CVE-2026-80727 in Linux
Summary
by MITRE • 09/03/2026
In the Linux kernel, the following vulnerability has been resolved:
x86/mce: Set up the polling timer before CMCI discovery
I hit the following on one of my machines:
mce: CPU0 BANK15 CMCI inherited storm ------------[ cut here ]------------
ODEBUG: assert_init not available (active state 0) object: (____ptrval____) object type: timer_list hint: 0x0 WARNING: lib/debugobjects.c:632 at debug_object_assert_init+0x178/0x230, CPU#0: swapper/0/0 CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 7.2.0-rc5 #3 PREEMPTLAZY RIP: 0010:debug_object_assert_init+0x18f/0x230 Call Trace: <TASK> __mod_timer mce_timer_kick cmci_discover intel_init_cmci mce_intel_feature_init mcheck_cpu_init identify_cpu identify_boot_cpu arch_cpu_finalize_init start_kernel
A second splat follows right after, from timer_setup() finding that same timer already queued:
ODEBUG: init active (active state 0) object: (____ptrval____) object type: timer_list hint: stub_timer+0x0/0x10
This is happening because CMCI storm detection is trying to modify the timer before latter was properly set up.
Set up the timer first. __mcheck_cpu_setup_timer() only calls timer_setup(), and depends on neither the generic nor the vendor init.
[ bp: Massage commit message. ]
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Analysis
by VulDB Data Team • 09/03/2026
The vulnerability described involves a race condition in the Linux kernel's Machine Check Architecture (MCA) subsystem, specifically within the x86 implementation of Computer-Machine Check Interrupt (CMCI) handling. The core issue stems from an incorrect initialization sequence where the polling timer required for detecting CMCI storms is not established before the system attempts to utilize it during the discovery phase. This ordering error leads to undefined behavior when the kernel tries to interact with a timer object that has not been properly initialized, resulting in critical debugging assertions and potential stability issues on affected systems running vulnerable kernel versions such as 7.2.0-rc5.
The technical flaw occurs because the CMCI storm detection mechanism relies on a periodic polling timer to monitor hardware error thresholds. During CPU initialization, specifically within the intel_init_cmci function which is called by mce_intel_feature_init and subsequently mcheck_cpu_init, the kernel attempts to kick this timer via cmci_discover before it has been set up. The debug object subsystem detects that the timer_list object is in an uninitialized state when __mod_timer is invoked, triggering a warning from debug_object_assert_init. This indicates that the code attempted to modify or schedule a timer that was not yet constructed through timer_setup(). Immediately following this failure, a second error occurs where timer_setup() finds the same timer already queued or improperly initialized, further confirming the race condition and improper state management of kernel timers during early boot initialization.
From an operational perspective, this vulnerability can cause system instability during the boot process on systems equipped with Intel processors that support CMCI. The immediate impact is visible through kernel warnings and potential panics if debug objects are enabled or if the error handling paths lead to further failures. While it may not always result in a complete system crash depending on configuration, it disrupts the reliable initialization of hardware error monitoring mechanisms. This can leave the system without proper protection against machine check errors that could otherwise be mitigated by CMCI storm detection, potentially leading to silent data corruption or unexpected reboots if actual hardware errors occur later and are not properly managed due to the compromised initialization state.
This issue aligns with CWE-362, Concurrent Execution using Shared Resource with Improper Synchronization, as it involves a race condition in resource initialization where one component accesses another before it is ready. It also relates to CWE-824, Access of Uninitialized Pointer/Resource, since the timer object is accessed without being properly initialized first. In terms of MITRE ATT&CK mapping, this does not represent an exploit vector for attackers but rather a reliability flaw in system initialization logic that could be leveraged indirectly if combined with other vulnerabilities to cause denial of service during boot sequences or early runtime operations.
The mitigation involves ensuring the correct ordering of initialization functions within the MCA subsystem. Specifically, __mcheck_cpu_setup_timer must be called before any code path attempts to use the timer for CMCI discovery. This function solely handles the setup of the timer via timer_setup and does not depend on generic or vendor-specific initialization routines, making it safe to execute early in the boot process. By establishing the polling timer prior to invoking cmci_discover, the kernel ensures that all subsequent interactions with the timer object occur against a properly initialized structure, thereby preventing the assertion failures and ensuring robust error handling capabilities for machine check events.