CVE-2026-23225

CVE-2026-23225 is a high-severity vulnerability with a CVSS 3.x base score of 7.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Description

In the Linux kernel, the following vulnerability has been resolved: sched/mmcid: Don't assume CID is CPU owned on mode switch Shinichiro reported a KASAN UAF, which is actually an out of bounds access in the MMCID management code. CPU0 CPU1 T1 runs in userspace T0: fork(T4) -> Switch to per CPU CID mode fixup() set MM_CID_TRANSIT on T1/CPU1 T4 exit() T3 exit() T2 exit() T1 exit() switch to per task mode ---> Out of bounds access. As T1 has not scheduled after T0 set the TRANSIT bit, it exits with the TRANSIT bit set. sched_mm_cid_remove_user() clears the TRANSIT bit in the task and drops the CID, but it does not touch the per CPU storage. That's functionally correct because a CID is only owned by the CPU when the ONCPU bit is set, which is mutually exclusive with the TRANSIT flag. Now sched_mm_cid_exit() assumes that the CID is CPU owned because the prior mode was per CPU. It invokes mm_drop_cid_on_cpu() which clears the not set ONCPU bit and then invokes clear_bit() with an insanely large bit number because TRANSIT is set (bit 29). Prevent that by actually validating that the CID is CPU owned in mm_drop_cid_on_cpu().

Frequently asked questions

What is CVE-2026-23225?
In the Linux kernel, the following vulnerability has been resolved: sched/mmcid: Don't assume CID is CPU owned on mode switch Shinichiro reported a KASAN UAF, which is actually an out of bounds access in the MMCID management code. CPU0 CPU1 T1 runs in userspace T0: fork(T4) -> Switch to per CPU CID mode fixup() set MM_CID_TRANSIT on T1/CPU1 T4 exit() T3 exit() T2 exit() T1 exit() switch to per task mode ---> Out of bounds access. As T1 has not scheduled after T0 set the TRANSIT bit, it exits with the TRANSIT bit set. sched_mm_cid_remove_user() clears the TRANSIT bit in the task and drops the CID, but it does not touch the per CPU storage. That's functionally correct because a CID is only owned by the CPU when the ONCPU bit is set, which is mutually exclusive with the TRANSIT flag. Now sched_mm_cid_exit() assumes that the CID is CPU owned because the prior mode was per CPU. It invokes mm_drop_cid_on_cpu() which clears the not set ONCPU bit and then invokes clear_bit() with an insanely large bit number because TRANSIT is set (bit 29). Prevent that by actually validating that the CID is CPU owned in mm_drop_cid_on_cpu().
How severe is CVE-2026-23225?
CVE-2026-23225 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-23225 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (2nd percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-23225?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-23225 have an EU (EUVD) identifier?
Yes. CVE-2026-23225 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7676.
When was CVE-2026-23225 published?
CVE-2026-23225 was published on 2026-02-18 and last updated on 2026-06-17.

References