From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74515][LOW] KVM: s390: pci: Reject adapter interrupt forwarding if already enabled Date: Sat, 15 Aug 2026 18:50:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74515 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: 78d9648e7e960546d5b72504a0b0358cd8bb1e9d List-Id: CVE: CVE-2026-74515 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: KVM: s390: pci: Reject adapter interrupt forwarding if already enabled Commit: 78d9648e7e960546d5b72504a0b0358cd8bb1e9d Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=78d9648e7e960546d5b72504a0b0358cd8bb1e9d Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74515 Analysis date: Sat, 15 Aug 2026 18:50:26 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: KVM s390 zPCI adapter interrupt forwarding could be enabled multiple times for the same device, overwriting existing forwarding state and leaking host resources, with local KVM device-management access required and denial of service as the expected impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74515 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74515 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: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74515 LOW CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-772;**CWE-400;CWE-404;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'KVM s390 zPCI adapter interrupt forwarding could be enabled more than once for the same device even though the underlying MPCIFC flow requires unregister before another register operation. Repeated enable requests can overwrite the stored forwarding state and leak host resources associated with the previous registration. For the CVSS the PR:L is used because a local user or service with access to KVM device management can trigger the ioctl path, while full host root is not always a required practical assumption in KVM deployments. The issue is not network reachable and is triggered through the local KVM control plane rather than guest packet or storage traffic. Impact is denial of service through resource leakage, with no concrete evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES VIRT SIMPLEFIX LEAK HARDWARE LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like** ## 2. Signal breakdown Triggered signals: * Local privileged or delegated KVM trigger: +1 The issue is reached through a KVM s390 zPCI control path, likely via an ioctl or VM device-management operation. * Availability impact realistic: +1 in paranoid scoring Repeated enable requests can overwrite existing AIF state and leak host resources, so sustained abuse may cause resource exhaustion. * Rare and configuration-dependent subsystem: -1 in conservative scoring This requires s390 KVM with zPCI adapter interrupt forwarding, which is not a broad default Linux exposure. Not triggered: * Remote reachable: +0 No network or guest packet path is shown. * Firmware-mediated external influence: +0 The trigger is a local KVM control-plane request, not firmware-fed input. * Generic memory corruption: +0 The patch describes overwritten registration state and leaked resources, not UAF, OOB write, double free, type confusion, or arbitrary write. * Privilege escalation plausible: +0 No concrete LPE primitive is supported by the patch. * Strong DoS: +0 conservative, weakly +1 only in paranoid availability interpretation Resource exhaustion is plausible through repeated calls, but no immediate crash or panic path is demonstrated. Call-site confidence: medium. The patch shows the guarded function and the state check, but not the full ioctl call path or exact privilege checks. ## 3. Reachability analysis The likely attacker is a local user, VM management process, or service account with access to KVM s390 zPCI device-management operations. In typical deployments this is not exposed to arbitrary remote users and is not reachable through packet traffic. Namespaces or containers may matter if KVM device access is delegated to a reduced-privilege service or container root. In that case PR:L is more practical than PR:H, but the attacker still needs access to a specialized KVM device-management path. The affected configuration is not common across all Linux systems. It requires s390 KVM and zPCI adapter interrupt forwarding. Realistic exploitation is mainly repeated ioctl abuse causing host resource leakage, not memory corruption or privilege escalation. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like resource-leak issue rather than an Important-class kernel vulnerability. The main impact is local denial of service through leaked adapter interrupt forwarding resources. Theoretical concern is limited to state overwrite and resource leakage. Realistic exploitation evidence does not show UAF, stale callback, type confusion, attacker-controlled reclaim, arbitrary write, or cross-boundary data corruption. ## 5. One-sentence report phrase KVM s390 zPCI adapter interrupt forwarding could be enabled multiple times for the same device, overwriting existing forwarding state and leaking host resources, with local KVM device-management access required and denial of service as the expected impact. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This can be auto-closed for default triage because it is a local, configuration-specific KVM resource leak without a demonstrated memory corruption or privilege-escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: KVM: s390: pci: Reject adapter interrupt forwarding if already enabled Commit: 78d9648e7e960546d5b72504a0b0358cd8bb1e9d Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=78d9648e7e960546d5b72504a0b0358cd8bb1e9d Commit description: The MPCIFC instruction doesn't allow registering adapter interrupts without first unregistering. So reject any request to enable interrupt forwarding if its already enabled for the zPCI device. This also fixes overwriting and thus leaking resources when the ioctl is called multiple times for the same device. Fixes: 3c5a1b6 ("KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding") Cc: stable@vger.kernel.org Reviewed-by: Christian Borntraeger Reviewed-by: Matthew Rosato Signed-off-by: Farhan Ali Tested-by: Matthew Rosato Signed-off-by: Christian Borntraeger Signed-off-by: Greg Kroah-Hartman Changed files: arch/s390/kvm/pci.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=78d9648e7e960546d5b72504a0b0358cd8bb1e9d ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74515 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74515 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:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).