From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64523][MODERATE 7.0] net/handshake: Take a long-lived file reference at submit [ Upstream Date: Sat, 25 Jul 2026 14:38:13 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64523 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: 685b10dd0e32c7782cead16c8cf055c609678583 List-Id: CVE: CVE-2026-64523 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: net/handshake: Take a long-lived file reference at submit [ Upstream Commit: 685b10dd0e32c7782cead16c8cf055c609678583 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=685b10dd0e32c7782cead16c8cf055c609678583 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64523 Analysis date: Sat, 25 Jul 2026 14:38:13 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A race in net handshake can let the accept side use a request after the backing socket file has been released, creating a file or socket lifetime UAF risk that is most likely a local DoS but deserves manual review for possible higher impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64523 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64523 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-2026-64523 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 'A lifetime race in net handshake can leave the accept side with a request whose backing socket file has already been released. sock_hold keeps struct sock alive but does not keep struct socket or sock file alive, so a consumer that closes the last file reference while a handshake is pending can let sock_release tear down the socket before handshake_nl_accept_doit finishes preparing the accepted file descriptor. For the CVSS the PR:L is used for the paranoid score because a local unprivileged or reduced capability process may be able to trigger the relevant handshake consumer and close or cancel its socket while the handshake daemon is processing the request. The issue is not directly network reachable as a standalone packet path, although practical exposure depends on the protocol using net handshake and on whether remote traffic can cause pending handshakes. Impact is at least local denial of service via use after free or invalid socket lifetime, and worst case may allow confidentiality and integrity impact due to a real file or socket lifetime UAF, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES RACE ERRORPATH TEST 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: **Actionable Moderate at minimum** ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. A local process may be able to create or close the relevant consumer socket while a handshake request is pending, depending on the protocol using net handshake. * Memory corruption, weak or indirect corruption candidate: +1. The patch fixes a stale lifetime relationship where sock_hold keeps struct sock alive but not the owning struct socket or sock file. * Real lifetime corruption: +1. This is a real file or socket lifetime bug involving missing get_file and fput synchronization. * Reliable kernel crash or strong DoS: +1. A stale socket or file lifetime during accept side processing can plausibly lead to invalid dereference or kernel crash. * Hard or timing dependent race: -1. The vulnerable window is between handshake_req_next and FD_PREPARE or get_file, plus concurrent close or cancel activity. * Availability impact realistic: +1. If triggered, the effect is host kernel instability rather than a contained userspace failure. Paranoid delta: * Paranoid adds +1 for stronger manual review sensitivity around a real file or socket lifetime UAF in networking handshake infrastructure. This does not assume a proven LPE primitive, but keeps the issue out of auto close because stale socket file lifetime bugs can be under described in commit text. Not awarded: * No remote reachable +2. The affected path is not a standalone packet parsing path. * No strong LPE +2. The patch does not show attacker controlled reclaim, writable stale object access, callback control, type confusion, or arbitrary write. * No confidentiality or integrity impact in the conservative score. These remain theoretical without a concrete reuse or disclosure primitive. ## 3. Reachability analysis The most realistic trigger is local and race dependent. A process or service using a kernel protocol backed by net handshake may submit a handshake request and then close or cancel the socket while the accept side is processing the request. Namespaces or reduced capability service models may matter because the relevant socket consumer could be reachable from less than full host root in some deployments. This is not directly network reachable by arbitrary packets, although remote traffic may indirectly cause pending handshakes for protocols that use this infrastructure. The path is configuration and protocol dependent, not a universal default packet path. Call-site confidence: medium. The patch describes the concrete lifetime window and shows the file reference fix, but the exact external protocol call sites and deployment reachability are not included in the provided diff. ## 4. Severity interpretation This behaves above an ordinary Moderate because it is a real lifetime bug involving struct socket and sock file ownership, not just a warning or resource leak. Realistic impact is most likely local denial of service through a stale pointer or invalid lifetime during handshake accept processing. Theoretical impact could be higher because file and socket lifetime UAF bugs may become exploitable if object reuse is controllable, but the provided patch does not demonstrate reclaim control, arbitrary write, or a concrete privilege escalation chain. Therefore it is best treated as Actionable Moderate at minimum, with manual review required. ## 5. One-sentence report phrase A race in net handshake can let the accept side use a request after the backing socket file has been released, creating a file or socket lifetime UAF risk that is most likely a local DoS but deserves manual review for possible higher impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a race dependent real lifetime corruption bug involving socket and file references. Even though the conservative evidence supports DoS more strongly than LPE, the class is UAF adjacent and the patch explicitly fixes missing long lived ownership across asynchronous accept, completion, cancel, and error paths. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/handshake: Take a long-lived file reference at submit [ Upstream Commit: 685b10dd0e32c7782cead16c8cf055c609678583 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=685b10dd0e32c7782cead16c8cf055c609678583 Changed files: net/handshake/handshake.h net/handshake/netlink.c net/handshake/request.c net/sock.h 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=685b10dd0e32c7782cead16c8cf055c609678583 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64523 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64523 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).