From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45998][IMPORTANT] rxrpc: Fix potential UAF after skb_unshare() failure [ Upstream Date: Wed, 27 May 2026 17:29:03 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45998 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: e3bf143b1e98fb3d6d9e6825bcd683974d478e8c List-Id: CVE: CVE-2026-45998 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: rxrpc: Fix potential UAF after skb_unshare() failure [ Upstream Commit: e3bf143b1e98fb3d6d9e6825bcd683974d478e8c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3bf143b1e98fb3d6d9e6825bcd683974d478e8c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45998 Analysis date: Wed, 27 May 2026 17:29:03 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45998 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45998 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-2026-45998 IMPORTANT CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;**CWE-476;CWE-703;CWE-755;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'rxrpc_input_packet() could try to unshare a secure DATA skb early in the receive path. If skb_unshare() failed due to ENOMEM, the parent skb pointer could be cleared or the original skb could be consumed while rxrpc_io_thread() still expected to trace and free it, causing a NULL dereference or UAF-like crash. For the CVSS the PR:N is used because no local privileges are required on the victim when an RXRPC endpoint is reachable. The issue is network reachable in RXRPC deployments, but reliable triggering depends on allocation failure or memory pressure and therefore has AC:H. Impact is primarily denial of service, with limited confidentiality and integrity concern kept only for the paranoid score because the bug involves skb lifetime handling in a network receive path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) MAYBE INIT TRACE UAF SKB LINUS PACKET KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: 2. Signal breakdown * Remote reachable / network-triggerable: +2. The affected path processes RXRPC packets from the network when an RXRPC endpoint is exposed. * Real lifetime corruption: +1. The old code could let `skb_unshare()` consume or replace the skb and NULL out the parent pointer while the parent still expected to use it. * Weak memory corruption / UAF candidate: +1. The described failure is NULL dereference or UAF-like skb lifetime misuse, but no controlled reclaim primitive is shown. * Reliable kernel crash / strong DoS: +1. The parent `rxrpc_io_thread()` can oops in `trace_rxrpc_rx_done()` or cleanup after the pointer is NULL or consumed. * Availability impact realistic: +1. Kernel crash or RXRPC receive path failure is the main practical impact. * Common networking receive-path concern: +1. RXRPC is not universal, but this is still packet receive-path skb lifetime handling. * Hard condition: -1. Reliable triggering depends on `skb_unshare()` allocation failure or memory pressure, so AC is high. 3. Reachability analysis A remote peer can deliver secure RXRPC DATA packets to the receive path if RXRPC is enabled and reachable. No local privileges are required on the victim. Practical exploitation is harder because the dangerous branch depends on allocation failure during skb unshare, usually requiring memory pressure or constrained allocation conditions. Containers do not materially change the remote network trigger, but host exposure depends on RXRPC/AFS usage and firewalling. 4. Severity interpretation This is stronger than a simple error-handling DoS because it involves skb ownership/lifetime confusion in a network receive path. The realistic demonstrated impact is kernel oops or DoS. The paranoid interpretation reaches Strong Important candidate because network-triggerable skb lifetime bugs can be underestimated, although the patch does not prove arbitrary write, controlled UAF reclaim, information disclosure, or privilege escalation. 5. One-sentence report phrase A secure RXRPC DATA packet can hit an `skb_unshare()` failure path that consumes or clears the skb while the receive thread still uses it, causing network-triggerable DoS and a limited UAF-like lifetime concern. 6. Manual review recommendation MANUAL CHECK REQUIRED. This is network reachable in RXRPC deployments and involves skb lifetime handling after allocation failure, even though reliable exploitation depends on memory pressure and no controlled LPE primitive is shown. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: rxrpc: Fix potential UAF after skb_unshare() failure [ Upstream Commit: e3bf143b1e98fb3d6d9e6825bcd683974d478e8c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3bf143b1e98fb3d6d9e6825bcd683974d478e8c Changed files: include/trace/events/rxrpc.h net/rxrpc/ar-internal.h net/rxrpc/call_event.c net/rxrpc/io_thread.c net/rxrpc/skbuff.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=e3bf143b1e98fb3d6d9e6825bcd683974d478e8c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45998 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45998 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:N/AC:H/PR:N/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:L/I:L/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: 7 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: YES 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).