From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64558][IMPORTANT] s390/pkey: Check length in pkey_pckmo handler implementation Date: Wed, 29 Jul 2026 12:51:55 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64558 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 02028a24e26d85262ab9c8fc4344e1f3503007fc List-Id: CVE: CVE-2026-64558 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: s390/pkey: Check length in pkey_pckmo handler implementation Commit: 02028a24e26d85262ab9c8fc4344e1f3503007fc Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02028a24e26d85262ab9c8fc4344e1f3503007fc Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64558 Analysis date: Wed, 29 Jul 2026 12:51:55 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A missing protkey output length check in the s390 pkey_pckmo key_to_protkey handler can allow a local caller with pkey interface access to trigger a kernel out of bounds write during protected key generation, causing DoS and requiring manual review for possible privilege escalation impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64558 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64558 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-2026-64558 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-787;CWE-120;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'The pkey_pckmo key_to_protkey handler can copy t protkey into the caller supplied protkey buffer without checking whether t len fits in the provided protkeylen value. This is a local s390 pkey API issue and can become a kernel out of bounds write if the output buffer is smaller than the generated protected key. For the CVSS the PR:L is used for the paranoid score because a local user or process with access to the pkey interface may be able to trigger the vulnerable conversion path without full administrator privileges, depending on device permissions and deployment policy. The issue is not network reachable and requires local interaction with the pkey interface. Impact is at least local denial of service via kernel memory corruption and in worst case may allow confidentiality or integrity impact due to a kernel write primitive. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES SIMPLEFIX IMPROVEONLY LINUS YES NO guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. The affected handler is part of the s390 pkey API path, and a local process with access to the pkey interface may be able to request key_to_protkey conversion. * Constrained kernel buffer overwrite: +1. The bug is a missing output length check before memcpy into the caller supplied protkey buffer. * Weak LPE concern: +1. The primitive is a kernel out of bounds write, but the target and payload appear constrained and no reclaim or arbitrary write primitive is shown. * Reliable kernel crash / strong DoS: +1. A too small output buffer can plausibly corrupt adjacent kernel memory and crash the kernel. * Privileged kernel / crypto key-management corruption path: +1. The corruption occurs inside a trusted s390 protected-key conversion handler. * Rare architecture / configuration exposure: -1. This is s390-specific and depends on the pkey facility and interface availability. Paranoid additional interpretation: * Memory corruption, strong corruption primitive: +2 instead of constrained +1. The patch prevents an unchecked memcpy past the supplied kernel buffer. * Privilege escalation plausible: +2. A local kernel OOB write can be exploitable beyond DoS in the worst defensible case, although no practical exploit primitive is demonstrated. * Confidentiality impact plausible: +1. Kernel memory corruption can theoretically affect secrets or key-management state. * Integrity impact plausible: +1. Kernel memory corruption can theoretically alter adjacent kernel state. ## 3. Reachability analysis The issue is local, not network reachable. Triggering requires access to the s390 pkey conversion path, likely through the pkey userspace interface or an in-kernel caller reachable from that interface. If device permissions restrict pkey access to root or a privileged service, the practical score is closer to the conservative value. If ordinary local users or reduced-privilege service accounts can access the pkey interface, PR:L is the right practical interpretation. Namespaces and containers do not automatically make this reachable. However, reduced-capability service contexts should not be treated as full host-root if they can access the pkey device. The path is architecture and hardware dependent, so exposure is narrower than generic syscalls or common networking paths. Call-site confidence: medium. The patch directly shows the unsafe memcpy and the missing length check, but full callers and device permission policy are not included. ## 4. Severity interpretation This behaves like an actionable Moderate at minimum and a Strong Important candidate in the paranoid interpretation. The realistic demonstrated issue is a local kernel buffer overflow leading to memory corruption or crash. The theoretical escalation concern is based on a concrete OOB write primitive, but practical LPE depends on buffer placement, payload controllability, allocator context, and access to the pkey interface. This should not be auto-closed as an ordinary low-risk validation fix because the validation protects a memcpy destination size in kernel code. ## 5. One-sentence report phrase A missing protkey output length check in the s390 pkey_pckmo key_to_protkey handler can allow a local caller with pkey interface access to trigger a kernel out of bounds write during protected key generation, causing DoS and requiring manual review for possible privilege escalation impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. Reason: the patch fixes a concrete missing bounds check before memcpy in kernel code, making this a real memory corruption candidate rather than a pure validation or DoS-only issue. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: s390/pkey: Check length in pkey_pckmo handler implementation Commit: 02028a24e26d85262ab9c8fc4344e1f3503007fc Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02028a24e26d85262ab9c8fc4344e1f3503007fc Commit description: Explicitly check the length of the target buffer in the pkey_pckmo implementation of the key_to_protkey() handler function. The handler function fails, if the generated output data exceeds the length of the provided target buffer. Cc: stable@vger.kernel.org Fixes: 8fcc231 ("s390/pkey: Introduce pkey base with handler registry and handler modules") Reported-by: Christian Borntraeger Reviewed-by: Harald Freudenberger Signed-off-by: Holger Dengler Signed-off-by: Alexander Gordeev Signed-off-by: Greg Kroah-Hartman Changed files: drivers/s390/crypto/pkey_pckmo.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=02028a24e26d85262ab9c8fc4344e1f3503007fc ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64558 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64558 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:L/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: 5 Paranoid ActionableScore: 7 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: NO 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).