CVE-2026-98225
Low risk· EPSS 5%Exploitation Probability (EPSS)
Low risk5th percentile - higher than 5% of all known CVEs
Summary
A bug in the Linux kernel shrinker mechanism manifests when cgroup.memory=nokmem is enabled. In that configuration, shrinker_memcg_alloc() fails to allocate an id, leaving shrinker->id as zero, which is then mistakenly treated as a valid bit index. This triggers a WARN_ON_ONCE in set_shrinker_bit() when the first THP is queued in a cgroup.
Risk Assessment
The vulnerability only produces a kernel warning and does not lead to memory corruption or data loss, as the out-of-bounds read is prevented by WARN_ON_ONCE(). The risk to organizations is low — mainly log noise and potential confusion during troubleshooting.
Recommendation
Update the Linux kernel to a version containing the fix that clears shrinker->id before returning when cgroup.memory=nokmem is set. If updating is not possible, consider disabling cgroup.memory=nokmem or monitor logs for recurring warnings from mm/shrinker.c.
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- CVE-2026-99209Unknown
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- CVE-2026-99208Unknown
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: mm/shrinker: fix bogus set_shrinker_bit() with cgroup.memory=nokmem With cgroup.memory=nokmem, shrinker_memcg_alloc() bails out early and never allocates an id, so shrinker->id keeps the 0 it got from the kzalloc() in shrinker_alloc(). __list_lru_init() then copies that 0 into lru->shrinker_id, where it looks like a valid bit index. Nothing calls expand_shrinker_info() on nokmem either, so shrinker_nr_max stays 0 and every memcg ends up with an empty map (map_nr_max == 0). deferred_split_folio() hands a real memcg to __list_lru_add() regardless of whether the lru is memcg aware, so the first THP queued in a cgroup does set_shrinker_bit(memcg, nid, 0) and trips the bounds check: WARNING: mm/shrinker.c:212 at set_shrinker_bit+0x7d/0x90, CPU#126 Call Trace: <TASK> deferred_split_folio+0x18c/0x220 map_anon_folio_pmd_nopf+0xdd/0x130 map_anon_folio_pmd_pf+0x14/0xb0 do_huge_pmd_anonymous_page+0x1a1/0x620 __handle_mm_fault+0xea9/0x10d0 handle_mm_fault+0xe5/0x320 do_user_addr_fault+0x1cc/0x870 exc_page_fault+0x81/0x1b0 asm_exc_page_fault+0x27/0x30 </TASK> Harmless, the WARN_ON_ONCE() is what keeps the out of bounds unit[] read from happening, but the id should not look valid in the first place. Clear it before returning. Two other spots could paper over this: drop the id in __list_lru_init() when nokmem turns memcg_aware off, or make deferred_split_folio() pass NULL like list_lru_add_obj() does. Both leave shrinker->id lying around for the next caller, so fix it where the id is handed out.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

