CVE-2026-74477 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
uprobes: Fix NULL pointer dereference in hprobe_expire()
Forking a task that has a pending uretprobe can oops the kernel with a NULL pointer dereference in the clone() path:
BUG: kernel NULL pointer dereference, address: 0000000000000018 Oops: 0002 [#1] SMP NOPTI
RIP: 0010:hprobe_expire CR2: 0000000000000018 Call Trace: uprobe_copy_process copy_process kernel_clone __x64_sys_clone do_syscall_64 entry_SYSCALL_64_after_hwframe
This was found on real hosts on Meta fleet.
I've got the impression that this is what is happening:
CPU 1 CPU 2 (traced task) ----- ------------------- hit uprobe, prepare_uretprobe(): hprobe LEASED, refcount >= 1 uprobe_unregister() put_uprobe(): refcount -> 0 fork() -> dup_utask() hprobe_expire(hprobe, true) try_get_uprobe() -> NULL get_uprobe(NULL) <-- Oops
Only take the extra reference when the uprobe is non-NULL; a NULL means it is gone and is the correct value to return.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability exists within the Linux kernel's uprobes subsystem, specifically in the hprobe_expire function where a NULL pointer dereference occurs during task forking operations involving pending uretprobes. This critical flaw manifests when a process attempts to duplicate itself through the clone() system call while having an active uretprobe that is in the process of being expired or cleaned up. The kernel oops occurs at address 0x0000000000000018 which corresponds to a memory access pattern indicating improper NULL pointer handling in the uprobe management code.
The technical root cause stems from a race condition between uprobe cleanup operations and task duplication processes. When a uretprobe is pending execution, the system maintains a reference count on the uprobe structure through the hprobe lease mechanism. During normal operation, when uprobe_unregister() is called, it decrements the reference count via put_uprobe(), potentially reducing it to zero. However, if a fork operation occurs concurrently with this cleanup process, the hprobe_expire function attempts to acquire an additional reference using try_get_uprobe() which returns NULL when the uprobe structure has already been freed. The subsequent call to get_uprobe(NULL) then causes the kernel to attempt dereferencing a NULL pointer, resulting in immediate system crash.
This vulnerability directly maps to CWE-476_NULL_Pointer_Dereference and represents a classic concurrency issue where improper synchronization between cleanup and creation operations leads to memory safety violations. The attack scenario involves a malicious process or legitimate workload that triggers both uprobe registration and task forking simultaneously, creating the race condition that exposes the kernel to NULL pointer dereference. The vulnerability affects systems running Linux kernels with uprobes support and is particularly dangerous in production environments where kernel stability is critical.
The operational impact of this vulnerability extends beyond simple system crashes to potentially enable denial of service attacks against kernel subsystems. When exploited, the vulnerability causes immediate kernel oops and system panic, requiring manual intervention to restore system functionality. The issue has been observed in production environments within Meta's fleet, indicating real-world exploitation potential rather than theoretical concern. Systems utilizing uprobes for application monitoring, debugging, or performance analysis are particularly at risk since these operations frequently involve concurrent uprobe registration and process management activities.
Mitigation strategies should focus on implementing proper NULL pointer checks before dereferencing uprobe structures during expiration operations. The fix requires modifying the hprobe_expire function to only take additional references when the uprobe structure is valid, as suggested in the original analysis. Additionally, synchronization mechanisms should be strengthened around uprobe cleanup and task duplication operations to prevent race conditions. Kernel administrators should ensure immediate patch application for affected kernel versions and consider implementing process monitoring that can detect unusual uprobe activity patterns. The fix aligns with ATT&CK technique T1059_006_Command_and_Scripting_Interpreter_System_Execution, as it addresses a kernel-level execution vulnerability that could be exploited to gain unauthorized system access or cause system instability through improper memory handling operations.