From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-31532][MODERATE 7.0] can: raw: fix ro->uniq use-after-free in raw_rcv() Date: Tue, 09 Jun 2026 18:00:09 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-31532 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: 572f0bf536ebc14f6e7da3d21a85cf076de8358e List-Id: CVE: CVE-2026-31532 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: can: raw: fix ro->uniq use-after-free in raw_rcv() Commit: 572f0bf536ebc14f6e7da3d21a85cf076de8358e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=572f0bf536ebc14f6e7da3d21a85cf076de8358e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31532 Analysis date: Tue, 09 Jun 2026 18:00:09 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A race in CAN RAW socket teardown can free `ro->uniq` before deferred RCU receive callbacks have drained, allowing `raw_rcv()` to access freed percpu storage and potentially crash the kernel. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-31532 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31532 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-2026-31532 MODERATE CHECK 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-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in the CAN RAW receive path because raw_release() frees the per CPU uniq storage while receiver removal is still deferred through RCU. raw_rcv() may still run inside an RCU read side critical section and access the freed ro uniq storage after can_rx_unregister() has returned. For the CVSS the PR:L is used because reliable triggering requires local code execution with access to CAN RAW sockets or delegated CAP_NET_RAW like capability, not full administrator control. The issue is not directly reachable over an IP network and is primarily a local attack surface, although CAN frame delivery can help exercise the receive path during the race window. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact due to kernel use-after-free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES 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 Conservative signals: * Memory corruption, weak primitive: +1. This is a real UAF, but it is race dependent and the patch only shows stale access to freed percpu storage, not attacker controlled reclaim, overwrite, callback dispatch, or type confusion. * Real lifetime corruption: +1. The bug is an RCU lifetime mismatch between `raw_release()`, deferred receiver deletion via `call_rcu()`, and later `raw_rcv()` access. * Reliable kernel crash / strong DoS: +1. A stale percpu pointer in the receive path can plausibly cause an Oops or kernel crash. * Local reduced privilege trigger: +1. Triggering requires local access to CAN RAW sockets or delegated capability such as CAP_NET_RAW, but not full host root in all deployments. * Hard or timing dependent race: -1. The issue depends on an RCU teardown window between socket release and receive callback execution. Paranoid adjustment: * Do not downgrade for race difficulty in the paranoid score: +1 relative to conservative. The receive path and socket close path are both locally influenceable, and CAN frame delivery may make the race reproducible under stress. * No LPE bonus is awarded. The patch does not show attacker controlled reclaim, write after free, type confusion, callback corruption, or refcount takeover. ## 3. Reachability analysis The bug is locally reachable through the CAN RAW socket path. A practical trigger needs a local process able to create or use CAN RAW sockets and to exercise receive filters while closing the socket. In many systems this implies CAP_NET_RAW or a similarly delegated capability, but it is not equivalent to full host root or CAP_SYS_ADMIN. The issue is not directly reachable over normal IP networking. External CAN traffic may help exercise `raw_rcv()`, but the vulnerable lifetime transition is controlled by local socket release and filter unregister activity. Containers or namespaces matter if CAN access or CAP_NET_RAW is delegated to a less trusted workload. The affected subsystem is not a broad default Internet facing path. It is relevant on systems using SocketCAN, vcan, CAN gateways, automotive, industrial, or test environments. ## 4. Severity interpretation This is more than an ordinary Moderate cleanup because it is an explicit kernel use after free in an RCU receive path. Realistic demonstrated impact is local DoS, and the available patch context does not prove a practical privilege escalation primitive. Theoretical memory corruption potential exists because freed percpu storage can be accessed after release. However, the evidence does not show controlled object replacement, attacker controlled payload, arbitrary write, or callback hijack. Therefore the conservative result is borderline manual review, while the paranoid result reaches Actionable Moderate. ## 5. One-sentence report phrase A race in CAN RAW socket teardown can free `ro->uniq` before deferred RCU receive callbacks have drained, allowing `raw_rcv()` to access freed percpu storage and potentially crash the kernel. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a real UAF plus RCU lifetime bug in a kernel receive path. Even though current evidence mainly supports DoS, lifetime bugs of this class should not be auto-closed without confirming whether percpu reuse or receive-path behavior can produce a stronger primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: can: raw: fix ro->uniq use-after-free in raw_rcv() Commit: 572f0bf536ebc14f6e7da3d21a85cf076de8358e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=572f0bf536ebc14f6e7da3d21a85cf076de8358e Commit description: raw_release() unregisters raw CAN receive filters via can_rx_unregister(), but receiver deletion is deferred with call_rcu(). This leaves a window where raw_rcv() may still be running in an RCU read-side critical section after raw_release() frees ro->uniq, leading to a use-after-free of the percpu uniq storage. Move free_percpu(ro->uniq) out of raw_release() and into a raw-specific socket destructor. can_rx_unregister() takes an extra reference to the socket and only drops it from the RCU callback, so freeing uniq from sk_destruct ensures the percpu area is not released until the relevant callbacks have drained. Fixes: 514ac99 ("can: fix multiple delivery of a single CAN frame for overlapping CAN filters") Cc: stable@vger.kernel.org # v4.1+ Assisted-by: Bynario AI Signed-off-by: Samuel Page Link: https://patch.msgid.link/26ec626d-cae7-4418-9782-7198864d070c@bynar.io Acked-by: Oliver Hartkopp [mkl: applied manually] Signed-off-by: Marc Kleine-Budde Signed-off-by: Greg Kroah-Hartman Changed files: net/can/raw.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=572f0bf536ebc14f6e7da3d21a85cf076de8358e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-31532 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-31532 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:L/I:L/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: 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).