From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72217][IMPORTANT] SUNRPC: Bound-check xdr_buf_to_bvec() stores before writing Date: Sun, 16 Aug 2026 05:29:50 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72217 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: 9 X-AL-KERNEL-ActionableScore-Lower: 8 X-AL-KERNEL-Commit: 4a1148f2739d5089c3ca8ae2e9d1053e219ab5df List-Id: CVE: CVE-2026-72217 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: SUNRPC: Bound-check xdr_buf_to_bvec() stores before writing Commit: 4a1148f2739d5089c3ca8ae2e9d1053e219ab5df Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4a1148f2739d5089c3ca8ae2e9d1053e219ab5df Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72217 Analysis date: Sun, 16 Aug 2026 05:29:50 -0400 ActionableScore: 9 ActionableScore lower bound: 8 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: SUNRPC `xdr_buf_to_bvec()` can write one `bio_vec` past the caller-provided array before bounds checking, allowing a network-reachable NFS client to corrupt adjacent kernel slab memory and potentially crash the server or cause broader kernel memory corruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72217 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72217 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-2026-72217 IMPORTANT CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-119;*CWE-20;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'SUNRPC xdr_buf_to_bvec can write one bio_vec past the caller supplied array because the old code stored into bvec before checking count against bvec_size, and the head branch had no bounds check. In the nfsd_vfs_write path the rq_bvec array is allocated with exactly rq_maxpages entries, so the surplus store can corrupt adjacent slab memory with bv_len and bv_offset values influenced by RPC payload layout and sizes. For the CVSS the PR:L is used because reliable triggering normally requires an NFS client identity or export access capable of sending write RPC traffic to the server. The issue is network reachable when an NFS server is exposed to the attacker, but NFS services are commonly limited to trusted storage or data center networks rather than the public Internet. Impact is at least denial of service via kernel memory corruption and in the paranoid case may include confidentiality or integrity impact, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 9) SKIP CVE-2026-72217 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 2eb2b93581813b74c7174961126f6ec38eadb5a7 YES NO NO unknown MAYBE REMOTE WRITE OOB SIMPLEFIX NETWORK TEST KPANIC MEMORY KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=9 ActionableScoreLower=8 ## 1. ActionableScore * Conservative score: 8 * Paranoid score: 9 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Remote reachable / network-triggerable: +2 The affected path is SUNRPC/NFS server-side handling. A malicious or authorized NFS client can influence RPC payload layout and sizes. * Memory corruption, strong corruption primitive: +2 The bug is an out-of-bounds write of one `bio_vec` past the caller-provided array. The commit explicitly says the store can land in adjacent slab memory. * Weak LPE concern: +1 The overwrite target is adjacent slab memory and not fully attacker-selected, but this is still kernel heap corruption in a network service with partially attacker-influenced fields. * Reliable kernel crash / strong DoS: +1 Adjacent slab corruption in the NFS server path can realistically produce kernel crash or service disruption. * Confidentiality impact plausible: +1 Not directly demonstrated, but kernel heap corruption in a remote server path can plausibly affect object state in ways that may expose data in worst-case triage. * Integrity impact plausible: +1 The OOB write modifies adjacent kernel memory. Even if constrained, integrity impact is plausible. * Broad/default/common subsystem or broadly deployed exposure: +1 NFS/SUNRPC is a common server subsystem, especially in storage and data-center environments. No subtraction is applied for rare configuration. NFS is often access-controlled and not Internet-facing, but it is not a rare or exotic kernel path. ## 3. Reachability analysis The bug is triggerable from the network when an NFS server is reachable and the attacker can send relevant RPC write traffic. In realistic deployments this often means access to an exported NFS share or to a trusted storage network, so it is not necessarily public-Internet reachable. Namespaces do not materially reduce the server-side risk once the NFS service is exposed. The path is not a local-only ioctl or admin-only configuration path. Exploitation conditions depend on shaping the xdr buffer so that the caller bvec budget is exactly exhausted and the next head/page/tail store occurs one slot past the allocated `rq_bvec` array. ## 4. Severity interpretation This behaves closer to an Important-class kernel vulnerability than an ordinary Moderate issue. The realistic demonstrated impact is kernel memory corruption and likely DoS. The theoretical worst case includes confidentiality or integrity impact because the bug writes beyond a slab allocation in a network-reachable server path, although the overwrite is constrained to a `bio_vec`-shaped store and does not directly show arbitrary write or controlled object replacement. Conservative handling should still require manual review because remote kernel OOB writes are historically high-risk even when the first visible symptom is crash prevention. ## 5. One-sentence report phrase SUNRPC `xdr_buf_to_bvec()` can write one `bio_vec` past the caller-provided array before bounds checking, allowing a network-reachable NFS client to corrupt adjacent kernel slab memory and potentially crash the server or cause broader kernel memory corruption. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a network-reachable kernel out-of-bounds write in the NFS/SUNRPC server path, with adjacent slab corruption explicitly described and client-influenced length or offset fields. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: SUNRPC: Bound-check xdr_buf_to_bvec() stores before writing Commit: 4a1148f2739d5089c3ca8ae2e9d1053e219ab5df Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4a1148f2739d5089c3ca8ae2e9d1053e219ab5df Commit description: xdr_buf_to_bvec() writes a bio_vec into the caller's array before testing whether that slot is in range, and the head branch performs the store with no check at all. When the caller's budget is exactly used up, the next store lands one element past the end of the array. The overflow label returns count - 1, which masks the surplus store but cannot undo it. rq_bvec, the array passed by nfsd_vfs_write(), is allocated to exactly rq_maxpages entries with no slack. The OOB store can land in adjacent slab memory; the bv_len and bv_offset fields written there are derived from client-supplied RPC payload sizes. Move the in-range check ahead of the store in the head, page-loop, and tail branches. With the check at the top of each sequence, count is incremented only after a successful store, so the overflow label can return count directly. Reported-by: Chris Mason Fixes: 2eb2b93 ("SUNRPC: Convert svc_tcp_sendmsg to use bio_vecs directly") Cc: stable@vger.kernel.org Reviewed-by: Jeff Layton Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman Changed files: net/sunrpc/xdr.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=4a1148f2739d5089c3ca8ae2e9d1053e219ab5df ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72217 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72217 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:L/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 8.8 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: 8 Paranoid ActionableScore: 9 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).