From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64235][MODERATE REGULAR] x86/ftrace: Relocate %rip-relative percpu refs in dynamic trampolines [ Upstream Date: Fri, 24 Jul 2026 13:01:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64235 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: 1 X-AL-KERNEL-Commit: 8093442a2d1d4b42b9340a86023ccb2afb30b93a List-Id: CVE: CVE-2026-64235 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: x86/ftrace: Relocate %rip-relative percpu refs in dynamic trampolines [ Upstream Commit: 8093442a2d1d4b42b9340a86023ccb2afb30b93a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8093442a2d1d4b42b9340a86023ccb2afb30b93a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64235 Analysis date: Fri, 24 Jul 2026 13:01:25 -0400 ActionableScore: 4 ActionableScore lower bound: 1 Actionable bucket: Borderline manual-review Moderate. Actionable Moderate only if delegated tracing is reachable Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64235 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64235 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-2026-64235 MODERATE 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:L/UI:N/S:U/C:L/I:L/A:H';CWE-682;*CWE-787;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A dynamic ftrace trampoline can contain RIP relative percpu references copied from the original ftrace caller code. If the displacement is not relocated for the new trampoline address, the call_depth accounting instruction can write to the wrong kernel address and trigger a supervisor page fault and kernel panic. The practical trigger requires a specific affected x86 configuration with CONFIG_CALL_DEPTH_TRACKING and retbleed stuffing enabled, plus the ability to register or enable dynamic tracing such as kprobe based tracing. For the CVSS the PR:L is used for the paranoid score because a local user with delegated tracing or reduced administration rights may be able to reach the interface, while typical systems require administrator level tracing access. The issue is not network reachable. Impact is at least local denial of service, and in the worst still defensible interpretation may include limited confidentiality or integrity impact due to an invalid kernel memory write candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual-review Moderate. Actionable Moderate only if delegated tracing is reachable (with actual score 3) YES OOB TRACE BPF KERNEL_PANIC_PLUS_UAF HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=1 1. ActionableScore * Conservative score: 1 * Paranoid score: 4 * Final recommended bucket: **Borderline manual-review Moderate. Actionable Moderate only if delegated tracing is reachable**:: 2. Signal breakdown * Weak or indirect corruption candidate: +1. The bad RIP-relative relocation can make the generated ftrace trampoline write to an unintended kernel address via the call-depth accounting instruction. This is not an arbitrary write because target and payload control are not demonstrated. * Reliable kernel crash / strong DoS: +1. The commit provides a simple reproducer that reaches a supervisor write page fault and kernel panic. * Availability impact realistic: +1 in paranoid scoring only. The crash is host-wide and reproducible after the tracing setup. * Local trigger / delegated local trigger: +1 in paranoid scoring only. Typical access is privileged, but delegated tracing or reduced-admin environments can make this closer to PR:L. * Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2 for conservative scoring. Writing kprobe events and enabling tracing normally requires root or tracing privileges. * Rare or configuration-dependent condition: -1. The issue requires CONFIG_CALL_DEPTH_TRACKING, a retbleed-affected x86 platform, retbleed stuffing, and dynamic ftrace trampoline registration. * No strong LPE signal. There is no shown attacker-controlled reclaim, arbitrary write, type confusion, callback control, or controlled target selection. 3. Reachability analysis The practical trigger is local and normally requires privileged access to tracingfs or equivalent tracing control. A reduced-capability service, container setup, or delegated tracing policy could lower practical privileges, but this is not the common default. The path is not network reachable. The bug is configuration-specific to affected x86 retbleed mitigation and call-depth tracking setups. Call-site confidence: high, because the patch and commit directly identify create_trampoline(), the copied CALL_DEPTH_ACCOUNT instruction, and the resulting faulting write. 4. Severity interpretation This behaves primarily as a reliable local DoS on a specific x86 tracing configuration. The theoretical concern is an invalid kernel write caused by an unrelocated RIP-relative percpu reference, but the patch does not show enough control over the destination or written value to treat it as a strong privilege-escalation primitive. Conservative handling is ordinary Moderate / Low-like due to privileged reachability. Paranoid handling is borderline manual-review Moderate because invalid kernel writes in generated trampoline code can be under-triaged. 5. One-sentence report phrase A missing relocation for RIP-relative percpu references in x86 dynamic ftrace trampolines can cause the call-depth accounting instruction to access the wrong kernel address, leading to a reproducible local kernel panic on affected retbleed call-depth-tracking configurations. 6. Manual review recommendation MANUAL CHECK REQUIRED. The observed impact is DoS, but the failure mode is an unintended kernel write from generated executable trampoline code, so it should not be auto-closed without confirming whether target control or mapped-address corruption is possible. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: x86/ftrace: Relocate %rip-relative percpu refs in dynamic trampolines [ Upstream Commit: 8093442a2d1d4b42b9340a86023ccb2afb30b93a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8093442a2d1d4b42b9340a86023ccb2afb30b93a Changed files: arch/x86/kernel/ftrace.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=8093442a2d1d4b42b9340a86023ccb2afb30b93a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64235 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64235 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:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 5.8 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: 1 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).