CVE-2026-64251 in Linux
Summary
by MITRE • 07/24/2026
In the Linux kernel, the following vulnerability has been resolved:
pwrseq: core: fix use-after-free in pwrseq_debugfs_seq_next()
pwrseq_debugfs_seq_next() declares 'next' with __free(put_device), which causes put_device() to be called on the returned pointer when the variable goes out of scope. This results in a use-after-free since the seq_file framework receives a pointer whose reference has already been dropped.
Simply removing __free(put_device) would fix the UAF but would leak the reference acquired by bus_find_next_device(), as stop() only calls up_read(&pwrseq_sem) and never releases the device reference.
Fix this by making the reference counting consistent across all seq_file callbacks, matching the standard pattern used by PCI and SCSI:
- start(): use get_device() so it returns a referenced pointer. - next(): explicitly put_device(curr) to release the previous device's reference (no NULL check needed - the seq_file framework only calls next() while the previous return was non-NULL). - stop(): put_device(data) to release the last iterated device's reference, with a NULL guard since stop() may be called with NULL when start() returned NULL or next() reached end-of-sequence.
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Analysis
by VulDB Data Team • 07/24/2026
The vulnerability described represents a critical use-after-free condition within the Linux kernel's power sequence subsystem, specifically affecting the pwrseq_debugfs_seq_next() function. This flaw exists in the core power sequence management framework that handles device power state transitions and is particularly concerning because it operates within the debugfs interface which provides kernel developers and system administrators with access to internal kernel data structures. The issue manifests when the seq_file framework attempts to iterate through power sequence devices, creating a scenario where memory corruption can occur due to improper reference counting mechanisms.
The technical root cause stems from incorrect memory management annotations in the function declaration where the variable 'next' is marked with __free(put_device) attribute. This annotation instructs the compiler to automatically call put_device() on the returned pointer when it goes out of scope, effectively dereferencing a pointer that has already been released by the seq_file framework. The sequence file iteration mechanism expects to receive valid device pointers that remain accessible throughout the iteration process, but the improper cleanup causes the kernel to access freed memory locations, potentially leading to arbitrary code execution or system crashes.
This vulnerability directly maps to CWE-416, which describes the use of freed memory condition, and represents a classic example of improper resource management in kernel space. The attack surface is particularly significant as debugfs interfaces are commonly accessible to userspace applications during system troubleshooting and development activities. The operational impact includes potential system instability, denial of service conditions, and in worst-case scenarios, privilege escalation opportunities that could allow malicious actors to gain unauthorized access to kernel memory spaces.
The mitigation strategy implemented follows well-established patterns from similar subsystems within the Linux kernel, particularly those used in PCI and SCSI drivers where consistent reference counting practices have been proven effective. The solution requires modifications across all seq_file callback functions to maintain proper device reference management throughout the iteration lifecycle. The start() function now properly calls get_device() to acquire an additional reference count before returning a device pointer, ensuring the memory remains allocated during iteration. The next() function explicitly releases the previous device's reference using put_device() without null checks since the framework guarantees non-null inputs, and the stop() function safely releases the final reference with proper null guards to handle edge cases where iteration may terminate prematurely or start() fails.
This fix aligns with ATT&CK technique T1068 by addressing kernel-level privilege escalation vectors through memory corruption vulnerabilities. The implementation demonstrates adherence to kernel security best practices by ensuring consistent reference counting patterns across all iterator callbacks, preventing both use-after-free conditions and resource leaks that could accumulate over time. The approach taken maintains backward compatibility while strengthening the overall security posture of the power sequence subsystem against common exploitation techniques targeting kernel memory management flaws.