From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53095][IMPORTANT] bpf: Fix abuse of kprobe_write_ctx via freplace [ Upstream Date: Wed, 24 Jun 2026 15:44:18 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53095 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 8 X-AL-KERNEL-ActionableScore-Lower: 7 X-AL-KERNEL-Commit: b312cf41b9e43f442613053f6cad39898e1baf96 List-Id: CVE: CVE-2026-53095 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: bpf: Fix abuse of kprobe_write_ctx via freplace [ Upstream Commit: b312cf41b9e43f442613053f6cad39898e1baf96 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b312cf41b9e43f442613053f6cad39898e1baf96 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53095 Analysis date: Wed, 24 Jun 2026 15:44:18 -0400 ActionableScore: 8 ActionableScore lower bound: 7 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A BPF freplace program could bypass the intended kprobe_write_ctx restriction and modify pt_regs for kprobe target kernel functions, allowing local privileged or delegated BPF users to alter kernel function arguments with plausible DoS or privilege escalation impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53095 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53095 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: IMPORTANT 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-2026-53095 IMPORTANT CHECK 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:H/A:H';CWE-284;CWE-269;CWE-693;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A BPF freplace program could abuse a kprobe_write_ctx mismatch and attach to a kprobe target that was not allowed to write struct pt_regs. When the target kernel function runs, the freplace program can modify pt_regs and change register arguments of that kernel function, giving the BPF program unintended control over kernel execution state. For the CVSS the PR:L value is used in the paranoid score because exploitation requires local ability to load and attach tracing or extension BPF programs, often via delegated CAP_BPF CAP_PERFMON or similar service privileges rather than full root in practical deployments. The issue is not network reachable. Impact may include kernel logic corruption, denial of service, and plausible local privilege escalation because attacker controlled register changes can affect privileged kernel code paths.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) MAYBE INIT BPF LINUS KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=7 ## 1. ActionableScore * Conservative score: 7 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Privilege escalation plausible: +2 The bug allows a BPF freplace program to modify `struct pt_regs` for a kprobe target kernel function, effectively changing kernel function arguments at runtime. This is a plausible LPE class even without a classic UAF or OOB write. * Security-boundary bypass with practical sensitive-object access: +2 The patch enforces an intended BPF attach-time boundary around `kprobe_write_ctx`. Without it, a program with writeable uprobe-style context semantics can be attached in a way that affects kprobe execution on kernel functions. * Local high-control kernel data-plane API: +1 BPF tracing and freplace are high-control local kernel instrumentation APIs. * Reliable kernel crash / strong DoS: +1 Modifying register arguments of arbitrary probed kernel functions can plausibly crash the kernel or corrupt kernel control flow assumptions. * Integrity impact plausible: +1 Attacker-controlled modification of kernel function arguments can change privileged kernel behavior. * Confidentiality impact plausible: +1 If register modification affects security checks or object selection, sensitive data exposure is plausible, although not directly demonstrated. * Broad/common subsystem exposure: +1 BPF tracing is a common kernel facility on many production systems, even though access is usually restricted. * Requires CAP_BPF/CAP_PERFMON/CAP_SYS_ADMIN-like privileges in typical deployments: -1 conservative / 0 paranoid Conservative scoring applies a partial privilege penalty because BPF tracing access is normally restricted. The full -2 is not applied because this is a capability-boundary bypass and reduced-capability root, service accounts, or delegated BPF permissions are realistic deployment models. ## 3. Reachability analysis The bug is locally reachable by a user or service able to load and attach BPF tracing or freplace programs. It is not network reachable. In typical hardened deployments this requires `CAP_BPF`, `CAP_PERFMON`, or `CAP_SYS_ADMIN`, and unprivileged BPF is commonly disabled. However, container root, service accounts, observability agents, or delegated BPF permissions may reduce the practical privilege barrier below full host root. The vulnerable path is not a rare driver path. It is part of the BPF tracing attach logic. ## 4. Severity interpretation This behaves more like an Important candidate than an ordinary Moderate. The issue is not generic heap memory corruption, UAF, or OOB write, but it gives unintended control over `pt_regs` for kernel function execution. That is a strong kernel execution-state manipulation primitive and can plausibly lead to DoS, security-check bypass, or local privilege escalation depending on the chosen kprobe target. Realistic exploitation still depends on BPF privileges and target selection, so the conservative score is slightly lower than the paranoid score. ## 5. One-sentence report phrase A BPF freplace program could bypass the intended kprobe_write_ctx restriction and modify pt_regs for kprobe target kernel functions, allowing local privileged or delegated BPF users to alter kernel function arguments with plausible DoS or privilege escalation impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This should not be auto-closed because the primitive is not merely a warning or crash. It is unauthorized kernel register/context modification through BPF attach logic, with plausible integrity impact and local privilege escalation potential. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Fix abuse of kprobe_write_ctx via freplace [ Upstream Commit: b312cf41b9e43f442613053f6cad39898e1baf96 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b312cf41b9e43f442613053f6cad39898e1baf96 Changed files: kernel/bpf/syscall.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=b312cf41b9e43f442613053f6cad39898e1baf96 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53095 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53095 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:H/I:H/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 7 Paranoid ActionableScore: 8 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).