CVE-2026-23088 in Linux
Summary
by MITRE • 02/04/2026
In the Linux kernel, the following vulnerability has been resolved:
tracing: Fix crash on synthetic stacktrace field usage
When creating a synthetic event based on an existing synthetic event that had a stacktrace field and the new synthetic event used that field a kernel crash occurred:
~# cd /sys/kernel/tracing ~# echo 's:stack unsigned long stack[];' > dynamic_events
~# echo 'hist:keys=prev_pid:s0=common_stacktrace if prev_state & 3' >> events/sched/sched_switch/trigger ~# echo 'hist:keys=next_pid:s1=$s0:onmatch(sched.sched_switch).trace(stack,$s1)' >> events/sched/sched_switch/trigger
The above creates a synthetic event that takes a stacktrace when a task schedules out in a non-running state and passes that stacktrace to the sched_switch event when that task schedules back in. It triggers the "stack" synthetic event that has a stacktrace as its field (called "stack").
~# echo 's:syscall_stack s64 id; unsigned long stack[];' >> dynamic_events
~# echo 'hist:keys=common_pid:s2=stack' >> events/synthetic/stack/trigger ~# echo 'hist:keys=common_pid:s3=$s2,i0=id:onmatch(synthetic.stack).trace(syscall_stack,$i0,$s3)' >> events/raw_syscalls/sys_exit/trigger
The above makes another synthetic event called "syscall_stack" that attaches the first synthetic event (stack) to the sys_exit trace event and records the stacktrace from the stack event with the id of the system call that is exiting.
When enabling this event (or using it in a historgram):
~# echo 1 > events/synthetic/syscall_stack/enable
Produces a kernel crash!
BUG: unable to handle page fault for address: 0000000000400010 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP PTI
CPU: 6 UID: 0 PID: 1257 Comm: bash Not tainted 6.16.3+deb14-amd64 #1 PREEMPT(lazy) Debian 6.16.3-1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 RIP: 0010:trace_event_raw_event_synth+0x90/0x380 Code: c5 00 00 00 00 85 d2 0f 84 e1 00 00 00 31 db eb 34 0f 1f 00 66 66 2e 0f 1f 84 00 00 00 00 00 66 66 2e 0f 1f 84 00 00 00 00 00 <49> 8b 04 24 48 83 c3 01 8d 0c c5 08 00 00 00 01 cd 41 3b 5d 40 0f RSP: 0018:ffffd2670388f958 EFLAGS: 00010202 RAX: ffff8ba1065cc100 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000001 RSI: fffff266ffda7b90 RDI: ffffd2670388f9b0 RBP: 0000000000000010 R08: ffff8ba104e76000 R09: ffffd2670388fa50 R10: ffff8ba102dd42e0 R11: ffffffff9a908970 R12: 0000000000400010 R13: ffff8ba10a246400 R14: ffff8ba10a710220 R15: fffff266ffda7b90 FS: 00007fa3bc63f740(0000) GS:ffff8ba2e0f48000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000400010 CR3: 0000000107f9e003 CR4: 0000000000172ef0 Call Trace: <TASK> ? __tracing_map_insert+0x208/0x3a0 action_trace+0x67/0x70 event_hist_trigger+0x633/0x6d0 event_triggers_call+0x82/0x130 trace_event_buffer_commit+0x19d/0x250 trace_event_raw_event_sys_exit+0x62/0xb0 syscall_exit_work+0x9d/0x140 do_syscall_64+0x20a/0x2f0 ? trace_event_raw_event_sched_switch+0x12b/0x170 ? save_fpregs_to_fpstate+0x3e/0x90 ? _raw_spin_unlock+0xe/0x30 ? finish_task_switch.isra.0+0x97/0x2c0 ? __rseq_handle_notify_resume+0xad/0x4c0 ? __schedule+0x4b8/0xd00 ? restore_fpregs_from_fpstate+0x3c/0x90 ? switch_fpu_return+0x5b/0xe0 ? do_syscall_64+0x1ef/0x2f0 ? do_fault+0x2e9/0x540 ? __handle_mm_fault+0x7d1/0xf70 ? count_memcg_events+0x167/0x1d0 ? handle_mm_fault+0x1d7/0x2e0 ? do_user_addr_fault+0x2c3/0x7f0 entry_SYSCALL_64_after_hwframe+0x76/0x7e
The reason is that the stacktrace field is not labeled as such, and is treated as a normal field and not as a dynamic event that it is.
