CVE-2026-89757
Low risk· EPSS 8%Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
In the Linux kernel, the mglru mechanism's sort_folio() function contained a buggy shortcut for folios that are no longer evictable but still on a generation list. The bug caused mlock_count to alias LIST_POISON2 (0x122, i.e. 290), leading to incorrect Mlocked accounting and folios remaining unevictable until freed. The shortcut also manipulated LRU flags in the wrong order, potentially causing unexpected behavior during concurrent folio isolation.
Risk Assessment
Organizations using Linux kernels with mglru may experience inflated Mlocked memory accounting and incorrect unevictable folio states, potentially leading to memory management errors and system stability issues. The bug can be user-visible through incorrect munlock behavior.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-89757, which isolates the affected folios as common folios and lets the generic shrink path cull them. If updating is not possible, consider disabling mglru as a temporary workaround.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: mm/mglru: fix and remove redundant unevictable folio handling sort_folio() has a shortcut for moving folios that are no longer evictable but are still sitting on a generation list. However, this shortcut is buggy. It does not follow the PG_lru usage convention, and it has a more serious issue. Unevictable folios are not threaded on lists[LRU_UNEVICTABLE], so that folio->lru can be reused to hold folio->mlock_count (see the comment in lruvec_init()). Hence lruvec_add_folio() skips the list_add() for them, and every other place that turns a folio unevictable initialises mlock_count explicitly: lru_add() sets it to 0, __mlock_folio() and __mlock_new_folio() set it to !!folio_test_mlocked(folio). sort_folio() sets nothing, and the lru_gen_del_folio() right above it may have already poisoned folio->lru via list_del(), so mlock_count ends up aliasing LIST_POISON2, which reads as 0x122, i.e. 290. The result is user visible. On munlock, __munlock_folio() decrements that bogus count, finds it still non-zero and bails out before clearing PG_mlocked, so the folio remains unevictable and the Mlocked accounting stays inflated until the folio is freed. The shortcut also touches the LRU flags in the wrong order. It calls lru_gen_del_folio() while PG_lru is still set, so a concurrent folio_test_clear_lru() (e.g. compaction, folio_isolate_lru()) can succeed on a folio that has already been taken off the generation list, which may lead to unexpected behavior. So fix it by isolating them as common folios and letting the generic shrink path cull them. This matches the classical LRU behavior, and there should be no visible effect on the generic eviction or isolation behavior. There is no performance concern either, such a folio goes through this once, and then it is off the generation lists for good.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS