CVE-2025-39816: io_uring/kbuf: always use READ_ONCE() to read ring provided buffer lengths

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-09-16 · updated 2026-10-19

Description

In the Linux kernel, the following vulnerability has been resolved: io_uring/kbuf: always use READ_ONCE() to read ring provided buffer lengths Since the buffers are mapped from userspace, it is prudent to use READ_ONCE() to read the value into a local variable, and use that for any other actions taken. Having a stable read of the buffer length avoids worrying about it changing after checking, or being read multiple times. Similarly, the buffer may well change in between it being picked and being committed. Ensure the looping for incremental ring buffer commit stops if it hits a zero sized buffer, as no further progress can be made at that point.

Affected products

Linux kernel: from 6.12 before 6.12.49; from 6.13 before 6.16.5; 6.17-rc1, 6.17-rc2, 6.17-rc3 — fixed in 6.12.49, 6.16.5

How to fix

Upgrade to a fixed version: Linux kernel 6.12.49, 6.16.5. Check the vendor advisory for mitigations.

References

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