CVE-2026-53189 in Linux
Summary
by MITRE • 06/25/2026
In the Linux kernel, the following vulnerability has been resolved:
mm/huge_memory: update file PMD counter before folio_put()
__split_huge_pmd_locked() updates the file/shmem RSS counter after dropping the PMD mapping's folio reference. If folio_put() drops the last reference, mm_counter_file() can later read freed folio state via folio_test_swapbacked().
Move the counter update before folio_put().
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Analysis
by VulDB Data Team • 06/25/2026
This vulnerability exists within the linux kernel's memory management subsystem particularly in how huge page memory handling operates. The issue resides in the mm/huge_memory module where the __split_huge_pmd_locked() function performs operations on page table entries that manage huge pages. When splitting huge pages into smaller ones, the kernel must properly account for memory usage statistics and maintain consistency between different memory accounting mechanisms.
The technical flaw occurs due to improper ordering of operations within the memory management code path. Specifically, when __split_huge_pmd_locked() processes a page table entry, it first removes the mapping reference by calling folio_put() which decrements the reference count and potentially frees the folio structure. Only after this operation does the function update the file or shared memory resident set size (RSS) counter through mm_counter_file(). This sequence creates a race condition where the counter update occurs after the folio structure may have been freed, leading to potential memory corruption or inconsistent accounting.
The operational impact of this vulnerability manifests as memory accounting inconsistencies that can lead to incorrect reporting of memory usage statistics and potentially affect memory management decisions made by the kernel. When folio_put() releases the last reference to a folio structure, the memory area becomes available for reuse or deallocation. However, if mm_counter_file() attempts to access the freed folio's state through folio_test_swapbacked(), it may encounter invalid memory contents or access freed memory locations. This can result in kernel panics, memory corruption, or incorrect accounting that affects system stability and resource management decisions.
This vulnerability aligns with CWE-129, which addresses improper validation of array indices, and CWE-476, concerning null pointer dereferences, as the code path accesses freed memory structures. The issue also relates to ATT&CK technique T1059 by potentially enabling privilege escalation through kernel memory corruption that could be exploited by malicious actors. The fix involves reordering the operations to ensure that memory accounting updates occur before releasing references to folio structures. This approach prevents the scenario where accounting code attempts to read freed memory while maintaining proper reference counting semantics.
The solution addresses fundamental memory management principles by ensuring proper ordering of operations in concurrent environments. Moving the counter update before folio_put() ensures that all necessary state information remains accessible during the accounting operation, preventing potential use-after-free conditions. This fix maintains the integrity of memory accounting mechanisms and prevents race conditions that could affect kernel stability. The change represents a standard defensive programming practice where resource management operations are ordered to prevent access to freed resources while maintaining proper synchronization between different kernel subsystems.
This vulnerability demonstrates the complexity of managing memory accounting in operating systems where multiple subsystems must maintain consistent views of memory usage statistics. The fix ensures that all memory management operations follow proper sequencing rules, preventing scenarios where one operation's cleanup affects another operation's ability to access required data structures. Such issues are particularly critical in kernel space where incorrect memory management can lead to system crashes or security vulnerabilities that undermine the entire operating system's integrity and reliability.