From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80920][MODERATE REGULAR] io_uring: defer eventfd signaling when queued from a wakeup handler [ Upstream Date: Wed, 09 Sep 2026 12:51:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80920 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: e22f4494cc9487d326e5e3067f33dea7c1e442b2 List-Id: CVE: CVE-2026-80920 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: io_uring: defer eventfd signaling when queued from a wakeup handler [ Upstream Commit: e22f4494cc9487d326e5e3067f33dea7c1e442b2 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e22f4494cc9487d326e5e3067f33dea7c1e442b2 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80920 Analysis date: Wed, 09 Sep 2026 12:51:25 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80920 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80920 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-2026-80920 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80920 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;CWE-662;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'io_uring can signal the CQ ring eventfd inline while task_work is queued from a waitqueue wakeup handler where an arbitrary provider waitqueue lock is already held. If the eventfd notification feeds back through epoll, the wake chain can recurse into the same locking context and cause a deadlock or soft lockup. For the CVSS the PR:L is used because a local user or local process must create and drive the io_uring, eventfd, epoll, and wakeup interaction, but full administrator privileges are not normally required when io_uring is available. The issue is not directly network reachable because it is triggered through local kernel interfaces rather than remote packet processing. Impact is denial of service through a stuck wakeup or task_work path. No confidentiality or integrity impact is assigned because the patch context indicates a locking and reentrancy problem, not a memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES UAF IO_URING DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH YES NO guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 3 * Conservative score: 3. No floor or cap applied. * Raw paranoid score: 4 * Paranoid score: 4. No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Conservative positive signals: * +1 Local unprivileged trigger. io_uring, eventfd, epoll, poll, futex, and waitid interactions are local user reachable on systems where io_uring is enabled. * +1 Reliable kernel DoS / strong DoS. The patch describes recursive wakeup through epoll while a waitqueue lock is held, which can cause deadlock or soft lockup. * +1 Broad local kernel interface exposure. io_uring plus eventfd and epoll are broadly deployed local kernel interfaces, even though this exact DEFER_TASKRUN path is more specific. Paranoid additional signal: * +1 Local high-control kernel API interaction. A local process can shape the io_uring, eventfd, epoll, and waitqueue topology relevant to the recursive wake path. This is not memory-corruption control, but it can make the DoS trigger more actionable. Negative signals: * No -1 hard race penalty. The issue is reentrancy through a wake chain, not a proven narrow one-shot race. * No -2 host-admin penalty. Host-admin-equivalent privilege is not required for ordinary io_uring use when the interface is available. Important non-awarded signals: * No UAF or stale post-lifetime object use is established. * No concrete repeated release/refcount mutation exists. * No controlled reclaim is demonstrated. * No arbitrary or directed kernel write is demonstrated. * No confidentiality or integrity impact is awarded. * No remote reachability is established. * No extra Availability point is awarded because the same deadlock or soft lockup is already counted as DoS. * No Strong LPE or Weak LPE concern is awarded because the patch indicates a locking and reentrancy problem, not a memory corruption or authorization primitive. 3. Reachability analysis The evaluated attacker is a local below-host-admin process. The attacker needs to create and drive an io_uring setup using DEFER_TASKRUN behavior together with eventfd and epoll feedback, and trigger task_work queuing from waitqueue wakeup handlers such as poll, futex, or waitid paths. Host administrator privilege is not positively required. The path is local and syscall based, not namespace-capability based, so NamespaceScopedPrivilege is NO rather than YES. There is no direct packet-processing or remote network trigger. Prior privileged setup is not inherent except for systems where io_uring is administratively disabled or restricted. No special hardware is required. The trigger depends on a specific interaction of local kernel interfaces, but the patch does not establish a narrow externally uncontrollable timing race. 4. Primitive and severity interpretation The exact primitive is lock reentrancy / wakeup recursion: io_req_local_work_add() could signal the CQ ring eventfd inline while called from a wakeup handler holding an arbitrary waitqueue lock. eventfd signaling can feed back into epoll and recurse into the same lock context. This is not active structured UAF and not fixed stale storage. It is a Class C DoS-style synchronization bug. The demonstrated consequence is deadlock, soft lockup, or a stuck task_work / wakeup path. The speculative consequence beyond DoS is weak because no memory corruption, stale object reuse, refcount mutation, security boundary bypass, information disclosure, or write primitive is established. ImportantCandidate is NO because no Class A or meaningful Class B primitive exists. ManualReview is RECOMMENDED because io_uring plus eventfd plus epoll locking interactions are subtle and locally reachable. AutoDowngradeAllowed is YES because the established primitive is DoS-only and no unresolved corruption or boundary-bypass primitive would be lost by downgrade. Likely operational severity is borderline to actionable Moderate depending on product exposure to untrusted local users and whether io_uring is enabled. 5. One-sentence report phrase A local io_uring user can trigger inline eventfd signaling from a waitqueue wakeup handler and recurse through epoll while a provider waitqueue lock is held, causing a deadlock or soft lockup DoS without evidence of memory corruption or privilege escalation. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the issue is local and DoS-only, but io_uring eventfd epoll wakeup recursion is complex enough that product-specific io_uring availability and local-user exposure should be checked before automatic closure. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: io_uring: defer eventfd signaling when queued from a wakeup handler [ Upstream Commit: e22f4494cc9487d326e5e3067f33dea7c1e442b2 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e22f4494cc9487d326e5e3067f33dea7c1e442b2 Changed files: include/linux/io_uring_types.h io_uring/eventfd.c io_uring/eventfd.h io_uring/futex.c io_uring/io_uring.c io_uring/poll.c io_uring/waitid.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=e22f4494cc9487d326e5e3067f33dea7c1e442b2 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80920 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80920 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:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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).