From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98724][MODERATE REGULAR] nvmet: pci-epf: reject too-short SGL segments Date: Mon, 19 Oct 2026 00:50:59 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98724 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: 2423a05dd0f21330c47ce0ae1cb54a8b0be821e2 List-Id: CVE: CVE-2026-98724 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: nvmet: pci-epf: reject too-short SGL segments Commit: 2423a05dd0f21330c47ce0ae1cb54a8b0be821e2 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2423a05dd0f21330c47ce0ae1cb54a8b0be821e2 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98724 Analysis date: Mon, 19 Oct 2026 00:50:59 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A PCI host can provide a too-short NVMe SGL segment that makes `nvmet_pci_epf_get_sgl_segment()` read before a heap allocation and potentially panic a hardened endpoint kernel, but no OOB write, disclosure, or privilege-escalation primitive is established. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98724 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98724 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98724 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98724 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;CWE-129;*CWE-20;CWE-191;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.6';DESCR 'Bug class: out of bounds read caused by missing input length validation and integer index underflow. Exploit primitive: one byte OOB read with a conditional 16 byte OOB copy into internal kernel state. No OOB write, UAF, arbitrary write, or direct information disclosure to the host is established. The abbreviated commit ID and supplied patch text do not provide a stable public link or assigned CVE. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7.6 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE READ KASAN OOB NVME LINUS TEST INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO ## 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 2 * Paranoid score: 2 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: ## 2. Signal breakdown Conservative signals: * +1 Weak or indirect corruption candidate. A host-controlled short length makes `nr_descs` zero and causes an indexed read from `sgls[-1]`. The value can also be interpreted as a segment descriptor and copied into valid internal storage. * +0 Reliable kernel crash. The OOB read reproduced consistently, but the supplied panic requires KASAN with `panic_on_warn`. A production-kernel panic is not established. * +0 Confidentiality. No path returning the preceding slab bytes to the PCI host is shown. * +0 Integrity. The internal descriptor copy is concerning, but subsequent security-relevant consumption is not established. * +0 Direct network reachability. This requires an NVMe PCI endpoint relationship rather than ordinary network traffic. * +0 Privilege penalty. The privileges needed to submit the malformed command from the controlling PCI host are unresolved, so no unsupported host-admin penalty is applied. Paranoid difference: * +1 Strong DoS concern. The invalid access was reproduced in 3 of 3 KASAN boots, and a malformed host-provided SGL deterministically reaches the vulnerable index. A fatal fault on hardened or diagnostic deployments is technically defensible. Important non-awarded signals: * No OOB write, UAF, arbitrary write, controlled reclaim, disclosure path, or privilege escalation is established. * NEW52 B5-R does not apply. There is no retry-accumulated index and no confirmed OOB write. * V33 does not apply. Although bytes can be copied into an internal descriptor, the supplied context does not establish later privileged consumption across a concrete trust boundary. * B3-PENDING does not apply because no shared-backing write exists. * Authorization bypass and B4-PENDING do not apply. * No additional Availability point is awarded for the same KASAN panic. ## 3. Reachability analysis The NVMe PCI host controls the SGL segment length and can provide a nonzero value smaller than one descriptor. The vulnerable system must expose an `nvmet` PCI endpoint target, which implies prior administrative provisioning and suitable PCI endpoint hardware. The supplied evidence does not establish whether an ordinary process on the controlling host can construct the malformed command or whether raw NVMe command submission requires elevated privileges. Therefore `HostAdminRequired=UNKNOWN`. Linux namespace capabilities are not relevant to the demonstrated PCI endpoint path, so `NamespaceScopedPrivilege=NO`. There is no timing race or retry requirement. Once malformed SGL input reaches this function, the index underflow is deterministic. ## 4. Primitive and severity interpretation The exact primitive is a slab OOB read caused by an index underflow: `nr_descs == 0` leads to access through `sgls[-1]`. The initial access reads one byte before the allocation. If that byte resembles a segment descriptor type, 16 preceding bytes are copied into valid internal descriptor storage and a negative descriptor count is returned. This is not an OOB write. The available context does not show that the copied descriptor is subsequently trusted for another memory operation, disclosed to the host, or used to cross a security boundary. The demonstrated consequence is a KASAN-detected invalid read and panic with `panic_on_warn`. A production crash is plausible but not proven. The issue is therefore `CLASS_C`, not Class A or Class B. `ImportantCandidate=NO` because no independently useful corruption or boundary-crossing primitive is established. `AutoDowngradeAllowed=YES` because the current evidence supports an invalid-read and DoS issue rather than unresolved Important-grade corruption. Manual review remains recommended to inspect callers for consumption of the copied descriptor and negative count. ## 5. One-sentence report phrase A PCI host can provide a too-short NVMe SGL segment that makes `nvmet_pci_epf_get_sgl_segment()` read before a heap allocation and potentially panic a hardened endpoint kernel, but no OOB write, disclosure, or privilege-escalation primitive is established. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Review callers to determine whether the copied pre-buffer descriptor or negative descriptor count can reach additional parsing, transfer, or DMA operations before being rejected. ## 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nvmet: pci-epf: reject too-short SGL segments Commit: 2423a05dd0f21330c47ce0ae1cb54a8b0be821e2 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2423a05dd0f21330c47ce0ae1cb54a8b0be821e2 Commit description: The host controls an SGL segment's length. A nonzero length smaller than one SGL descriptor makes nr_descs zero, so nvmet_pci_epf_get_sgl_segment() reads the type byte of sgls[-1] outside the allocated buffer. If that byte contains a segment descriptor type, the function also copies the preceding 16 bytes and returns a negative descriptor count. The read was reproduced in 3/3 KASAN boots with only the host transfer mocked by a KUnit test: BUG: KASAN: slab-out-of-bounds in nvmet_pci_epf_get_sgl_segment Read of size 1 by task kunit_try_catch Call Trace: nvmet_pci_epf_get_sgl_segment nvmet_pci_epf_short_sgl_test Kernel panic - not syncing: KASAN: panic_on_warn set ... Reject segments that cannot hold one descriptor before allocating or transferring their contents. Fixes: 0faa0fe ("nvmet: New NVMe PCI endpoint function target driver") Cc: stable@vger.kernel.org Assisted-by: LLM Reviewed-by: Christoph Hellwig Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> Signed-off-by: Keith Busch Signed-off-by: Greg Kroah-Hartman Changed files: drivers/nvme/target/pci-epf.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=2423a05dd0f21330c47ce0ae1cb54a8b0be821e2 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98724 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98724 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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 7.6 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).