From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74406][MODERATE REGULAR] vxlan: Fix potential null-ptr-deref in vxlan_gro_prepare_receive(). [ Upstream Date: Sat, 15 Aug 2026 07:07:10 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74406 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: 4 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 9c58c729d32e7cea5772cc44929c6cd61e5a31cd List-Id: CVE: CVE-2026-74406 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: vxlan: Fix potential null-ptr-deref in vxlan_gro_prepare_receive(). [ Upstream Commit: 9c58c729d32e7cea5772cc44929c6cd61e5a31cd Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9c58c729d32e7cea5772cc44929c6cd61e5a31cd Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74406 Analysis date: Sat, 15 Aug 2026 07:07:10 -0400 ActionableScore: 4 ActionableScore lower bound: 2 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A race in the VXLAN GRO receive path can leave `sk_user_data` NULL while packets are being processed, allowing a reachable VXLAN sender to contribute to a timing-dependent kernel NULL pointer dereference and denial of service during tunnel teardown. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74406 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74406 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74406 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-362;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'A race in the VXLAN/GRO receive path can leave sk_user_data as NULL while vxlan_gro_prepare_receive() is processing a packet. If udp_tunnel_sock_release() clears the socket user data concurrently, the receive path may dereference a missing vxlan_sock state and crash the kernel. For the CVSS the PR:N is used for the paranoid score because a remote sender may not need an account on the target when the VXLAN UDP endpoint is reachable and the tunnel is being torn down concurrently. The attack complexity is high because the crash depends on a narrow race with socket release. Impact is denial of service through kernel crash, with no concrete evidence of information disclosure or privilege escalation from the shown patch. VXLAN is usually deployed in data center or overlay networks rather than exposed to the public Internet, so practical exploitation normally requires reachability to the overlay or trusted internal network.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) YES NULLPTR SIMPLEFIX NETWORK INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Paranoid score signals: * Remote reachable / network-triggerable: +2. VXLAN is a UDP based overlay protocol and the affected function is in the receive GRO path. A remote sender that can reach the VXLAN endpoint may contribute packets during the teardown race. * Reliable kernel crash / strong DoS: +1. The patch fixes a potential NULL pointer dereference in `vxlan_gro_prepare_receive()`, which can crash the kernel. * Common networking packet-processing path: +1. The bug is in a network receive path for VXLAN GRO processing. * Broad/common deployed exposure: +1. VXLAN is common in data center and overlay networking deployments, though not usually exposed to the public Internet. * Hard or unreliable race / special timing required: -1. Triggering requires overlap between packet receive processing and `udp_tunnel_sock_release()` clearing `sk_user_data`. Conservative score does not fully count remote triggerability because reliable exploitation appears to require a concurrent tunnel/socket teardown event that is usually controlled by local network administration. No memory corruption or LPE signals are awarded. The patch supports NULL dereference DoS, not UAF reclaim, stale object reuse, overwrite, type confusion, or privilege escalation. ## 3. Reachability analysis The affected path is reachable through VXLAN packet reception when UDP socket GRO is used. A remote attacker may be able to send VXLAN traffic if they have access to the overlay or internal network where the VXLAN endpoint is exposed. However, the crash depends on a race with `udp_tunnel_sock_release()`, so the attacker may not be able to trigger it reliably unless tunnel teardown occurs concurrently. Local reliable setup or teardown generally requires `CAP_NET_ADMIN`. Containers or delegated network namespaces could reduce the practical privilege barrier if untrusted workloads can create or destroy VXLAN devices, but this is not the default assumption for host networking. VXLAN is not normally Internet-facing, but it is common in data center and virtualized networking environments. ## 4. Severity interpretation This behaves more like a borderline actionable Moderate than an Important-class vulnerability. The realistic impact is kernel crash / DoS. Theoretical escalation is not supported by the shown patch because the fixed condition is a NULL check after `sk_user_data` may become NULL, with no evidence of writable stale object access or attacker-controlled memory reuse. The main reason not to auto-close is that the bug is in a network packet-processing path and can potentially be influenced remotely in VXLAN deployments, even though the race makes exploitation unreliable. ## 5. One-sentence report phrase A race in the VXLAN GRO receive path can leave `sk_user_data` NULL while packets are being processed, allowing a reachable VXLAN sender to contribute to a timing-dependent kernel NULL pointer dereference and denial of service during tunnel teardown. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Network reachable packet-processing races with kernel crash impact should be reviewed manually, even when the demonstrated primitive is only NULL pointer dereference and the race appears difficult to trigger reliably. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vxlan: Fix potential null-ptr-deref in vxlan_gro_prepare_receive(). [ Upstream Commit: 9c58c729d32e7cea5772cc44929c6cd61e5a31cd Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9c58c729d32e7cea5772cc44929c6cd61e5a31cd Changed files: drivers/net/vxlan/vxlan_core.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=9c58c729d32e7cea5772cc44929c6cd61e5a31cd ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74406 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74406 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:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.9 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: 4 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).