From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74636][LOW] tracing: Fix race between update_event_fields and, event_define_fields Date: Sat, 22 Aug 2026 12:57:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74636 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 4e39f7b4d9d36508c53e89e6cbc640728df870b5 List-Id: CVE: CVE-2026-74636 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: tracing: Fix race between update_event_fields and, event_define_fields Commit: 4e39f7b4d9d36508c53e89e6cbc640728df870b5 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4e39f7b4d9d36508c53e89e6cbc640728df870b5 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74636 Analysis date: Sat, 22 Aug 2026 12:57:26 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A race between `trace_event_update_all()` and `event_define_fields()` during concurrent privileged module loading can expose an inconsistent tracing event field list and cause a NULL pointer dereference, resulting in a local kernel panic only. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74636 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74636 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: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74636 LOW 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:H/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;**CWE-476;BEST CVSS score: '4.1';DESCR 'A race in the tracing event metadata path can occur when trace_event_update_all walks class fields while event_define_fields is adding new fields during concurrent module loading. The unprotected list traversal can observe an inconsistent field list and dereference an invalid or NULL pointer in update_event_fields, causing a kernel panic. For the CVSS the PR:H is used because reliable triggering normally requires CAP_SYS_MODULE or equivalent privileged module loading rights. The issue is not network reachable and is triggered through local kernel module load activity rather than packet or remote input. Impact is denial of service via kernel crash, with no supported evidence of UAF, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 0) SKIP CVE-2026-74636 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE OOB LOCK TRACE RACE HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 ## 1. ActionableScore * Conservative score: 0 * Paranoid score: 0 * Final recommended bucket: **Ordinary Moderate / Low-like** ## 2. Signal breakdown * Reliable kernel crash / strong DoS: +1 The commit shows a concrete panic in `update_event_fields()` caused by racing list traversal during concurrent module loading. * Hard or unreliable race / special timing required: -1 The bug requires a timing window between two module-load notifier paths on different CPUs. * Requires admin/root/CAP_SYS_MODULE in typical deployments: -2 Reliable triggering requires loading kernel modules, normally requiring `CAP_SYS_MODULE` or equivalent host-root privileges. * Weak corruption / invalid pointer dereference: +0 The demonstrated primitive is an invalid or NULL pointer dereference at address `0x18`. The patch does not show UAF, attacker-controlled reclaim, write-after-free, type confusion, callback control, or arbitrary write. * Availability impact realistic: +0 Not added separately because the crash impact is already counted as strong DoS and there is no persistent corruption or broader availability effect beyond the panic. ## 3. Reachability analysis The bug is locally reachable through concurrent kernel module loading. In normal deployments this requires privileged module-management rights, typically host root or `CAP_SYS_MODULE`. Containers and namespaces usually do not reduce this requirement unless the environment explicitly delegates module loading, which is uncommon and already highly privileged. The affected tracing path is common kernel code, but the trigger condition is not a remote input path and is not reachable through packet traffic or ordinary unprivileged syscalls. Call-site confidence: high. The commit includes the relevant call sequence and the fix directly serializes `trace_event_update_all()` with `event_define_fields()` using `event_mutex`. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like privileged local DoS issue. Theoretical memory-safety concern exists only as an inconsistent list traversal leading to an invalid pointer dereference. There is no realistic evidence of privilege escalation, confidentiality impact, integrity impact, UAF reuse, controlled overwrite, or object replacement. The main practical impact is that a privileged local actor who can already load modules may crash the kernel. ## 5. One-sentence report phrase A race between `trace_event_update_all()` and `event_define_fields()` during concurrent privileged module loading can expose an inconsistent tracing event field list and cause a NULL pointer dereference, resulting in a local kernel panic only. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This is a privileged local race-triggered NULL dereference with no supported LPE, UAF reuse, write primitive, network reachability, or security-boundary bypass. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tracing: Fix race between update_event_fields and, event_define_fields Commit: 4e39f7b4d9d36508c53e89e6cbc640728df870b5 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4e39f7b4d9d36508c53e89e6cbc640728df870b5 Commit description: The following sequence may leads race between event_define_fields() and update_event_fields(): CPU0 (loads module A) CPU1 (loads module B) =============================== =============================== load_module(A) load_module(B) notifier_call_chain notifier_call_chain trace_module_notify trace_module_notify mutex_lock(&event_mutex) trace_event_update_all() trace_module_add_events(A) down_write(&trace_event_sem) __register_event(call_A) __add_event_to_tracers(call_A) event_define_fields(call_A) for each f: list_for_each_entry(field, list_add(&f->link, &class->fields, link) &class->fields) field = class->fields->next; Where access to the class->fields is not protected by the event_mutex in trace_event_update_all(). This produces the following panic: Unable to handle kernel access ... at virtual address 0000000000000018 pc : update_event_fields+0xf8/0x368 Call trace: update_event_fields+0xf8/0x368 trace_event_update_all+0x7c/0x2b4 trace_module_notify+0x4c/0x1dc notifier_call_chain+0x84/0x168 blocking_notifier_call_chain_robust+0x64/0xd4 load_module+0x10c8/0x123c __arm64_sys_finit_module+0x230/0x31c Fix by taking event_mutex in trace_event_update_all() before trace_event_sem. Cc: stable@vger.kernel.org Fixes: b3bc854 ("tracing: Have TRACE_DEFINE_ENUM affect trace event types as well") Link: https://patch.msgid.link/2e5730d2-c631-da41-3a3a-ae35bb4895f3@allwinnertech.com Signed-off-by: Michael Wu Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman Changed files: kernel/trace/trace_events.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=4e39f7b4d9d36508c53e89e6cbc640728df870b5 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74636 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74636 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: Not available The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.1 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: unknown Paranoid ActionableScore: 0 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).