From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80602][MODERATE REGULAR] perf/x86/amd/lbr: Fix kernel address leakage Date: Fri, 28 Aug 2026 04:37:55 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80602 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: 3 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 5be478c1e08981ca91b34de310d7e2638171d9d8 List-Id: CVE: CVE-2026-80602 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: perf/x86/amd/lbr: Fix kernel address leakage Commit: 5be478c1e08981ca91b34de310d7e2638171d9d8 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5be478c1e08981ca91b34de310d7e2638171d9d8 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80602 Analysis date: Fri, 28 Aug 2026 04:37:55 -0400 ActionableScore: 3 ActionableScore lower bound: unknown Actionable bucket: Borderline, manual review recommended / Low to Moderate information leak Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80602 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80602 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-2026-80602 MODERATE 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:H/I:N/A:N';*CWE-200;CWE-497;CWE-203;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'AMD LBR v2 branch filtering can expose kernel branch source addresses to user space when a user only branch stack is requested through perf. The hardware filter checks the privilege level of the branch target, so SYSRET or ERET records may still contain kernel from addresses and disclose kernel pointers. This is a local information disclosure issue and can weaken KASLR or other address hiding assumptions. For the CVSS the PR:L is selected because a local user or process must be able to use perf branch sampling through the local perf interface. The issue is not network reachable. Impact is confidentiality only, with no direct integrity or availability impact from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended / Low to Moderate information leak (with actual score 3) YES OOB LEAK HARDWARE INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 1. ActionableScore * Conservative score: 3 * Paranoid score: 3 * Final recommended bucket: **Borderline, manual review recommended / Low to Moderate information leak** 2. Signal breakdown * Local unprivileged trigger: +1. A local user or process with access to perf branch sampling can request a user-only branch stack. * Confidentiality impact plausible: +1. Kernel branch source addresses can be exposed to user space, weakening KASLR and kernel address hiding. * Broad/default/common subsystem exposure: +1. perf is a common Linux facility, although actual reachability depends on perf_event_paranoid policy and AMD LBR v2 hardware support. * No memory corruption: +0. The patch only filters reported LBR entries and does not show UAF, OOB access, overwrite, refcount misuse, or type confusion. * No integrity or availability impact: +0. The described effect is address disclosure only, with no crash or write primitive. 3. Reachability analysis The bug is locally reachable through perf branch-stack sampling on AMD processors with X86_FEATURE_AMD_LBR_V2. It is not network reachable. In typical hardened deployments, unprivileged perf access may be restricted by perf_event_paranoid or admin policy, which lowers practical exposure. Containers and namespaces do not automatically make this reachable unless the container has access to perf events and the relevant PMU functionality. 4. Severity interpretation This behaves like a local information disclosure issue rather than memory corruption or LPE. The leaked kernel addresses can weaken KASLR and may assist another exploit, but the patch does not support direct privilege escalation, arbitrary read, arbitrary write, or DoS. This is above a trivial cleanup because it crosses the intended user/kernel sampling boundary, but it is not an Important-class vulnerability by itself. 5. One-sentence report phrase A local perf user on AMD LBR v2 systems can receive kernel branch source addresses in a user-only branch stack, causing kernel pointer disclosure that may weaken KASLR but does not directly provide integrity or availability impact. 6. Manual review recommendation MANUAL CHECK RECOMMENDED. Kernel address disclosure can affect exploit mitigations and should be checked against product perf access defaults, but there is no supported memory corruption or direct privilege escalation primitive here. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: perf/x86/amd/lbr: Fix kernel address leakage Commit: 5be478c1e08981ca91b34de310d7e2638171d9d8 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5be478c1e08981ca91b34de310d7e2638171d9d8 Commit description: A user-only branch stack can contain branches that originate from the kernel. As a result, kernel addresses are exposed to user space even when PERF_SAMPLE_BRANCH_USER is requested. On AMD processors supporting X86_FEATURE_AMD_LBR_V2, perf can still report SYSRET/ERET entries for which the branch-from addresses are in the kernel. E.g. $ perf record -e cycles -o - -j any,save_type,u -- \ perf bench syscall basic --loop 1000 | \ perf script -i - -F brstack|tr ' ' '\n'| \ grep -E '0x[89a-f][0-9a-f]{15}' ... 0xffffffff81001268/0x717a90a38f1a/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH 0xffffffff81001268/0x717a90a39157/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH 0xffffffff81001268/0x717a90a2c628/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH 0xffffffff81001268/0x717a90a41b60/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH 0xffffffff81001268/0x717a90a260db/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH 0xffffffff81001268/0x717a90a260db/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH 0xffffffff81001268/0x717a8bef1c30/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH 0xffffffff81001268/0x717a8e4d3c90/M/-/-/0/ERET/NON_SPEC_CORRECT_PATH ... The reason is that the hardware filter only considers the privilege level applicable to the branch target. Extend software filtering to also validate the branch-from addresses against br_sel, so that any branch record whose branch-from address is in the kernel is dropped when PERF_SAMPLE_BRANCH_USER is requested. Fixes: f4f925d ("perf/x86/amd/lbr: Add LbrExtV2 hardware branch filter support") Reported-by: Ian Rogers Signed-off-by: Sandipan Das Signed-off-by: Ingo Molnar Cc: stable@vger.kernel.org Cc: Peter Zijlstra Link: https://patch.msgid.link/a898a29725f6b2f30518354cdc2e432db66c43cf.1783680119.git.sandipan.das@amd.com Signed-off-by: Greg Kroah-Hartman Changed files: arch/x86/events/amd/lbr.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=5be478c1e08981ca91b34de310d7e2638171d9d8 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80602 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80602 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:L/I:N/A:N The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N The Best / paranoid CVSS score: 5.5 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: 3 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).