From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74425][MODERATE REGULAR] afs: handle CB.InitCallBackState3 requests without a server record Date: Sun, 16 Aug 2026 06:12:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74425 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 42e3917cdbdc3d35e191c525687a6d5427f237fd List-Id: CVE: CVE-2026-74425 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: afs: handle CB.InitCallBackState3 requests without a server record Commit: 42e3917cdbdc3d35e191c525687a6d5427f237fd Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=42e3917cdbdc3d35e191c525687a6d5427f237fd Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74425 Analysis date: Sun, 16 Aug 2026 06:12:15 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline, manual review recommended / Actionable Moderate consideration Manual review required: YES Summary: AFS CB.InitCallBackState3 can dereference a missing server record for an unmatched RxRPC callback request, allowing a reachable remote peer to crash the kernel through a NULL pointer dereference. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74425 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74425 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 REGULAR 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-2026-74425 MODERATE CHECK WITH IMPACT FROM ORIG NN NONE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-703;CWE-754;BEST CVSS score: '7.5';DESCR 'AFS CB.InitCallBackState3 handling can dereference a missing server record when an incoming RxRPC callback request is not mapped to a known AFS server. A remote peer that can reach the AFS callback service may trigger this path with an unmatched callback request, causing a NULL pointer dereference and kernel crash. For the CVSS the PR:N is selected because the attacker does not need local privileges on the victim and only needs network reachability to the AFS callback service. The issue is network reachable in AFS deployments where callback traffic from untrusted or spoofable peers can reach the client. Impact is denial of service only via kernel crash. No evidence of UAF, OOB access, information disclosure, or privilege escalation is supported by this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended / Actionable Moderate consideration (with actual score 4) SKIP CVE-2026-74425 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 40e8b52fe8c8ab6920ea5f59c5469b6918cce624 YES NO NO unknown MAYBE DANGER DISK SIMPLEFIX SKIP LINUS INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended / Actionable Moderate consideration**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2 The affected path is an AFS cache manager callback handler over RxRPC. A peer that can reach the callback service may send an unmatched CB.InitCallBackState3 request. * Reliable kernel crash / strong DoS: +1 The old code dereferences `call->server->_uuid` without checking `call->server`. If no server record is attached, this is a NULL pointer dereference in kernel context. * Rare AND difficult-to-reach subsystem/configuration: -1 AFS is not commonly enabled or exposed on most general-purpose systems. Practical exposure depends on AFS client usage and callback reachability. * Availability impact realistic: +1 Counted in the paranoid score only. If the callback service is reachable, the NULL dereference is a direct kernel crash path. Not counted: * Generic memory corruption: +0 This is a NULL pointer dereference, not UAF, OOB write, double free, type confusion, or arbitrary write. * Privilege escalation plausible: +0 No reclaim, stale object reuse, writable stale object, callback hijack, or refcount takeover is shown. * Confidentiality / Integrity: +0 The supported impact is DoS only. ## 3. Reachability analysis The bug can be triggered by a remote peer able to send AFS/RxRPC callback traffic to the affected client. No local account on the victim is required if the callback service is reachable, so the practical CVSS-style PR interpretation is PR:N. Containers and namespaces are not the main factor here because the trigger is network-side callback handling. The main limiting condition is deployment exposure: AFS is relatively uncommon, and many systems will not run an AFS client or expose callback traffic to untrusted networks. Call-site confidence: medium. The patch shows the direct dereference site and the missing NULL check, but broader callback service exposure depends on runtime AFS configuration. ## 4. Severity interpretation This behaves like a network-reachable DoS issue, not an Important-class memory corruption vulnerability. The theoretical impact is limited by the primitive: the patch supports a NULL dereference, but not UAF, OOB access, attacker-controlled overwrite, information leak, or privilege escalation. Because the path is network reachable when AFS callbacks are exposed, it should not be auto-closed without checking affected product exposure. ## 5. One-sentence report phrase AFS CB.InitCallBackState3 can dereference a missing server record for an unmatched RxRPC callback request, allowing a reachable remote peer to crash the kernel through a NULL pointer dereference. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Network reachability makes this worth manual triage even though the primitive is DoS-only. The key product-specific question is whether AFS client callback handling is enabled and reachable from untrusted peers. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: afs: handle CB.InitCallBackState3 requests without a server record Commit: 42e3917cdbdc3d35e191c525687a6d5427f237fd Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=42e3917cdbdc3d35e191c525687a6d5427f237fd Commit description: The cache manager callback path now attaches the server record to an incoming call through the rxrpc peer's app data. That association is not guaranteed to exist for every callback request, and most callback handlers already tolerate that case. Make CB.InitCallBackState3 follow the same pattern by checking whether a server record was attached before using it. If the peer is not mapped to a server record, trace the request and ignore it, matching the existing behaviour for other unmatched callback requests. This keeps the callback handler consistent with the rest of the cache manager service and avoids depending on peer state that may not be available for a given request. Fixes: 40e8b52 ("afs: Use the per-peer app data provided by rxrpc") Cc: stable@kernel.org Reported-by: Yuan Tan Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Xin Liu Signed-off-by: Nan Li Signed-off-by: Ren Wei Signed-off-by: David Howells Link: https://patch.msgid.link/20260622090856.2746629-2-dhowells@redhat.com cc: Marc Dionne cc: linux-afs@lists.infradead.org Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman Changed files: fs/afs/cmservice.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=42e3917cdbdc3d35e191c525687a6d5427f237fd ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74425 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74425 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: Not available The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 7.5 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: 3 Paranoid ActionableScore: 4 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: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).