From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98375][MODERATE REGULAR] xen/netfront: drop RX packets with a short Ethernet header handle_incoming_queue() pulls pull_to bytes into the head before calling eth_type_trans(). pull_to is the length of the first RX slot, capped at RX_COPY_THRESHOLD, and that length comes from the backend. Nothing checks it against ETH_HLEN. If the first slot is shorter than ETH_HLEN and more slots follow, the head ends up shorter than an Ethernet header while skb->len is longer, and eth_type_trans() BUG()s in __skb_pull(). If the whole packet is shorter than ETH_HLEN, eth_type_trans() reads the header past the end of the data instead. Pull at least ETH_HLEN, and drop the packet if that fails, which also drops packets too short to hold an Ethernet header. This also checks the return value of the pull, which was ignored. Fixes: 0d16021 ("xen: add virtual network device driver") Cc: stable@vger.kernel.org Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261007-b4-xen-netfront-short-head-v1-1-12d7113a7e4e@toxicpanda.com Signed-off-by: Jakub Kicinski Date: Fri, 09 Oct 2026 22:05:22 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98375 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 089e58805c452e52179482b1025a8e309a57f801 List-Id: CVE: CVE-2026-98375 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: xen/netfront: drop RX packets with a short Ethernet header handle_incoming_queue() pulls pull_to bytes into the head before calling eth_type_trans(). pull_to is the length of the first RX slot, capped at RX_COPY_THRESHOLD, and that length comes from the backend. Nothing checks it against ETH_HLEN. If the first slot is shorter than ETH_HLEN and more slots follow, the head ends up shorter than an Ethernet header while skb->len is longer, and eth_type_trans() BUG()s in __skb_pull(). If the whole packet is shorter than ETH_HLEN, eth_type_trans() reads the header past the end of the data instead. Pull at least ETH_HLEN, and drop the packet if that fails, which also drops packets too short to hold an Ethernet header. This also checks the return value of the pull, which was ignored. Fixes: 0d16021 ("xen: add virtual network device driver") Cc: stable@vger.kernel.org Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261007-b4-xen-netfront-short-head-v1-1-12d7113a7e4e@toxicpanda.com Signed-off-by: Jakub Kicinski Commit: 089e58805c452e52179482b1025a8e309a57f801 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=089e58805c452e52179482b1025a8e309a57f801 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98375 Analysis date: Fri, 09 Oct 2026 22:05:22 -0400 ActionableScore: 1 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98375 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98375 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-2026-98375 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98375 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-252;Other CVSS 'AV:A/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.8';DESCR 'A Xen network backend can provide an RX packet whose first slot is shorter than ETH_HLEN while additional slots make the total skb length appear valid. The netfront receive path can then call eth_type_trans with an insufficient linear Ethernet header which can trigger a BUG in __skb_pull and crash the guest kernel. A packet whose total length is shorter than ETH_HLEN can instead cause an out of bounds read past the valid skb data. For the CVSS the PR:L value is used for the paranoid score because a reduced privilege driver domain or backend service may control the shared RX ring without having unrestricted host root privileges. The base assessment uses PR:H for conventional Xen deployments where backend control normally requires dom0 level access. This issue is adjacent rather than ordinarily Internet reachable because the attacker must control or compromise the Xen network backend. Impact is at least denial of service against the guest and the out of bounds read justifies limited confidentiality and integrity impact for manual review in the paranoid assessment.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE SIMPLEFIX NETWORK SKB HARDWARE PACKET DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=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: 1 * Paranoid score: 1 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown Positive signals: * +1 Reliable kernel crash / strong DoS. A backend-controlled short first RX slot followed by additional fragments can leave the linear head shorter than ETH_HLEN. The subsequent `eth_type_trans()` call can trigger `BUG()` through `__skb_pull()`. * +0 Limited OOB read. If the entire packet is shorter than ETH_HLEN, `eth_type_trans()` reads beyond valid skb data. No disclosure path, subsequent write, or security-sensitive value influence is established. Negative signals: * No negative points. Backend privilege is unresolved, so no host-admin penalty is applied. * No race penalty. The malformed slot layout provides a deterministic trigger after backend control is obtained. * No niche-subsystem or hardware penalty. Xen deployment is a prerequisite, but no unusual physical hardware is required. Important non-awarded signals: * Direct remote reachability is not established. Ordinary network traffic is not shown to control Xen RX slot boundaries without