From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-52957][MODERATE 7.0] libceph: Fix potential null-ptr-deref in decode_choose_args() Date: Fri, 26 Jun 2026 14:37:01 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-52957 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: d55ffad8d422b5d1cc44dad32bd3d25f4471cd9f List-Id: CVE: CVE-2026-52957 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: libceph: Fix potential null-ptr-deref in decode_choose_args() Commit: d55ffad8d422b5d1cc44dad32bd3d25f4471cd9f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d55ffad8d422b5d1cc44dad32bd3d25f4471cd9f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52957 Analysis date: Fri, 26 Jun 2026 14:37:01 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A malformed Ceph OSD map containing CRUSH choose_args for a sparse bucket index can trigger a NULL pointer dereference in libceph decode_choose_args and crash a kernel Ceph client when the attacker can control or tamper with monitor-delivered map data. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52957 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52957 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-2026-52957 MODERATE CHECK 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-20;CWE-754;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A NULL pointer dereference in libceph OSD map decoding can occur because decode_choose_args checks that bucket_index is within max_buckets but did not verify that c buckets bucket_index is non NULL before reading the bucket size. A malformed or corrupted CEPH_MSG_OSD_MAP containing CRUSH choose_args for a sparse bucket index can therefore crash a kernel Ceph client during map decode. For the CVSS the PR:N is used because no local privileges on the victim are needed if the attacker can control or tamper with a Ceph monitor message. The issue is network reachable in Ceph deployments, but practical exploitation usually requires a malicious or compromised monitor, a trusted storage network position, or successful message tampering. Impact is denial of service via kernel crash, with no supported evidence of information disclosure or privilege escalation from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) MAYBE REMOTE READ NULLPTR SIMPLEFIX NETWORK LINUS KPANIC KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS - - 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. The affected parser handles CEPH_MSG_OSD_MAP data received by a kernel Ceph client. * Reliable kernel crash / strong DoS: +1. The patch prevents a NULL pointer dereference when c->buckets[bucket_index] is NULL. * Availability impact realistic: +1 in the paranoid score. A malicious or corrupted OSD map can plausibly crash the client kernel during decode. * Important filesystem/storage path: +1 in the paranoid score. This is in libceph OSD map handling, a storage control-plane path used by kernel Ceph clients. * Generic memory corruption: +0. The demonstrated primitive is NULL pointer dereference, not UAF, OOB write, double-free, or controlled overwrite. * Privilege escalation plausible: +0. No supported LPE primitive is visible from the patch. * Confidentiality impact plausible: +0. No read-back or information disclosure path is shown. * Integrity impact plausible: +0. The patch context supports crash prevention, not data modification or policy bypass. ## 3. Reachability analysis A remote peer can influence this path only if it can provide or tamper with Ceph OSD map messages, typically by acting as a malicious or compromised monitor, by compromising the storage control plane, or by successful MITM in a trusted Ceph network. No local privileges on the victim host are needed in that attacker model. The path is not Internet-default exposure, but it is realistic in Ceph deployments where kernel clients trust network-delivered cluster maps. ## 4. Severity interpretation This behaves as an actionable Moderate rather than a strong Important issue. The practical impact is kernel DoS through a network-delivered storage control message. The patch does not support a memory corruption primitive beyond NULL pointer dereference, and there is no evidence of privilege escalation, arbitrary write, UAF reclaim, or information disclosure. The paranoid score reaches 5 because the bug is network reachable in a real storage subsystem and can crash the kernel client. ## 5. One-sentence report phrase A malformed Ceph OSD map containing CRUSH choose_args for a sparse bucket index can trigger a NULL pointer dereference in libceph decode_choose_args and crash a kernel Ceph client when the attacker can control or tamper with monitor-delivered map data. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. This is network reachable in Ceph deployments and can cause a kernel crash, even though the supported primitive is DoS only and not privilege escalation. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: libceph: Fix potential null-ptr-deref in decode_choose_args() Commit: d55ffad8d422b5d1cc44dad32bd3d25f4471cd9f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d55ffad8d422b5d1cc44dad32bd3d25f4471cd9f Commit description: A message of type CEPH_MSG_OSD_MAP contains an OSD map that itself contains a CRUSH map. When decoding this CRUSH map in crush_decode(), an array of max_buckets CRUSH buckets is decoded, where some indices may not refer to actual buckets and are therefore set to NULL. The received CRUSH map may optionally contain choose_args that get decoded in decode_choose_args(). When decoding a crush_choose_arg_map, a series of choose_args for different buckets is decoded, with the bucket_index being read from the incoming message. It is only checked that the bucket index does not exceed max_buckets, but not that it doesn't point to an index with a NULL bucket. If a (potentially corrupted) message contains a crush_choose_arg_map including such a bucket_index, a null pointer dereference may occur in the subsequent processing when attempting to access the bucket with the given index. This patch fixes the issue by extending the affected check. Now, it is only attempted to access the bucket if it is not NULL. Cc: stable@vger.kernel.org Signed-off-by: Raphael Zimmer Reviewed-by: Ilya Dryomov Signed-off-by: Ilya Dryomov Signed-off-by: Greg Kroah-Hartman Changed files: net/ceph/osdmap.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=d55ffad8d422b5d1cc44dad32bd3d25f4471cd9f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52957 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52957 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: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: 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).