From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72042][IMPORTANT] ipmi: Fix user refcount underflow in event delivery Date: Sat, 15 Aug 2026 15:13:11 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72042 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: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: ddbb6e3dc9bb4743de686aa1598c31e745cee76b List-Id: CVE: CVE-2026-72042 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: ipmi: Fix user refcount underflow in event delivery Commit: ddbb6e3dc9bb4743de686aa1598c31e745cee76b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddbb6e3dc9bb4743de686aa1598c31e745cee76b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72042 Analysis date: Sat, 15 Aug 2026 15:13:11 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A reference-counting bug in the IPMI event delivery rollback path can prematurely free an `ipmi_user` that remains linked on `intf->users`, allowing later event delivery to dereference freed memory and potentially causing a local kernel crash or, in the worst case, a UAF-based privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72042 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72042 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-2026-72042 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-911;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A reference counting bug in the IPMI event delivery rollback path can free an ipmi_user too early. ipmi_free_recv_msg already drops the temporary user reference owned by the receive message, but the rollback path also performed an extra kref_put on the same user. The freed user may remain linked on intf users, so later event delivery can dereference freed memory or hit refcount_t add on zero checks. For the CVSS the PR:L value is used for the paranoid score because a local process with access to the IPMI device interface may be enough in deployments where /dev/ipmi is delegated to a service account or hardware management group. The issue is not directly network reachable from ordinary IP traffic. Impact is at least local denial of service via kernel crash or warning, and in the worst still defensible case may include privilege escalation due to a kernel use after free primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) SKIP CVE-2026-72042 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE OOB UAF LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local trigger with limited privileges: +1 A local process with access to the IPMI userspace interface can plausibly participate in event delivery paths. This is not ordinary remote network reachability. * Generic memory corruption, UAF/refcount lifetime class: +2 The extra `kref_put()` can free an `ipmi_user` object too early while it remains linked on `intf->users`. * Real lifetime corruption: +1 This is a concrete reference-counting lifetime bug, not just bookkeeping. * Reliable kernel crash / strong DoS: +1 Later event delivery may dereference a freed user or trigger `refcount_t` add-on-zero warnings. * Rare/configuration-dependent subsystem: -1 IPMI is common on servers but not a universal default local attack surface. Paranoid additional interpretation: * Privilege escalation plausible: +2 instead of weak concern Because the bug is a kernel UAF candidate involving a freed object that remains reachable from a global interface user list. There is no demonstrated reclaim primitive in the patch, but the refcount misuse and stale list membership make manual LPE review justified. ## 3. Reachability analysis The issue is local, not directly reachable from ordinary IP traffic. IPMI-over-LAN to a BMC should not be treated as direct access to this host kernel `ipmi_msghandler.c` path. The practical trigger requires local access to the IPMI device or a service account that can interact with the kernel IPMI interface. In typical deployments `/dev/ipmi*` may be restricted to root or a hardware-management group. That makes the conservative score lower than a fully unprivileged local bug. However, many server environments delegate IPMI access to monitoring, inventory, or management daemons, so treating this as PR:L for paranoid triage is defensible. Namespaces do not obviously make this broadly reachable unless the device node is explicitly passed through. Call-site confidence: medium-high. The patch and commit message clearly describe the ownership transfer through `ipmi_alloc_recv_msg()` and `ipmi_free_recv_msg()`, and the rollback path is visible. ## 4. Severity interpretation This is more than an ordinary Moderate cleanup because it fixes a concrete reference-counting lifetime error that can leave a freed kernel object linked for later use. The realistic demonstrated impact is local DoS through warning, oops, or crash. The theoretical but defensible higher concern is local privilege escalation from a kernel UAF primitive, although the patch does not show attacker-controlled reclaim, controlled overwrite, callback control, or a proven exploit chain. Therefore the conservative bucket is Actionable Moderate. The paranoid bucket is Strong Important candidate for manual review. ## 5. One-sentence report phrase A reference-counting bug in the IPMI event delivery rollback path can prematurely free an `ipmi_user` that remains linked on `intf->users`, allowing later event delivery to dereference freed memory and potentially causing a local kernel crash or, in the worst case, a UAF-based privilege escalation. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is a kernel refcount underflow and UAF candidate with stale list reachability. Even though exploitation beyond DoS is not demonstrated, the lifetime primitive is strong enough that it should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ipmi: Fix user refcount underflow in event delivery Commit: ddbb6e3dc9bb4743de686aa1598c31e745cee76b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddbb6e3dc9bb4743de686aa1598c31e745cee76b Commit description: ipmi_alloc_recv_msg(user) takes the temporary user reference owned by the receive message, and ipmi_free_recv_msg() drops it again. If event delivery fails after allocating receive messages for earlier users, handle_read_event_rsp() rolls those messages back with ipmi_free_recv_msg(). That rollback path still drops user->refcount explicitly after freeing each message. The extra put can free a user that remains linked on intf->users, so later event delivery may dereference a freed user or trip refcount_t's addition-on-zero warning when ipmi_alloc_recv_msg() tries to acquire another reference. Remove the stale explicit put and the now-dead user assignment. Keep the list_del() and ipmi_free_recv_msg() calls; they are the required rollback operations. Fixes: b52da40 ("ipmi: Rework user message limit handling") Cc: stable@vger.kernel.org # v6.18+ Signed-off-by: Matt Fleming Message-ID: <20260521130628.3641050-1-matt@readmodwrite.com> Signed-off-by: Corey Minyard Signed-off-by: Greg Kroah-Hartman Changed files: drivers/char/ipmi/ipmi_msghandler.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=ddbb6e3dc9bb4743de686aa1598c31e745cee76b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72042 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72042 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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 5 Paranoid ActionableScore: 7 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).