From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45949][MODERATE REGULAR] hwrng: core - use RCU and work_struct to fix race condition [ Upstream Date: Wed, 27 May 2026 09:05:16 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45949 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: d5b7730f06994499632026c30e38e0317c4569e2 List-Id: CVE: CVE-2026-45949 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: hwrng: core - use RCU and work_struct to fix race condition [ Upstream Commit: d5b7730f06994499632026c30e38e0317c4569e2 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5b7730f06994499632026c30e38e0317c4569e2 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45949 Analysis date: Wed, 27 May 2026 09:05:16 -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-2026-45949 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45949 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-2026-45949 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';CWE-362;*CWE-416;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.2';DESCR 'A race in the hwrng core can leave the global hwrng_fill task pointer stale across fast hwrng_register and hwrng_unregister sequences. This can make hwrng_unregister call kthread_stop on the same task twice or on a task_struct that has already been freed, producing a real use after free in a kernel thread lifetime path. For the CVSS the PR:H is used because reliable triggering normally requires privileged hardware RNG device management, module unload, driver unbind, or hotplug control rather than ordinary local user access. The issue is not network reachable and reading from /dev/hwrng alone is not the relevant trigger path. Impact is primarily availability through kernel warning or crash. Limited confidentiality and integrity impact are kept only for the paranoid interpretation because the bug is a real UAF, but the patch does not show controlled reclaim, arbitrary write, or a strong LPE primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) YES LOCK DEADLOCK INIT RACE UAF DMAorINTERRUPT HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended**:: 2. Signal breakdown * Generic memory corruption, strong corruption primitive: +2. The commit explicitly describes a use-after-free on a freed task_struct via kthread_stop(). * Real lifetime corruption: +1. The bug is a race in task/thread lifetime handling where hwrng_fill can remain stale after unregister. * Reliable kernel crash / strong DoS: +1. The reported refcount_t warning and UAF path can plausibly crash or destabilize the kernel. * Privileged kernel/device-management memory corruption path: +1. The vulnerable path is hwrng register/unregister, driver remove, hotplug, or module/device lifecycle handling. * Firmware-mediated or device-mediated influence: +1 in paranoid scoring. In virtio_rng or hotplug-like deployments, device removal may be influenced externally by host/device management, but this is not ordinary network reachability. * Hard or unreliable race / special timing required: -1. The issue depends on close timing between hwrng_register(), hwrng_unregister(), thread startup, and task cleanup. * Requires admin/root/device-management privileges in typical deployments: -2. Reliable triggering normally requires module unload, driver unbind, device removal, or hotplug control. * Constrained primitive / no attacker-controlled payload: -1. The patch shows a real UAF, but not controlled reclaim, arbitrary write, object confusion, or a demonstrated LPE path. * Availability impact realistic: +1. DoS is the main practical impact. 3. Reachability analysis The bug is not reachable through normal /dev/hwrng reads alone. It is triggered by hwrng device lifecycle operations such as fast register/unregister, driver remove, module unload, or hotplug paths like virtrng_remove(). In ordinary deployments this requires host-level administrative or device-management privileges. Containers and user namespaces generally do not lower this requirement unless a container or service is explicitly delegated device unbind or module management control. The path may be present on systems using hardware RNG or virtio-rng, but realistic attacker control is limited. 4. Severity interpretation This is more serious than a simple warning or logic bug because the patch fixes a real UAF on task_struct lifetime. However, it behaves more like a borderline Moderate issue than an Important-class vulnerability because the trigger is privileged, timing-dependent, and lacks evidence of controlled memory reuse or a strong privilege-escalation primitive. Theoretical memory corruption exists. Realistic exploitation evidence mainly supports kernel crash or instability. 5. One-sentence report phrase A race in hwrng register and unregister handling can leave hwrng_fill pointing to a freed task_struct, allowing privileged device lifecycle operations to trigger a task lifetime UAF and kernel crash. 6. Manual review recommendation MANUAL CHECK REQUIRED The patch explicitly fixes a real race-based use-after-free, even though practical exploitability appears constrained by privileged device-management reachability and lack of a demonstrated LPE primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: hwrng: core - use RCU and work_struct to fix race condition [ Upstream Commit: d5b7730f06994499632026c30e38e0317c4569e2 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5b7730f06994499632026c30e38e0317c4569e2 Changed files: lib/refcount.c drivers/char/hw_random/core.c include/linux/hw_random.h 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=d5b7730f06994499632026c30e38e0317c4569e2 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45949 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45949 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:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 5.2 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).