From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53370][LOW] perf/x86/intel: Improve validation and configuration of ACR masks Date: Sun, 19 Jul 2026 05:57:03 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53370 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: aab56b95bee3ff79176b13443cd9d7cfe9747df0 List-Id: CVE: CVE-2026-53370 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: perf/x86/intel: Improve validation and configuration of ACR masks Commit: aab56b95bee3ff79176b13443cd9d7cfe9747df0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aab56b95bee3ff79176b13443cd9d7cfe9747df0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53370 Analysis date: Sun, 19 Jul 2026 05:57:03 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: Intel PMU ACR mask validation could allow a local perf user to supply invalid ACR mask state or retain stale hardware mask bits, causing incorrect ACR event programming and unreliable perf sampling results without evidence of memory corruption or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53370 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53370 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-2026-53370 LOW CHECK WITH IMPACT FROM ORIG NN LOW 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:L/A:L';*CWE-20;CWE-665;CWE-682;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'Intel PMU ACR mask handling can accept or retain invalid configuration state from attr.config2 and stale hw.config1 values. This can cause incorrect ACR event programming, skipped configuration of later ACR groups, or unreliable perf sampling results for the affected event group. For the CVSS the PR:L is used for the paranoid score because a local user or process with access to perf_event_open can supply attr.config2 and request ACR events. The issue is local only and is not network reachable. Impact is mainly low integrity impact on performance monitoring data, with at most low availability impact for the affected perf event configuration. There is no supported path to memory corruption or privilege escalation from this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-53370 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: ec980e4facef8110f6fce27e5b6344660117f01f YES NO NO unknown MAYBE OOB HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 A local process with access to `perf_event_open` and the relevant Intel PMU ACR events can influence `attr.config2`. * Integrity impact plausible: +1 Invalid or stale ACR masks can cause incorrect PMU event programming, skipped ACR group configuration, or unreliable perf sampling results. Not triggered: * No memory corruption signal. The patch fixes validation and state clearing for PMU masks, but does not show UAF, OOB write, double free, type confusion, arbitrary write, or stale pointer reuse. * No privilege escalation signal. There is no concrete primitive that affects credentials, memory ownership, callbacks, refcounts, or kernel object lifetime. * No reliable kernel crash signal. The described impact is misconfiguration and incorrect sampling, not panic or system-wide DoS. * No remote reachability. This is a local perf/PMU configuration path. * No high-control API bonus. `perf_event_open` exposes kernel objects, but this patch does not show exploitation-relevant control over memory layout, object lifetime, callbacks, or references. ## 3. Reachability analysis The likely trigger is a local user or process that can create Intel PMU ACR perf events and provide a crafted `attr.config2` mask. In typical hardened deployments, access to raw PMU events may be restricted by `perf_event_paranoid`, `CAP_PERFMON`, or `CAP_SYS_ADMIN`, but the practical CVSS-style interpretation can still be PR:L where perf access is delegated or available to local users. Namespaces and containers may matter only if perf access is delegated into the container. This does not appear to be a default network-facing path. The affected feature is also Intel ACR-specific, so exposure is narrower than core perf functionality. Call-site confidence: high. The relevant changed function and its direct behavior are present in the patch. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like correctness/security-hardening issue rather than an Important kernel vulnerability. The realistic impact is incorrect performance monitoring configuration or unreliable sampling data. Theoretical escalation is not supported by the patch context because there is no memory corruption, lifetime bug, write primitive, or security-boundary bypass. ## 5. One-sentence report phrase Intel PMU ACR mask validation could allow a local perf user to supply invalid ACR mask state or retain stale hardware mask bits, causing incorrect ACR event programming and unreliable perf sampling results without evidence of memory corruption or privilege escalation. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED The issue is validation/configuration-only, local, non-network reachable, and does not show a concrete memory corruption or privilege escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: perf/x86/intel: Improve validation and configuration of ACR masks Commit: aab56b95bee3ff79176b13443cd9d7cfe9747df0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aab56b95bee3ff79176b13443cd9d7cfe9747df0 Commit description: Currently there are several issues on the user space ACR mask validation and configuration. - The validation for user space ACR mask (attr.config2) is incomplete, e.g., the ACR mask could include the index which belongs to another ACR events group, but it's not validated. - An early return on an invalid ACR mask caused all subsequent ACR groups to be skipped. - The stale hardware ACR mask (hw.config1) is not cleared before setting new hardware ACR mask. The following changes address all of the above issues. - Figure out the event index group of an ACR group. Any bits in the user-space mask not present in the index group are now dropped. - Instead of an early return on invalid bits, drop only the invalid portions and continue iterating through all ACR events to ensure full configuration. - Explicitly clear the stale hardware ACR mask for each event prior to writing the new configuration. Besides, a non-leader event member of ACR group could be disabled in theory. This could cause bit-shifting errors in the acr_mask of remaining group members. But since ACR sampling requires all events to be active, this should not be a big concern in real use case. Add a "FIXME" comment to notice this risk. Fixes: ec980e4 ("perf/x86/intel: Support auto counter reload") Signed-off-by: Dapeng Mi Signed-off-by: Peter Zijlstra (Intel) Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260430002558.712334-2-dapeng1.mi@linux.intel.com Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/events/intel/core.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=aab56b95bee3ff79176b13443cd9d7cfe9747df0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53370 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53370 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:L/UI:N/S:U/C:N/I:L/A:N The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 4.4 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: 2 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).