privilege escalation plausible: +2. The bug is a kernel UAF in a callback/lifetime path. No exploit primitive is demonstrated, but callback execution after free is strong enough to require Important-class manual review. Not counted: * Remote reachable: +0. No network path. * Confidentiality or integrity impact as demonstrated: +0 conservative. The patch proves UAF, not a concrete read/write primitive. * Availability impact realistic: not separately added to avoid double-counting the strong DoS signal. Call-site confidence: high. The patch and commit directly describe the close path, slave detach behavior, ack list handling, and the missing callback drain. ## 3. Reachability analysis A local process with access to ALSA timer functionality can potentially create master and slave timer instances and race close or detach behavior against callback execution. Full host root is not inherently required in common desktop-style deployments where sound devices are delegated to local users or an audio group. In hardened server or container deployments, reachability may be reduced if ALSA devices are absent or not exposed. Namespaces do not by themselves make this remote, but containers with passed-through sound devices could lower practical isolation. The bug is not network reachable. ## 4. Severity interpretation This is more than an ordinary Moderate because the patch explicitly fixes a kernel use-after-free, not just a warning, leak, or validation issue. Realistic demonstrated impact is local DoS through kernel crash. Theoretical impact includes possible privilege escalation because the freed object may still be used by an in-flight callback, but the provided patch does not demonstrate controlled reclaim, object replacement, or arbitrary write. Conservative handling is Actionable Moderate. Paranoid handling is a Strong Important candidate for manual review. ## 5. One-sentence report phrase A local use-after-free in the ALSA timer close path can occur when a master timer detaches slave timers without draining their in-flight callbacks, allowing a freed slave timer instance to be used by a live callback and causing at least a kernel crash with possible privilege escalation concerns. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: explicit kernel UAF plus callback/lifetime race. Even without a demonstrated LPE primitive, this class should not be auto-closed because exploitability depends on allocator reuse and timing details that require manual source-level review. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ALSA: timer: drain a slave's callback before its master detaches it Commit: cd461bcfcdf8d6b6b5365941c1d3859f8bc77aa0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd461bcfcdf8d6b6b5365941c1d3859f8bc77aa0 Commit description: snd_timer_close_locked() drains the closing instance's own in-flight callback (IFLG_CALLBACK) before freeing it, but not its slaves'. When a master instance is closed, remove_slave_links() clears each slave's ->timer; the slave's own close then reads timer == NULL and takes the branch that skips the drain entirely (snd_timer_stop_slave() also no-ops on a NULL timer). So a slave whose callback is still running when the master is closed is freed underneath the live callback, leading to use-after-free. Drain the slaves too before remove_slave_links() severs them. snd_timer_stop() has already taken this instance off the active list, so no new slave callback can be queued. Take the slaves off the ack list so a pending one can't fire either, then wait for any that is already in flight. Fixes: 3774591 ("ALSA: timer: Introduce virtual userspace-driven timers") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Norbert Szetei Signed-off-by: Takashi Iwai Link: https://patch.msgid.link/D26598EB-DBF7-4D76-9F71-8E4BD59822D4@doyensec.com Signed-off-by: Greg Kroah-Hartman Changed files: sound/core/timer.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=cd461bcfcdf8d6b6b5365941c1d3859f8bc77aa0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68201 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68201 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:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 5 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).