From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99078][IMPORTANT] net/mlx5e: Prevent stale XSK buffer release on MPWQE refill retry [ Upstream Date: Mon, 26 Oct 2026 15:17:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99078 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: f3a52e2ec2788a7f6b64137985c087188a54ad4f List-Id: CVE: CVE-2026-99078 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: net/mlx5e: Prevent stale XSK buffer release on MPWQE refill retry [ Upstream Commit: f3a52e2ec2788a7f6b64137985c087188a54ad4f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f3a52e2ec2788a7f6b64137985c087188a54ad4f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99078 Analysis date: Mon, 26 Oct 2026 15:17:26 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: An AF_XDP refill retry can double-free an XSK frame through a stale pointer after pool return and possible reallocation, corrupting active buffer ownership. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99078 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99078 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-2026-99078 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-99078 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT IMPORTANT AEGIS_AS=4 LEGACY=IMPORTANT RESULT=SAME (final reconciliation agrees; DECISION: both IMPORTANT) 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-415;*CWE-416;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'This is a stale ownership and double release memory safety bug in the mlx5e AF_XDP zero copy receive path. An MPWQE refill failure can leave released slots marked as releasable, allowing a later NAPI retry to call xsk_buff_free again through stale pointers after the frames have returned to the XSK pool and may have been reallocated. For the CVSS the PR:L value is selected because an attacker normally needs local access to create and operate an AF_XDP socket and configure the affected receive path. AC:H reflects the required allocation failure and refill retry state. Availability impact includes kernel failure or receive path corruption. Reuse of an already released frame provides a plausible confidentiality and integrity risk, but arbitrary write and reliable privilege escalation are not demonstrated. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 6 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 3.4 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) MAYBE REMOTE ERRORPATH NETWORK LINUS KPANIC_UNSUPPORTED_REMOVED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 5. * Conservative score: 5; REAL UAF FLOOR 5 applies but does not alter the score. * Raw paranoid score: 6. * Paranoid score: 6; no cap or additional floor applied. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 Real UAF/lifetime violation: `xsk_buff_free()` releases XSK frames, but stale pointers remain releasable and are passed to `xsk_buff_free()` again on a later NAPI refill retry. * +1 Concrete repeated release: the first free can return the frame to the XSK pool; the same slot and stale pointer survive because `actual_wq_head` is not advanced; retry performs another ownership-ending free. * +1 Reliable crash/strong DoS concern: double release of a reallocated XSK frame can corrupt pool/descriptor state and plausibly cause invalid descriptors, WQE errors, warnings, or kernel failure. * +1 Attacker-influenced repeated lifetime sequence: an AF_XDP workload can repeatedly exercise refill and allocation-failure retries; the pressure test reached over 1.5 million failures. * Paranoid +1: the second free can operate after the frame has been reallocated, creating a technically defensible active-buffer ownership-corruption path beyond a shallow stale dereference. * FLOOR 5 applies because the exact stale reference receives a second non-idempotent lifetime/ownership mutation after the first release may have ended its ownership lifetime. * No arbitrary write, controlled target, callback control, disclosure, LPE, or C/I impact is demonstrated. No extra availability point is awarded for the same possible crash. * NEW52 B5-R does not apply: no retry-accumulated heap OOB write is shown. 3. Reachability analysis The trigger requires AF_XDP zero-copy on an mlx5e striding receive queue, refill allocation failure, and a later NAPI retry. Local AF_XDP traffic and memory pressure can influence retries, but the supplied evidence does not establish who can complete socket creation, XDP attachment, device/RQ configuration, and zero-copy operation. It therefore does not prove either ordinary unprivileged or host-admin-only reachability. Capability namespace scope and prior privileged setup remain unresolved. The retry is reproducible under pressure rather than shown to require a narrow one-shot race, so no timing penalty applies. A compatible mlx5 device is required, but it is not established as rare or physical-attacker-only. 4. Primitive and severity reading This is an active XSK buffer ownership UAF/double release, not fixed stale storage. It is category B: a second lifetime/ownership mutation through a stale pointer, potentially after the frame has been reallocated. The shown effects are stale release and pool/descriptor corruption; stronger memory corruption, host compromise, or privilege escalation remain unproven. ImportantCandidate=YES because the concrete repeated release affects potentially reallocated active buffers and leaves material post-lifetime corruption leverage unresolved. AutoDowngradeAllowed=NO because treating it as cleanup-only DoS would discard that ownership-corruption chain. CLASS_A is not justified without controlled replacement contents, directed write, or a demonstrated exploitation effect. 5. One-sentence report phrase An AF_XDP refill retry can double-free an XSK frame through a stale pointer after pool return and possible reallocation, corrupting active buffer ownership. 6. Manual review advice MANUAL CHECK REQUIRED Confirm complete AF_XDP privilege requirements and whether stale release of a reallocated frame yields exploitable pool or descriptor corruption beyond denial of service. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/mlx5e: Prevent stale XSK buffer release on MPWQE refill retry [ Upstream Commit: f3a52e2ec2788a7f6b64137985c087188a54ad4f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f3a52e2ec2788a7f6b64137985c087188a54ad4f Changed files: drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c net/xdp_sock_drv.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=f3a52e2ec2788a7f6b64137985c087188a54ad4f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99078 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99078 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:L/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: 5 Paranoid ActionableScore: 6 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: NO 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).