From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53156][MODERATE 7.0] nvmem: core: fix use-after-free bugs in error paths Date: Thu, 25 Jun 2026 05:06:21 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53156 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7 List-Id: CVE: CVE-2026-53156 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: nvmem: core: fix use-after-free bugs in error paths Commit: e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53156 Analysis date: Thu, 25 Jun 2026 05:06:21 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: The nvmem core error paths could drop the final reference to an nvmem device and then continue using the freed object, creating a local kernel use-after-free that is most likely a crash risk but deserves manual review for possible memory corruption impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53156 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53156 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-2026-53156 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'nvmem core has use after free error paths because __nvmem_device_put can drop the last reference and free the nvmem object while the same code path still reads nvmem layout or calls nvmem_layout_module_put with that pointer. A local trigger would normally need to drive nvmem consumer lookup or cell release error paths, for example through driver probe, device removal, module handling, or other platform management paths that reach of_nvmem_cell_get or nvmem_cell_put. For the CVSS the PR:L is used for the paranoid score because some systems may expose device management or probe paths to a reduced capability root, container root, service account, or delegated local management context rather than full host administrator control. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in worst case may allow confidentiality or integrity impact because the bug class is explicit use after free in kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES NVME ERRORPATH UAF HARDWARE LINUS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown * Memory corruption, strong corruption primitive: +2. The patch explicitly fixes use-after-free paths where `__nvmem_device_put()` may free `nvmem`, after which the same pointer was still used. * Real lifetime corruption: +1. This is a reference/lifetime ordering bug involving a possible final put followed by later object access. * Reliable kernel crash / strong DoS: +1. A freed `nvmem` object being dereferenced or passed to `nvmem_layout_module_put()` can plausibly crash the kernel. * Privileged kernel/device-management memory corruption path: +1. The bug is in nvmem core device-management and cell lifecycle handling. * Corruption primitive highly constrained or metadata-only: -1. The patch does not show attacker-controlled reclaim, object replacement, write-after-free, callback dispatch, or arbitrary write. * Requires admin/root/device-management in typical deployments: conservative -2. Typical triggering likely requires driver probe/remove, module/device lifecycle manipulation, or platform-device paths. * Paranoid reachability adjustment: +1 instead of full admin penalty. Some systems may expose relevant probe or device-management paths to reduced-capability root, container root, service accounts, or delegated local management contexts. Not counted: * Remote reachable: +0. No network path is shown. * Strong LPE plausibility: +0. UAF exists, but no reclaim, overwrite, stale callback, type confusion, or refcount takeover is demonstrated. * Confidentiality / integrity impact: +0 for the main score. They are theoretically possible for UAF class, but not supported by a concrete primitive in this patch. ## 3. Reachability analysis The realistic trigger is local and likely tied to nvmem consumer lookup, cell creation failure, cell release, driver probe, device removal, module handling, or platform management paths that reach `of_nvmem_cell_get()` or `nvmem_cell_put()`. In ordinary deployments this is not a direct unprivileged syscall-style attack surface and may require administrator-level device control. Namespaces or containers can matter if device management, module loading, sysfs/configuration access, or service-level probe actions are delegated to less-than-full-root contexts. The path is not network reachable and does not appear default-exposed to arbitrary local users on a normal system. ## 4. Severity interpretation This is not an ordinary cleanup bug because the fixed behavior is an explicit use-after-free in kernel memory. However, the demonstrated primitive is constrained: the patch shows use-after-put on an error path, but does not show attacker-controlled reuse, write-after-free, function pointer control, or a direct LPE chain. Realistically it behaves like a local DoS or constrained kernel-memory lifetime bug. Paranoid handling should keep it as Actionable Moderate because explicit UAF bugs are unsafe to auto-close without manual review. ## 5. One-sentence report phrase The nvmem core error paths could drop the final reference to an nvmem device and then continue using the freed object, creating a local kernel use-after-free that is most likely a crash risk but deserves manual review for possible memory corruption impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Explicit kernel use-after-free is present, even though the current patch does not demonstrate a practical privilege-escalation primitive. This should not be auto-closed without checking realistic triggerability on affected platforms and whether delegated device-management paths can make the bug reachable below full host-root privileges. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nvmem: core: fix use-after-free bugs in error paths Commit: e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7 Commit description: Fix several instances of error paths in which we call __nvmem_device_put() - which may end up freeing the underlying memory and other resources - and then keep on using the nvmem structure. Always put the reference to the nvmem device as the last step before returning the error code. Cc: stable@vger.kernel.org Fixes: 7ae6478 ("nvmem: core: rework nvmem cell instance creation") Fixes: e888d44 ("nvmem: resolve cells from DT at registration time") Signed-off-by: Bartosz Golaszewski Signed-off-by: Srinivas Kandagatla Link: https://patch.msgid.link/20260530204340.116743-3-srini@kernel.org Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman Changed files: drivers/nvmem/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=e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53156 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53156 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:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 3 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: NO 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).