In trace_event_raw_event_synth() the event is field is still treated as a dynamic array, but the retrieval of the data is considered a normal field, and the reference is just the meta data:
// Meta data is retrieved instead of a dynamic array ---truncated---
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Analysis
by VulDB Data Team • 05/03/2026
The vulnerability described in CVE-2026-23088 resides within the Linux kernel's tracing subsystem, specifically in how synthetic events handle stacktrace fields. This issue manifests when a synthetic event is created based on another synthetic event that contains a stacktrace field, leading to a kernel crash upon enabling the event. The flaw occurs during the processing of trace events, particularly when the kernel attempts to handle a page fault while accessing memory at address 0x0000000000400010, indicating an invalid memory access pattern. The crash happens in the trace_event_raw_event_synth function, where the kernel incorrectly treats a stacktrace field as a regular field rather than recognizing it as a dynamic array element. This misclassification results in improper memory dereferencing, as the code attempts to retrieve meta data instead of the actual dynamic array content, triggering a supervisor read access error in kernel mode. The vulnerability is particularly concerning because it can be exploited through legitimate kernel tracing mechanisms, making it a potential vector for denial of service attacks or system instability.
The technical root cause of this vulnerability aligns with CWE-125: Out-of-bounds Read, where the kernel accesses memory beyond the intended bounds due to improper field type handling. The flaw stems from insufficient validation of field types within the synthetic event processing pipeline, causing the kernel to treat stacktrace fields as generic data fields instead of dynamic array references. This misclassification occurs in the trace_event_raw_event_synth function, where the kernel fails to properly identify that a field contains a stacktrace that should be handled as a dynamic array. The issue is further exacerbated by the lack of proper bounds checking when processing these fields, allowing the kernel to attempt memory access patterns that result in page faults. This vulnerability demonstrates a critical gap in kernel tracing subsystem validation logic, where field type information is not properly preserved or recognized during event processing, leading to memory corruption and system crashes.
The operational impact of this vulnerability extends beyond simple system instability, as it can compromise the reliability of kernel tracing operations that are essential for system monitoring and debugging. When triggered, the vulnerability causes immediate kernel crashes, effectively rendering the tracing subsystem unusable until the system is rebooted. This affects system administrators and security researchers who rely on kernel tracing for performance monitoring, debugging, and security analysis. The vulnerability is particularly dangerous in production environments where kernel tracing is actively used for system diagnostics, as it can cause unexpected system outages. The crash pattern observed in the kernel log shows a clear indication of memory corruption, with the error code indicating a not-present page fault that occurs during a supervisor read access. This type of vulnerability can also potentially be leveraged in more sophisticated attacks, as it demonstrates a fundamental flaw in how the kernel processes and validates synthetic event fields, possibly opening doors to privilege escalation or information disclosure scenarios.
Mitigation strategies for this vulnerability require immediate kernel updates from the Debian maintainers, as the fix has already been implemented in kernel version 6.16.3. System administrators should prioritize applying the patched kernel version to all affected systems to prevent exploitation. Additionally, organizations should implement monitoring for abnormal kernel crash patterns, particularly in systems where kernel tracing is actively used. The vulnerability highlights the importance of proper field type validation in kernel subsystems and suggests that enhanced input validation should be implemented for all synthetic event processing operations. Security teams should also consider disabling unnecessary kernel tracing features when they are not actively needed, reducing the attack surface. The fix addresses the core issue by ensuring that stacktrace fields are properly recognized as dynamic arrays during processing, preventing the incorrect memory access patterns that lead to page faults. Organizations should also review their kernel tracing configurations to identify and eliminate any synthetic event setups that might trigger similar conditions, particularly those involving nested synthetic events with stacktrace fields. This vulnerability serves as a reminder of the critical importance of thorough validation in kernel subsystems and the potential for seemingly benign tracing operations to expose critical security flaws.