From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72122][MODERATE REGULAR] can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Date: Sat, 15 Aug 2026 06:18:44 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72122 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: 9e60c586faeaed80d55ab8ce2a4b8e56133bc395 List-Id: CVE: CVE-2026-72122 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Commit: 9e60c586faeaed80d55ab8ce2a4b8e56133bc395 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9e60c586faeaed80d55ab8ce2a4b8e56133bc395 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72122 Analysis date: Sat, 15 Aug 2026 06:18:44 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A local race in CAN BCM can make bcm_sendmsg observe inconsistent bound and ifindex state, temporarily allowing a socket bound to one CAN interface to behave like an any-interface socket, with limited confidentiality or integrity impact and no demonstrated memory corruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72122 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72122 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-2026-72122 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L';CWE-362;CWE-667;CWE-284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '4.5';DESCR 'A race in CAN BCM can let bcm_sendmsg observe bo bound and bo ifindex in an inconsistent state while another path updates the same socket under lock_sock. This can temporarily turn a socket that was intended to be bound to one CAN interface into behavior similar to an any interface binding, which may expose or send CAN BCM traffic outside the expected interface scope. For the CVSS the PR:L is used because a local process must create and operate a CAN BCM socket and reliably race sendmsg with connect or device unregister related state changes. The issue is not directly reachable from an IP network and is triggered through local socket control paths. Impact is mainly a local interface scope bypass with limited confidentiality or integrity impact, and possible local availability impact for affected CAN applications rather than a proven kernel memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) YES DISK INIT RACE HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 A local process can operate a CAN BCM socket if PF_CAN/CAN_BCM is available and policy allows socket creation. * Cross-boundary isolation/policy bypass: +1 The race can make a socket intended to be bound to one CAN interface behave like an any-interface binding. This may cross an intended local CAN interface scope boundary. * Confidentiality impact plausible: +1 Limited exposure of CAN BCM traffic outside the expected interface scope is plausible. * Integrity impact plausible: +1 Limited unintended sending or matching of CAN BCM operations across interface scope is plausible. * Hard or unreliable race / special timing required: -1 The bug depends on racing bcm_sendmsg() with bcm_notify(), bcm_connect(), or device unregister state changes. Paranoid-only signal: * Availability impact realistic: +1 The silent RX_SETUP success and broken RX operation may cause local application-level availability impact, but there is no demonstrated reliable kernel crash. Not triggered: * No generic memory corruption signal. The patch does not show UAF, OOB write, double free, stale callback, refcount takeover, or type confusion. * No privilege escalation signal. The visible primitive is interface-scope confusion, not a kernel memory corruption or credential/capability takeover primitive. * No remote reachable signal. This is not directly reachable from an IP network. It requires local CAN socket operations. ## 3. Reachability analysis The likely trigger is a local process using CAN BCM sockets and racing sendmsg against connect or device unregister related state changes. Namespaces may matter if an untrusted user can access CAN sockets or CAN devices inside a delegated network namespace, but creating or managing CAN/vcan interfaces normally requires CAP_NET_ADMIN. The affected path is not common on general-purpose servers, but it is reachable through ordinary local socket APIs on systems with SocketCAN/CAN BCM enabled and usable CAN interfaces. Call-site confidence: high, because the relevant bcm_sendmsg(), bcm_notify(), bcm_connect(), bcm_release(), and bcm_rx_setup() paths are visible in the patch. ## 4. Severity interpretation This behaves like a borderline actionable Moderate rather than an Important-class kernel vulnerability. The theoretical security impact is a local policy or interface-scope bypass between CAN interfaces with limited confidentiality and integrity impact. Realistic exploitation evidence is weaker because the primitive is race-dependent and there is no demonstrated memory corruption, kernel crash, privilege escalation, or remote network trigger. The issue should not be treated as a high-end kernel memory-corruption CVE based on the supplied patch. ## 5. One-sentence report phrase A local race in CAN BCM can make bcm_sendmsg observe inconsistent bound and ifindex state, temporarily allowing a socket bound to one CAN interface to behave like an any-interface socket, with limited confidentiality or integrity impact and no demonstrated memory corruption. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because this is a race in a networking subsystem and the real impact depends on local CAN access policy, namespace delegation, and whether multiple CAN interfaces represent different trust domains. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: can: bcm: fix lockless bound/ifindex race and silent RX_SETUP failure Commit: 9e60c586faeaed80d55ab8ce2a4b8e56133bc395 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9e60c586faeaed80d55ab8ce2a4b8e56133bc395 Commit description: bcm_sendmsg() reads bo->ifindex and checks bo->bound before taking lock_sock(), while bcm_notify(), bcm_connect() and bcm_release() all mutate both fields under that same lock. Because the lockless reads and the locked writes are unordered with respect to each other, a racing bcm_notify() (device unregister) or bcm_connect() (concurrent bind on another thread sharing the socket) can make bcm_sendmsg() observe an inconsistent combination, e.g. a stale bound=1 together with the now-cleared ifindex=0, silently turning a socket bound to a specific CAN interface into one that also matches "any" interface. Keep the lockless bo->bound check purely as a fast-path reject, and move the ifindex read (and a bo->bound re-check) into the locked section, where every writer already serializes. This removes the possibility of observing the two fields torn against each other, rather than trying to fix it with more READ_ONCE()/WRITE_ONCE() pairs on two independently updated fields. Annotate the now-purely-lockless bo->bound accesses consistently across all its write sites. Also fix bcm_rx_setup() silently returning success when the target device disappears concurrently instead of reporting -ENODEV, so a broken RX op is no longer left registered as if it had succeeded. Fixes: ffd980f ("[CAN]: Add broadcast manager (bcm) protocol") Reported-by: Ginger Closes: https://lore.kernel.org/linux-can/CAGp+u1aBK8QVjsvAxM2Ldzep4rEbsP9x_pV3At4g=h1kVEtyhA@mail.gmail.com/ Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20260714-bcm_fixes-v15-2-562f7e3e42da@hartkopp.net Cc: stable@kernel.org Signed-off-by: Marc Kleine-Budde Signed-off-by: Greg Kroah-Hartman Changed files: net/can/bcm.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=9e60c586faeaed80d55ab8ce2a4b8e56133bc395 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72122 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72122 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:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L The Best / paranoid CVSS score: 4.5 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).