From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74466][MODERATE REGULAR] s390/zcrypt: Close speculative mem read possibility Date: Sat, 15 Aug 2026 14:23:30 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74466 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: 2 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: 82b62eda68abfb7a33ac40f24b8c4128c2891148 List-Id: CVE: CVE-2026-74466 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: s390/zcrypt: Close speculative mem read possibility Commit: 82b62eda68abfb7a33ac40f24b8c4128c2891148 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82b62eda68abfb7a33ac40f24b8c4128c2891148 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74466 Analysis date: Sat, 15 Aug 2026 14:23:30 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate / not Actionable Moderate, manual review recommended for confidentiality side-channel Manual review required: YES Summary: A local s390 zcrypt ioctl path used a user-controlled domain value as an index after bounds checking but without a speculation barrier, allowing a possible Spectre style confidentiality leak under custom device and administrative CPRB conditions. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74466 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74466 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-2026-74466 MODERATE CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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:N/A:N';CWE-203;CWE-125;CWE-129;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'An s390 zcrypt ioctl path uses a user controlled domain value as an index into the custom device admin permission bitmap after a bounds check but without a speculation barrier. Under branch misprediction, the CPU may transiently use an out of range domain and speculatively read permission bitmap or adjacent memory through test_bit_inv, creating a Spectre style information disclosure risk. For the CVSS the PR:L is used because reliable triggering requires local code with access to the zcrypt device node and the ability to submit the relevant CCA or EP11 administrative CPRB path, but full root privileges are not necessarily required when a custom device node is delegated. The issue is not network reachable and does not provide a write primitive or direct privilege escalation. Impact is confidentiality only, with base C:L and paranoid C:H due to possible speculative kernel memory disclosure under special s390 zcrypt configurations.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / not Actionable Moderate, manual review recommended for confidentiality side-channel (with actual score 2) YES OOB SIMPLEFIX SPECTRE HARDWARE LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / not Actionable Moderate, manual review recommended for confidentiality side-channel** ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 Applies in the paranoid interpretation because a local process with access to the relevant zcrypt custom device node may submit the CCA or EP11 ioctl path. This does not require full host root if the device node is delegated. * Confidentiality impact plausible: +1 The missing `array_index_nospec()` creates a Spectre V1 style speculative read possibility from `perms->adm` or adjacent memory after a bounds check on a user-controlled `domain` value. Subtracting / limiting factors: * Rare AND difficult-to-reach subsystem/configuration: -1 in conservative score The issue is limited to s390 zcrypt, custom device nodes, administrative CPRB handling, and speculative execution conditions. This is not a broad default Linux attack surface. Not awarded: * Remote reachable: +0 No network path is shown. * Generic memory corruption: +0 This is not UAF, OOB write, double free, type confusion, or refcount corruption. * Privilege escalation plausible: +0 No write primitive, object corruption, callback control, or reclaim primitive is present. * Reliable kernel crash / strong DoS: +0 The patch prevents speculative information disclosure, not a crash path. ## 3. Reachability analysis The bug is reachable through local ioctl handling in `drivers/s390/crypto/zcrypt_api.c`. The attacker needs access to a zcrypt device node and the ability to submit the relevant CCA or EP11 CPRB path. In typical deployments this is restricted and architecture-specific, but custom device nodes may delegate access to non-root users or service accounts. Namespaces and containers do not automatically make this reachable unless the zcrypt device node is passed through or exposed. The affected path is not network reachable. Realistic exploitation also depends on s390 hardware, zcrypt configuration, administrative CPRB filtering, and whether a usable speculative side channel exists in practice. ## 4. Severity interpretation This behaves like an ordinary Moderate speculative information disclosure issue, not an Important-class kernel memory corruption vulnerability. The theoretical worst case is local confidentiality impact through transient execution, possibly higher than a permission bitmap leak if adjacent sensitive kernel memory can be inferred. Realistic exploitation evidence is limited by the specialized subsystem, local device access requirement, and side-channel complexity. It should not be auto-classified as Low because the affected code is crypto permission handling and the patch explicitly adds a Spectre mitigation for a user-controlled index. It also should not be treated as Important because there is no supported privilege escalation, write primitive, crash primitive, or broad remote exposure. ## 5. One-sentence report phrase A local s390 zcrypt ioctl path used a user-controlled domain value as an index after bounds checking but without a speculation barrier, allowing a possible Spectre style confidentiality leak under custom device and administrative CPRB conditions. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because this is an architecture-specific speculative execution information leak in crypto permission handling. However, the practical score remains low because there is no memory corruption, no DoS, no network reachability, and no demonstrated privilege escalation path. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: s390/zcrypt: Close speculative mem read possibility Commit: 82b62eda68abfb7a33ac40f24b8c4128c2891148 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82b62eda68abfb7a33ac40f24b8c4128c2891148 Commit description: The domain value is extracted from a given CCA or EP11 ioctl struct when a CPRB is about to be sent. Thus this is a user controlled value. Under some special conditions (custom device node used, administrative load) this value is used as an array index after bounds checking, but without speculation barrier. Add the missing array_index_nospec() call to prevent speculative execution where this domain value is used. Fixes: cfd68b3 ("s390/zcrypt: Filter admin CPRBs on custom devices") Cc: stable@vger.kernel.org Reported-by: Christian Borntraeger Reviewed-by: Finn Callies Signed-off-by: Harald Freudenberger Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman Changed files: drivers/s390/crypto/zcrypt_api.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=82b62eda68abfb7a33ac40f24b8c4128c2891148 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74466 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74466 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:L/UI:N/S:U/C:L/I:N/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N The Best / paranoid CVSS score: 4.7 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: 1 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: 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).