backend cooperation. * Local unprivileged reachability is not established. * No UAF, stale lifetime operation, controlled reclaim, OOB write, arbitrary write, or callback influence exists. * Confidentiality is not awarded because the internal OOB read is not shown to reach userspace, the backend, or another observable output. * Integrity is not awarded because no write or persistent state modification is demonstrated. * No extra Availability point is awarded because it would double-count the same kernel crash. * B5-R is not established because there is no heap OOB write, retry-accumulated index, or later consumption of corrupted written state. * B3-PENDING is not established because there is no write to shared or file-backed storage. * B4-PENDING is not established because no authorization decision or mandatory security guard is bypassed. 3. Reachability analysis The immediate input is controlled by a Xen network backend through the length and arrangement of RX slots. A malicious or compromised backend can construct the short first slot required for the crash or OOB-read paths. The supplied evidence does not establish whether the complete attacker is conventional dom0 with host-administrator powers or a reduced-privilege driver domain or backend service. Therefore `HostAdminRequired=UNKNOWN`. Numeric host UID 0 is likewise unresolved. The operation is not namespace-capability based, and an attacker-created user or network namespace does not provide control over the Xen backend ring. No prior sysctl, boot option, or special physical hardware is identified beyond running the guest with Xen netfront and an associated backend. External Ethernet traffic alone is not shown to preserve attacker-selected malformed RX slot geometry through the backend. The trigger is deterministic rather than a race once backend control is available. 4. Primitive and severity interpretation The first demonstrated behavior is an invalid skb layout followed by a `BUG()` when `eth_type_trans()` attempts to consume an Ethernet header from an insufficient linear head. This is a strong guest availability failure. The second behavior is a read beyond the valid skb packet data when the complete packet is shorter than ETH_HLEN. It is a limited read-only OOB primitive with no established disclosure or subsequent corruption sink. There is no stale storage, active structured-object UAF, repeated release, refcount mutation, or lifetime violation. There is also no authorization bypass or shared-backing ownership violation. The issue is therefore `CLASS_C`. The demonstrated consequence is guest kernel crash or invalid internal read. Stronger confidentiality, integrity, privilege-escalation, or cross-domain corruption consequences remain unsupported. `ImportantCandidate=NO` because no independently useful corruption or boundary-bypass primitive remains after excluding the crash. `AutoDowngradeAllowed=YES` because this is a constrained crash/OOB-read case without unresolved write or lifetime leverage. Operational severity is ordinary Moderate and depends on control or compromise of the Xen backend. 5. One-sentence report phrase A malicious or compromised Xen network backend can provide an RX packet with an undersized Ethernet header and trigger a guest kernel BUG or a limited out-of-bounds read, but no disclosure, write primitive, or privilege escalation is established. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Confirm the product-specific Xen backend privilege boundary and whether any deployed backend can be controlled below host-administrator privilege, but the supplied patch does not preserve an Important-grade primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: xen/netfront: drop RX packets with a short Ethernet header handle_incoming_queue() pulls pull_to bytes into the head before calling eth_type_trans(). pull_to is the length of the first RX slot, capped at RX_COPY_THRESHOLD, and that length comes from the backend. Nothing checks it against ETH_HLEN. If the first slot is shorter than ETH_HLEN and more slots follow, the head ends up shorter than an Ethernet header while skb->len is longer, and eth_type_trans() BUG()s in __skb_pull(). If the whole packet is shorter than ETH_HLEN, eth_type_trans() reads the header past the end of the data instead. Pull at least ETH_HLEN, and drop the packet if that fails, which also drops packets too short to hold an Ethernet header. This also checks the return value of the pull, which was ignored. Fixes: 0d16021 ("xen: add virtual network device driver") Cc: stable@vger.kernel.org Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261007-b4-xen-netfront-short-head-v1-1-12d7113a7e4e@toxicpanda.com Signed-off-by: Jakub Kicinski Commit: 089e58805c452e52179482b1025a8e309a57f801 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=089e58805c452e52179482b1025a8e309a57f801 Changed files: drivers/net/xen-netfront.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=089e58805c452e52179482b1025a8e309a57f801 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98375 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98375 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:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 6.8 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: unknown Paranoid ActionableScore: 1 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).