From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53091][IMPORTANT] net: pull headers in qdisc_pkt_len_segs_init() [ Upstream Date: Wed, 24 Jun 2026 15:14:35 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53091 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 9d4f5c68f5ad4ab425f3ce1500c97c9f9743999a List-Id: CVE: CVE-2026-53091 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: net: pull headers in qdisc_pkt_len_segs_init() [ Upstream Commit: 9d4f5c68f5ad4ab425f3ce1500c97c9f9743999a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d4f5c68f5ad4ab425f3ce1500c97c9f9743999a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53091 Analysis date: Wed, 24 Jun 2026 15:14:35 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: Malformed GSO skbs in the Linux networking transmit path could leave TCP or UDP headers outside skb head, allowing later TSO helpers to copy invalid memory and potentially cause a kernel crash or kernel memory disclosure in local or virtual-network trigger scenarios. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53091 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53091 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-2026-53091 IMPORTANT CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7.1';DESCR 'A malformed GSO skb can reach the transmit path with TCP or UDP headers not fully pulled into skb head. qdisc_pkt_len_segs_init previously inspected headers but did not guarantee that drivers and TSO helpers could later copy hdr_len bytes from skb data safely. This can lead to an out-of-bounds read in helpers such as tso_build_hdr, with possible kernel crash or leakage of kernel memory into generated transmit data. For the CVSS the PR:L is used for the paranoid score because reliable triggering normally requires a local process or a virtual network peer with the ability to feed crafted GSO skb state into the host TX path. The issue is not a normal Internet remote packet vector, but it can be adjacent in virtualized or trusted network environments where GSO metadata crosses a boundary. Impact is at least denial of service and in the paranoid interpretation may include confidentiality and integrity impact due to the out-of-bounds read primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) MAYBE REMOTE INIT SKB LINUS QDISC KPANIC PACKET KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - checked ====================================================================== 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 or low-privilege trigger: +1. A local process or virtual networking path may be able to feed crafted GSO skb state into the TX path. * Weak or indirect memory-safety primitive: +1. The patch prevents use of headers that were inspected but not pulled into skb head, with risk around later memcpy from skb data. * Reliable kernel crash / strong DoS: +1. Malformed GSO state can reach TSO helpers and cause invalid memory access or crash. * Confidentiality impact plausible: +1. An out-of-bounds read from skb linear data may leak kernel memory into generated transmit data. * Common networking core path: +1. The affected code is in net/core/dev.c and runs in the generic transmit/qdisc path. * Broad/default/common subsystem exposure: +1. GSO/TSO and qdisc transmit processing are common kernel networking features. * Hard or special triggering conditions: -1. The issue is not a normal Internet packet receive bug and likely requires crafted local or virtualized skb/GSO conditions. Paranoid additional signals: * Adjacent or virtual-network trigger treated as stronger exposure: +1. In virtualized or trusted network environments, a peer may influence GSO metadata across a boundary. * Local high-control kernel data-plane API: +1. Networking transmit paths can expose high-control skb construction through local sockets, tunnels, tap/vhost, or similar data-plane mechanisms. ## 3. Reachability analysis This is not a conventional remote Internet packet parsing bug. Ordinary packets received from the wire do not normally carry attacker-controlled GSO metadata into the host TX path. Realistic triggering is more likely from a local process, containerized networking setup, tap/vhost/virtio-like boundary, tunnel path, or another internal producer of malformed GSO skbs. Namespace and container behavior matters. If untrusted workloads can create or influence virtual network devices, tunnels, or high-control transmit paths, the practical privilege requirement may be closer to local low privilege than full host root. If only trusted root or CAP_NET_ADMIN can create the relevant skb state, the conservative score is more appropriate. ## 4. Severity interpretation This is above ordinary Moderate because the affected code is in the core networking transmit path and the patch addresses a memory-safety condition around GSO headers not being pulled into skb head before later TSO copying. The strongest realistic impact is DoS, but a confidentiality concern is plausible because the dangerous operation is an out-of-bounds read-like copy from skb data into generated transmit headers. The evidence does not support arbitrary write or direct code execution. The paranoid score is justified by networking-core exposure, virtual boundary concerns, and possible kernel memory disclosure, not by a proven LPE primitive. ## 5. One-sentence report phrase Malformed GSO skbs in the Linux networking transmit path could leave TCP or UDP headers outside skb head, allowing later TSO helpers to copy invalid memory and potentially cause a kernel crash or kernel memory disclosure in local or virtual-network trigger scenarios. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the bug is in a common networking core TX path and has a plausible memory-safety primitive with possible information disclosure, while the exact reachability depends on skb producers such as local sockets, tunnels, tap/vhost, virtio, or container networking. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: pull headers in qdisc_pkt_len_segs_init() [ Upstream Commit: 9d4f5c68f5ad4ab425f3ce1500c97c9f9743999a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d4f5c68f5ad4ab425f3ce1500c97c9f9743999a Changed files: net/core/tso.c include/net/dropreason-core.h net/core/dev.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=9d4f5c68f5ad4ab425f3ce1500c97c9f9743999a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53091 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53091 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:H The Best / paranoid CVSS vector: AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.1 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: YES 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).