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CVE-2025-40348: slab: Avoid race on slab->obj_exts in alloc_slab_obj_exts

• Severity: unknown
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-12-16 · updated 2026-10-14

Description

In the Linux kernel, the following vulnerability has been resolved: slab: Avoid race on slab->obj_exts in alloc_slab_obj_exts If two competing threads enter alloc_slab_obj_exts() and one of them fails to allocate the object extension vector, it might override the valid slab->obj_exts allocated by the other thread with OBJEXTS_ALLOC_FAIL. This will cause the thread that lost this race and expects a valid pointer to dereference a NULL pointer later on. Update slab->obj_exts atomically using cmpxchg() to avoid slab->obj_exts overrides by racing threads. Thanks for Vlastimil and Suren's help with debugging.

Affected products

• Linux kernel: from 6.12.54 before 6.12.56; from 6.17.4 before 6.17.6 — fixed in 6.12.56, 6.17.6

How to fix

Upgrade to a fixed version: Linux kernel 6.12.56, 6.17.6. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/6ed8bfd24ce1cb31742b09a3eb557cd008533eec
• https://git.kernel.org/stable/c/7c34feda6a9a203c9744281f1b6671b7dad2012d
• https://git.kernel.org/stable/c/c7af5300d78460fc5037ddc77113ba3dbfe77dc0

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