CVE-2026-89600
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A use-after-free vulnerability exists in the Linux kernel's fanotify subsystem regarding file range information. A pointer to the range position stored on the triggering task's stack is saved in a heap-allocated permission event, and when a signal interrupts the triggering task, the stack frame is unwound while the event reader still dereferences that pointer. This causes a stale stack value to be copied to userspace.
Risk Assessment
A local attacker could exploit this to leak stale kernel stack data or cause a kernel crash (panic), impacting confidentiality and availability. It was reported by KASAN as a use-after-free in fanotify_read.
Recommendation
Update the Linux kernel to a version containing the fix that stores the range position directly in the permission event and uses FANOTIFY_NO_RANGE when range information is unavailable.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: fanotify: fix use-after-free of file range info fsnotify_pre_content() builds its file_range on the triggering task's stack. fanotify_alloc_perm_event() saves a pointer to range.pos in the heap-allocated permission event so copy_range_info_to_user() can report the offset later. The event reader can set the event state to FAN_EVENT_REPORTED and then sleep while preparing the file descriptor. If a signal interrupts the triggering task at that point, fanotify_get_response() changes the state to FAN_EVENT_CANCELED and returns. This unwinds the file_range stack frame while the reader still owns the event. The reader then dereferences pevent->ppos and copies the stale stack value to userspace. KASAN reported: BUG: KASAN: use-after-free in fanotify_read+0x293e/0x2970 Read of size 8 at addr ffff88811434fc50 by task fanotify_inotif/95 Call Trace: fanotify_read+0x293e/0x2970 vfs_read+0x177/0xa20 ksys_read+0xf7/0x1c0 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f Store the range position directly in the permission event and use FANOTIFY_NO_RANGE when range information is unavailable. The event remains alive until the reader finishes, so the reported offset no longer depends on the triggering task's stack.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

