From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-68155][MODERATE 7.0] libceph: Reject monmaps advertising zero monitors Date: Mon, 10 Aug 2026 18:37:39 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-68155 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: 0591a15815b498be628a937146e44487d599ba33 List-Id: CVE: CVE-2026-68155 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: libceph: Reject monmaps advertising zero monitors Commit: 0591a15815b498be628a937146e44487d599ba33 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0591a15815b498be628a937146e44487d599ba33 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68155 Analysis date: Mon, 10 Aug 2026 18:37:39 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A malicious or compromised Ceph monitor can send a corrupted monmap with zero monitors, causing the kernel Ceph client to hit `BUG_ON` during monitor session setup and crash the system. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68155 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68155 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-2026-68155 MODERATE CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-20;CWE-617;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 'libceph accepted a corrupted monitor map with num_mon equal to 0 even though a valid Ceph cluster cannot have zero monitors and still provide a usable monmap to a client. A malicious or compromised Ceph monitor, or an attacker able to tamper with monitor traffic, can send such a monmap and cause the client to hit BUG_ON in pick_new_mon while opening a monitor session. For the CVSS the PR:N means no privileges are required on the victim system beyond network reachability to the Ceph monitor path. The base score uses AC:H because practical triggering usually depends on control of a trusted monitor endpoint or traffic tampering. The issue is network reachable in Ceph deployments, but Ceph monitor traffic is usually limited to storage or data center networks rather than exposed to the public Internet. Impact is denial of service via kernel crash only.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES REMOTE DANGER SIMPLEFIX NETWORK KERNEL_PANIC_PLUS_UAF LINUS KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 NO NO 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 malformed `CEPH_MSG_MON_MAP` is received over the Ceph monitor protocol path. * Reliable kernel crash / strong DoS: +1. A zero-monitor monmap can reach `pick_new_mon()` and trigger `BUG_ON(monc->monmap->num_mon < 1)`. * Availability impact realistic: +1. The described failure is a kernel crash on the client, not only a recoverable protocol error. * Broad/default/common subsystem: +0. Ceph is important in storage environments but not a default universal kernel exposure. * Memory corruption: +0. The patch shows input validation preventing an assertion-triggered crash, not UAF, OOB write, type confusion, or arbitrary write. * Privilege escalation plausible: +0. No supported LPE primitive is visible from the patch or commit message. * Rare/config-dependent exposure: conservative 0, not -1. Ceph client usage is deployment-specific, but the affected path is normal for systems using Ceph. ## 3. Reachability analysis An attacker needs the victim kernel Ceph client to accept a monmap from an attacker-controlled, compromised, or traffic-tampered Ceph monitor path. No local privileges are required on the victim host in that scenario. This is not general Internet exposure in most deployments because Ceph monitors are usually on storage or data-center networks. Containers and namespaces are not the main factor here. The practical precondition is access to the Ceph monitor communication path or control of a monitor endpoint. Call-site confidence: high. The commit explicitly names the downstream crash path through `__open_session()`, `pick_new_mon()`, and `BUG_ON`. ## 4. Severity interpretation This behaves like an actionable network-reachable DoS, not an Important-class memory corruption issue. The theoretical impact is limited by the visible primitive: malformed input causes an assertion failure and kernel crash. There is no evidence of confidentiality impact, integrity impact, object lifetime corruption, attacker-controlled overwrite, or privilege escalation. The issue should not be auto-closed as a low-priority Moderate because it is remotely deliverable in affected Ceph deployments and can crash the kernel client. ## 5. One-sentence report phrase A malicious or compromised Ceph monitor can send a corrupted monmap with zero monitors, causing the kernel Ceph client to hit `BUG_ON` during monitor session setup and crash the system. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: network-reachable kernel crash in a storage protocol path. The current evidence supports DoS only, but exposure and deployment assumptions should be verified for affected products. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: libceph: Reject monmaps advertising zero monitors Commit: 0591a15815b498be628a937146e44487d599ba33 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0591a15815b498be628a937146e44487d599ba33 Commit description: A message of type CEPH_MSG_MON_MAP contains a monmap that is sent from a monitor to the client. This monmap contains information about the existing monitors in the cluster. Currently, a monmap indicating that there are zero monitors in the cluster is treated as valid. However, it is impossible to have zero monitors in the cluster and still receive a valid monmap from a monitor. Therefore, such a monmap must be corrupted and should be treated as invalid. Furthermore, a monmap with a monitor count of zero can subsequently crash the client when attempting to open a session with a monitor in __open_session(). This happens because the "BUG_ON(monc->monmap->num_mon < 1)" assertion in pick_new_mon() is triggered. This patch extends a check in ceph_monmap_decode() to also reject arriving mon_maps with num_mon == 0 rather than only with num_mon > CEPH_MAX_MON. [ idryomov: drop "log output for unusual values of num_mon" part ] 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/mon_client.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=0591a15815b498be628a937146e44487d599ba33 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68155 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68155 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).