From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45983][MODERATE 7.0] nfsd: never defer requests during idmap lookup [ Upstream Date: Wed, 27 May 2026 18:16:05 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45983 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: b9abb760db20504240a7147f27934d900cd80b23 List-Id: CVE: CVE-2026-45983 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: nfsd: never defer requests during idmap lookup [ Upstream Commit: b9abb760db20504240a7147f27934d900cd80b23 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9abb760db20504240a7147f27934d900cd80b23 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45983 Analysis date: Wed, 27 May 2026 18:16:05 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45983 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45983 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-45983 MODERATE 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:N/I:N/A:H';CWE-703;CWE-755;**CWE-400;CWE-667;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'NFSv4 compound decoding can trigger idmap upcalls while RQ_USEDEFERRAL is still enabled. If the upcall response is delayed, cache_check() can mark the request for deferral and drop it before response encoding, leaving an NFSv4.1 session slot marked INUSE. For the CVSS the PR:N is used because a remote NFSv4 client that can reach the export can send requests that exercise idmap lookup paths, although reliable triggering depends on delayed idmap upcall handling. The issue is network reachable in NFSv4 server deployments. Impact is denial of service through leaked session slots and NFSERR_JUKEBOX for subsequent client requests, with no supported memory corruption or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) MAYBE DISK LEAK NETWORK KPANIC - - 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 * Remote reachable / network-triggerable: +2. A remote NFSv4 client can send compound operations that trigger idmap lookup paths. * Reliable service DoS: +1. A deferred and dropped request can leave an NFSv4.1 session slot permanently marked `INUSE`, causing later requests to fail with `NFSERR_JUKEBOX`. * Availability impact realistic: +1. The impact is client-visible denial of service through leaked session slots. * Broad/common server exposure: +1. NFSv4 server deployments are common enough to warrant attention. * Hard condition / special timing: -1. Reliable triggering depends on delayed idmap upcall responses beyond the allowed cache timeout. * No memory corruption signal. The patch fixes request deferral/session-slot state handling, not UAF, OOB, arbitrary write, or info leak. 3. Reachability analysis The issue is reachable by a remote NFSv4 client that can access the server and send operations such as `SETATTR` that require idmap lookup during compound argument decoding. No local privileges are required on the server. Practical exploitation depends on the ability to cause or coincide with delayed idmap upcalls, which may require environmental pressure, idmap service latency, or crafted identities that miss cache. Namespaces do not materially affect the remote server-side trigger. 4. Severity interpretation This is a network-reachable availability issue, not a memory-corruption vulnerability. Conservative severity is borderline because the trigger depends on idmap delay. Paranoid severity is Actionable Moderate because the result can permanently consume NFSv4.1 session slots for a client and cause persistent service disruption without requiring local access. 5. One-sentence report phrase A remote NFSv4 client can trigger idmap upcall deferral during compound decoding, causing dropped requests to leak NFSv4.1 session slots and produce persistent `NFSERR_JUKEBOX` denial of service. 6. Manual review recommendation MANUAL CHECK RECOMMENDED. The bug is network reachable in NFSv4 server deployments and can cause persistent session-slot DoS, but no memory corruption, information disclosure, or privilege escalation is shown. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nfsd: never defer requests during idmap lookup [ Upstream Commit: b9abb760db20504240a7147f27934d900cd80b23 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9abb760db20504240a7147f27934d900cd80b23 Changed files: fs/nfsd/nfs4idmap.c fs/nfsd/nfs4proc.c fs/nfsd/nfs4xdr.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=b9abb760db20504240a7147f27934d900cd80b23 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45983 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45983 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:L The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.9 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).