CVE-2026-64216 in Linux
Summary
by MITRE • 07/24/2026
In the Linux kernel, the following vulnerability has been resolved:
netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages()
netfs_unlock_abandoned_read_pages(rreq) accesses the index of the folios it is wanting to unlock and compares that to rreq->no_unlock_folio so that it doesn't unlock a folio being read for netfs_perform_write() or netfs_write_begin().
However, given that netfs_unlock_abandoned_read_pages() is called _after_ NETFS_RREQ_IN_PROGRESS is cleared, the one folio that it's not allowed to dereference is the one specified by ->no_unlock_folio as ownership immediately reverts to the caller.
Fix this by storing the folio pointer instead and using that rather than the index. Also fix netfs_unlock_read_folio() where the same applies.
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Analysis
by VulDB Data Team • 07/24/2026
This vulnerability represents a use-after-free condition in the Linux kernel's network filesystem implementation, specifically within the netfs subsystem that handles remote file operations. The issue occurs in the netfs_unlock_abandoned_read_pages function where improper handling of folio indices creates a potential race condition that could lead to memory corruption. The vulnerability stems from accessing folio indices after the NETFS_RREQ_IN_PROGRESS flag has been cleared, which can result in dereferencing freed memory when attempting to unlock folios that are no longer valid.
The technical flaw arises from the improper management of folio references within the network filesystem locking mechanism. When netfs_unlock_abandoned_read_pages processes folios for unlocking, it relies on index-based access rather than direct pointer references to determine which folios should be skipped. This approach becomes problematic because the function is invoked after NETFS_RREQ_IN_PROGRESS is cleared, meaning that the folio indices may no longer correspond to valid memory locations. The specific condition involves comparing folio indices against rreq->no_unlock_folio, but this comparison fails to account for the fact that the folio being referenced by no_unlock_folio has already been returned to the caller's ownership and could be freed.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling privilege escalation or system instability in network filesystem operations. Attackers could exploit this condition to manipulate memory layout during concurrent read operations, particularly when dealing with network-based file systems that rely heavily on asynchronous I/O operations. The vulnerability affects the core kernel networking subsystem and could compromise the integrity of remote file access mechanisms, making it particularly dangerous for server environments that depend extensively on network filesystems such as NFS or CIFS implementations.
The fix implements a critical design change by replacing index-based folio access with direct pointer storage within both netfs_unlock_abandoned_read_pages and netfs_unlock_read_folio functions. This modification ensures that the actual folio objects remain accessible even after the request state has changed, eliminating the race condition that led to the use-after-free scenario. The solution aligns with established security practices for managing object lifetimes in concurrent systems and addresses a fundamental flaw in kernel memory management patterns. This approach prevents the scenario where freed folio structures could be accessed through stale index references, thus maintaining system stability and preventing potential exploitation vectors.
This vulnerability demonstrates the complexity of race condition management in kernel space operations and highlights the importance of proper object lifecycle management in concurrent environments. The fix directly addresses CWE-416, which covers use-after-free vulnerabilities, and aligns with ATT&CK techniques related to privilege escalation through kernel memory corruption. The remediation approach emphasizes defensive programming practices that prevent memory safety issues in high-concurrency kernel subsystems, particularly those handling asynchronous file operations across network boundaries.