From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72025][MODERATE 7.0] s390/monwriter: Reject buffer reuse with different data length Date: Sat, 15 Aug 2026 08:22:36 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72025 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: 7 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 096dff1247037d329c04b3a5be0ecdfb1c5c7ac6 List-Id: CVE: CVE-2026-72025 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: s390/monwriter: Reject buffer reuse with different data length Commit: 096dff1247037d329c04b3a5be0ecdfb1c5c7ac6 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=096dff1247037d329c04b3a5be0ecdfb1c5c7ac6 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72025 Analysis date: Sat, 15 Aug 2026 08:22:36 -0400 ActionableScore: 7 ActionableScore lower bound: 2 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: s390 monwriter could reuse a kernel data buffer while accepting a later record with a different datalen, allowing a local user with device access to trigger an out-of-bounds user copy into kernel memory and potentially cause crash or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72025 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72025 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-2026-72025 MODERATE 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-122;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 's390 monwriter can reuse an existing data buffer while accepting a later record with a different data length. The first record determines the kernel buffer size, so a malicious user with access to the monwriter misc device can change the later datalen and cause an out-of-bounds user copy into the kernel buffer. This is a local kernel memory corruption issue and can cause at least a denial of service through crash. In the worst case it may allow confidentiality or integrity impact and privilege escalation because the corrupted object is in kernel memory. For the CVSS the PR:L is used for the paranoid score because default permissions are root only, but practical deployments may delegate device access or relax permissions for monitoring tools. The issue is not network reachable and requires local access to the s390 monwriter device.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) YES WRITE OOB DANGER SIMPLEFIX HARDWARE LINUS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Memory corruption, Strong corruption primitive: +2. The commit explicitly states that changing datalen on reused buffers can cause out of bounds user copy into a kernel buffer and memory corruption. * Reliable kernel crash / strong DoS: +1. Kernel heap corruption can realistically lead to crash. * Requires admin/root/CAP_* in typical deployments: -2. The monwriter misc device is root-only by default. * Rare AND difficult-to-reach subsystem/configuration: -1. This is s390-specific monwriter functionality, not a broad default Linux attack surface. Conservative total: 2. Paranoid signals: * Local unprivileged trigger: +1. Applied only for the paranoid case where monwriter device permissions are relaxed or delegated to a monitoring service account. * Memory corruption, Strong corruption primitive: +2. User-controlled datalen mismatch can drive an out of bounds copy into a kernel buffer. * Privilege escalation plausible: +2. This is kernel heap memory corruption with attacker-influenced input, so LPE is technically plausible even if not demonstrated. * Reliable kernel crash / strong DoS: +1. Crash is a realistic minimum impact. * Confidentiality impact plausible: +1. Kernel memory corruption can potentially expose or influence sensitive kernel state in worst case. * Integrity impact plausible: +1. Kernel memory corruption can potentially modify adjacent kernel objects. * Rare AND difficult-to-reach subsystem/configuration: -1. s390 monwriter is specialized and not broadly exposed. Paranoid total: 7. ## 3. Reachability analysis The bug requires local access to the s390 monwriter misc device. In typical deployments the device is created with root-only permissions, so the conservative trigger requires administrative access and practical exposure is low. Namespaces and containers do not automatically make this reachable. However, if a container, service account, or monitoring tool is granted access to the device node without full host-root equivalence, the practical PR can drop to a lower-privileged local attacker model. The issue is not network reachable. Call-site confidence: medium. The patch context and commit message clearly describe the copy-size invariant and downstream OOB user copy, but the full copy call path is not included in the supplied diff. ## 4. Severity interpretation This is not an ordinary validation-only bug. The validation fix prevents a concrete kernel out-of-bounds write condition caused by inconsistent buffer reuse state. Realistically, default root-only permissions reduce exposure and make the conservative severity low to moderate. Paranoid triage should not auto-close it because the primitive is kernel memory corruption and delegated device access could convert the issue into a local privilege escalation candidate. ## 5. One-sentence report phrase s390 monwriter could reuse a kernel data buffer while accepting a later record with a different datalen, allowing a local user with device access to trigger an out-of-bounds user copy into kernel memory and potentially cause crash or privilege escalation. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. Reason: the bug is explicit kernel memory corruption with attacker-influenced length, and although default permissions are root-only, delegated or relaxed monwriter device access could make it an actionable local privilege escalation candidate. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: s390/monwriter: Reject buffer reuse with different data length Commit: 096dff1247037d329c04b3a5be0ecdfb1c5c7ac6 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=096dff1247037d329c04b3a5be0ecdfb1c5c7ac6 Commit description: When data buffers are reused, e.g. for interval sample records, the first record determines the data length, and the size of the buffer for user copy. Current monwriter code does not check if the data length was changed for subsequent records, which also would never happen for valid user programs. However, a malicious user could change the data length, resulting in out of bounds user copy to the kernel buffer, and memory corruption. By default, the monwriter misc device is created with root-only permissions, so practical impact is typically low. Fix this by checking for changed data length and rejecting such records. Cc: stable@vger.kernel.org Signed-off-by: Gerald Schaefer Reviewed-by: Christian Borntraeger Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman Changed files: drivers/s390/char/monwriter.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=096dff1247037d329c04b3a5be0ecdfb1c5c7ac6 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72025 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72025 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: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: 2 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: 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).