From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99163][MODERATE 7.0] tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields Date: Thu, 29 Oct 2026 00:47:57 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99163 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 1f36e4ddd05d540f363dbaa4c23042549f15b3ef List-Id: CVE: CVE-2026-99163 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields Commit: 1f36e4ddd05d540f363dbaa4c23042549f15b3ef Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1f36e4ddd05d540f363dbaa4c23042549f15b3ef Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99163 Analysis date: Thu, 29 Oct 2026 00:47:57 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: A malformed tracing histogram can cause an attacker-supplied 64-bit scalar to be dereferenced as a kernel stacktrace pointer, enabling a kernel crash and an unconfirmed disclosure possibility. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99163 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99163 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 7.0 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-2026-99163 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99163 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H';CWE-843;*CWE-20;CWE-125;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7.1';DESCR 'A synthetic stacktrace field could incorrectly accept an ordinary signed 8 byte histogram scalar because validation fell through to generic size and signedness checks. The scalar was then treated as a kernel stacktrace pointer and dereferenced by get_field_size and trace_stack. This provides an invalid kernel read primitive with a direct kernel crash risk and a plausible but not fully demonstrated information disclosure path through tracing output. No write primitive or evidence of integrity modification is present. For the CVSS the PR:H base value reflects that configuring histogram and synthetic event triggers normally requires privileged tracefs access. For the CVSS the PR:L paranoid value covers deployments that delegate tracing control to a restricted service account or reduced capability administrator. The issue is local and deterministic after a malicious trigger configuration is accepted. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.1 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 3.8 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE WARNONLY TRACE LEAK LINUS KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 3. * Conservative score: 5. Manual-review safety floor applied: 3 -> 5 for a specific attacker-influenced semantic reinterpret that drives kernel memory access. * Raw paranoid score: 4. * Paranoid score: 5. The same safety floor subsumes the additional semantic-reinterpret concern. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 — Strong semantic reinterpret: an accepted signed 64-bit scalar is subsequently treated as a kernel stacktrace pointer and dereferenced by `get_field_size()` and `trace_stack()`. * +1 — Reliable kernel crash/strong DoS is plausible from deterministic dereference of an attacker-chosen invalid address. * Paranoid +1 — The semantic mismatch directly affects kernel memory access, satisfying the extra reinterpretation concern. * No privilege penalty: privileged tracefs configuration is suggested, but effective host-administrator privilege for the complete trigger is not positively established. * No confidentiality point: tracing output could plausibly expose read data, but the supplied evidence does not establish a successful disclosure path. * No write, UAF, controlled reclaim, authorization bypass, LPE, or integrity modification is shown. * No additional availability point; the same invalid dereference is already counted as crash/DoS. 3. Reachability analysis The trigger requires configuring histogram and synthetic-event fields through tracefs. The evidence supports local, deterministic triggering once malicious configuration is accepted, but does not establish whether this requires host root, a particular capability, or delegated tracing access. No namespace-scoped complete trigger, remote path, prior setup details, special hardware, or race is shown. 4. Primitive and severity reading The primitive is attacker-influenced scalar-to-pointer semantic reinterpretation followed by a kernel dereference. It is neither a UAF nor an OOB write. The patch-supported effects are an invalid kernel read and plausible crash; disclosure remains unresolved because no read-back path is demonstrated. This is CLASS_A under the strong semantic-reinterpretation rule, requiring Important-class review despite uncertain privilege and absent write/LPE proof. Auto-downgrade is unsafe because validation accepted one semantic type while later consumers used it as an active kernel pointer. 5. One-sentence report phrase A malformed tracing histogram can cause an attacker-supplied 64-bit scalar to be dereferenced as a kernel stacktrace pointer, enabling a kernel crash and an unconfirmed disclosure possibility. 6. Manual review advice MANUAL CHECK REQUIRED Confirm tracefs privilege/delegation requirements and whether stacktrace processing can return pointed-to kernel data through tracing output. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields Commit: 1f36e4ddd05d540f363dbaa4c23042549f15b3ef Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1f36e4ddd05d540f363dbaa4c23042549f15b3ef Commit description: In check_synth_field(), when a synthetic event field is a stacktrace (field->is_stack) and the histogram field is not a "long[" stacktrace array, validation falls through to the generic size and signedness comparison. Because parse_synth_field() sets a stacktrace field's type to "__data_loc unsigned long[]", its size is sizeof(u64) and synth_field_signed() marks it as signed. Consequently, any 8-byte signed scalar histogram field passes the fallback check, and its scalar value is subsequently dereferenced as a kernel stacktrace pointer in get_field_size() and trace_stack(). Furthermore, checking strstr(hist_field->type, "long[") is insufficient because tracepoint fields defined with __bitmask() or __rel_bitmask() also have type "__data_loc unsigned long[]" or "__rel_loc unsigned long[]", whilst create_hist_field() treats them as 4-byte scalar values without HIST_FIELD_FL_STACKTRACE. Propagate HIST_FIELD_FL_STACKTRACE to variable references and field variables (whilst excluding variable aliases from per-element stacktrace capture), and reject any mismatch between HIST_FIELD_FL_STACKTRACE and field->is_stack in check_synth_field(). Cc: stable@vger.kernel.org Fixes: 00cf3d6 ("tracing: Allow synthetic events to pass around stacktraces") Link: https://patch.msgid.link/20261013112449.1006088-1-lee@kernel.org Signed-off-by: Lee Jones Acked-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman Changed files: kernel/trace/trace_events_hist.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=1f36e4ddd05d540f363dbaa4c23042549f15b3ef ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99163 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99163 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:L/PR:H/UI:N/S:U/C:L/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H The Best / paranoid CVSS score: 7.1 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: 5 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: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).