From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74436][MODERATE 7.0] rxrpc: serialize kernel accept preallocation with socket teardown [ Upstream Date: Sat, 15 Aug 2026 03:39:48 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74436 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: 0337cdba0c477f176c0459bed012109453184573 List-Id: CVE: CVE-2026-74436 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: rxrpc: serialize kernel accept preallocation with socket teardown [ Upstream Commit: 0337cdba0c477f176c0459bed012109453184573 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0337cdba0c477f176c0459bed012109453184573 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74436 Analysis date: Sat, 15 Aug 2026 03:39:48 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A race in `rxrpc_kernel_charge_accept()` can allow a preallocation path to use a freed `rxrpc_backlog` after concurrent socket teardown, causing at least kernel crash risk and requiring manual review for possible memory corruption impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74436 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74436 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-2026-74436 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE 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-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'rxrpc_kernel_charge_accept read rx backlog without socket or backlog synchronization while concurrent teardown could clear rx backlog and free the backlog rings. A preallocation worker could then keep using a freed rxrpc_backlog object while updating backlog head and tail fields and array slots, which makes this a use after free candidate rather than a pure crash only bug. For the CVSS the PR:L is used because reliable triggering likely requires a local or delegated actor able to influence rxrpc service socket teardown or kernel service lifecycle, while network traffic may help hit the race. The issue is not proven to be directly network reachable as a standalone remote attack, but rxrpc is a network protocol and incoming service traffic can be part of the vulnerable timing window. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES DANGER INIT UAF LOG IMPROVEONLY LINUS KPANIC 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 * Local unprivileged or delegated trigger: +1 Reliable triggering likely requires a local or delegated actor that can influence an RxRPC service socket lifecycle or kernel service using RxRPC. * Memory corruption, strong corruption primitive: +2 The patch describes use of a freed `struct rxrpc_backlog` after concurrent teardown. The stale object is not only read, it may be updated through backlog head and tail fields and array slots. * Real lifetime corruption: +1 This is a real lifetime race between `rxrpc_kernel_charge_accept()` and `rxrpc_discard_prealloc()`, where teardown can free backlog rings while another path still uses the pointer. * Reliable kernel crash / strong DoS: +1 Use-after-free in kernel networking state can realistically crash the kernel. * Hard or unreliable race / special timing required: -1 The issue depends on a concurrent preallocation worker and socket teardown window. * Rare or narrower subsystem exposure: -1 for conservative score only RxRPC is not a broad default packet path like TCP, UDP, netfilter, or core skb receive processing. Exposure depends on RxRPC or AFS-style service usage. * Weak LPE concern: +1 for paranoid score only The stale object is writable after free, so manual review should consider whether allocator reuse can turn this into a stronger primitive. No controlled reclaim or callback control is demonstrated in the patch. ## 3. Reachability analysis The bug is not proven to be a standalone remote network attack. RxRPC is a network protocol, and incoming traffic can contribute to backlog/preallocation activity, but the race also requires teardown or disabling of the service backlog. In typical deployments, reliable triggering likely needs local influence over an RxRPC service socket, an in-kernel RxRPC service, or a delegated service lifecycle. Namespaces and containers may matter if a reduced-privilege service or containerized workload can create or control the relevant RxRPC socket lifecycle. This should not be treated as full host-root-only without checking the product configuration. The path is not a broad default networking path, but it is kernel networking code and the patch clearly describes a freed object being reused. Call-site confidence: medium. The changed function and direct stale pointer use are visible, but full service lifecycle callers are not included in the supplied patch. ## 4. Severity interpretation This is stronger than an ordinary Moderate crash because the patch describes a real UAF on `struct rxrpc_backlog` with writes into freed backlog state. However, the realistic exploitation evidence remains limited because the race is timing-dependent and no attacker-controlled reclaim, type confusion, callback dispatch, or arbitrary write primitive is shown. Conservatively this is borderline/manual-review Moderate. Paranoid handling makes it an Actionable Moderate because kernel lifetime corruption in networking code has enough risk to avoid auto-closure. ## 5. One-sentence report phrase A race in `rxrpc_kernel_charge_accept()` can allow a preallocation path to use a freed `rxrpc_backlog` after concurrent socket teardown, causing at least kernel crash risk and requiring manual review for possible memory corruption impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch describes a real race-based use-after-free with writable stale object access in kernel networking state. No proven LPE primitive is shown, but the lifetime corruption is concrete enough that this should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: rxrpc: serialize kernel accept preallocation with socket teardown [ Upstream Commit: 0337cdba0c477f176c0459bed012109453184573 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0337cdba0c477f176c0459bed012109453184573 Changed files: net/rxrpc/call_accept.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=0337cdba0c477f176c0459bed012109453184573 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74436 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74436 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).