From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63919][MODERATE 7.0] xfrm: input: hold netns during deferred transport reinjection [ Upstream Date: Sun, 19 Jul 2026 19:31:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63919 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 7ee59eda8820b758ed29e1cd3222359c7b97302c List-Id: CVE: CVE-2026-63919 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: xfrm: input: hold netns during deferred transport reinjection [ Upstream Commit: 7ee59eda8820b758ed29e1cd3222359c7b97302c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7ee59eda8820b758ed29e1cd3222359c7b97302c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63919 Analysis date: Sun, 19 Jul 2026 19:31:25 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A deferred XFRM transport reinjection path stored a `struct net` pointer without holding a netns reference, allowing namespace teardown before callback execution and creating a local race-dependent UAF candidate with likely DoS impact and possible higher impact requiring manual review. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63919 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63919 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 7.0 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-2026-63919 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Deferred XFRM transport reinjection stores a struct net pointer in skb cb and uses it later from xfrm_trans_reinject. Without holding a netns reference, the namespace can be torn down before the deferred callback runs, leaving a stale kernel pointer and creating a possible use after free condition. For the CVSS the PR:L is used because reliable triggering likely requires local code able to create or tear down network namespaces and exercise XFRM paths, which may be available to an unprivileged local user on systems with user namespaces enabled. The issue is not directly network reachable as a standalone remote attack because namespace lifetime control is local, although packet processing can be part of the trigger path. Impact is at least a local denial of service via kernel crash and in the paranoid case may allow confidentiality or integrity impact due to the UAF class, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) YES SIMPLEFIX SKB HARDWARE LINUS KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1 Likely reachable by local code that can create or tear down network namespaces and exercise XFRM/IPsec transport paths. On systems with unprivileged user namespaces enabled, this may be available without full host root. * Memory corruption, weak primitive: +1 The bug is a stale `struct net` pointer kept in `skb->cb` across deferred work. This is a UAF candidate, but no controlled reclaim, overwrite, type confusion, or arbitrary write is shown. * Real lifetime corruption: +1 The patch explicitly fixes a missing netns reference across async deferred reinjection work. * Reliable kernel crash / strong DoS: +1 A stale `struct net` used in the reinjection callback can plausibly crash the kernel. * XFRM packet-processing path exposure: +1 XFRM/IPsec is a networking packet-processing path. It is configuration-dependent, but should not be treated as a rare debug-only subsystem. * Hard race / teardown timing required: -1 Triggering requires a netns lifetime race against deferred reinjection. Paranoid adjustment: * Do not subtract the race point in the paranoid score because namespace teardown plus queued deferred work can be a realistic lifetime pattern under stress or crafted local workloads. No additional LPE bonus is awarded conservatively because the patch does not show attacker-controlled reclaim, object replacement, callback control, refcount takeover, or write-after-free. ## 3. Reachability analysis The bug is not directly remote-network exploitable as a standalone issue. Packet processing is part of the affected path, but the key condition is local control over namespace lifetime and XFRM transport reinjection timing. Typical reliable triggering likely requires local code with the ability to create or destroy network namespaces and configure or exercise XFRM/IPsec paths. In host configurations where unprivileged user namespaces are enabled, a local unprivileged user may obtain namespace-local capabilities sufficient to reach relevant networking setup paths. If user namespaces are disabled and XFRM setup requires host `CAP_NET_ADMIN`, practical reachability is significantly lower. The affected subsystem is not enabled in every deployment, but XFRM/IPsec is a real production networking feature, not a debug-only or rare hardware path. Call-site confidence: high. The provided patch shows both the queueing site and the deferred callback consuming the stored `struct net` pointer. ## 4. Severity interpretation This behaves above an ordinary Moderate because it is a real async lifetime bug in networking code and creates a plausible UAF condition on `struct net`. Realistic impact is most clearly local DoS through kernel crash. Theoretical impact could be higher because stale namespace pointers are security-sensitive kernel objects, but the patch does not demonstrate controlled reuse or a concrete privilege-escalation primitive. Therefore the conservative score stays borderline/manual-review, while the paranoid score reaches Actionable Moderate. This should not be auto-closed solely as a DoS cleanup. ## 5. One-sentence report phrase A deferred XFRM transport reinjection path stored a `struct net` pointer without holding a netns reference, allowing namespace teardown before callback execution and creating a local race-dependent UAF candidate with likely DoS impact and possible higher impact requiring manual review. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a real lifetime/UAF-class bug in a networking packet-processing path, with namespace-mediated local reachability and plausible but unproven impact beyond DoS. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: xfrm: input: hold netns during deferred transport reinjection [ Upstream Commit: 7ee59eda8820b758ed29e1cd3222359c7b97302c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7ee59eda8820b758ed29e1cd3222359c7b97302c Changed files: net/xfrm/xfrm_input.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=7ee59eda8820b758ed29e1cd3222359c7b97302c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63919 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63919 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:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 4 Paranoid ActionableScore: 5 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: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).