CVE-2025-39793: io_uring/memmap: cast nr_pages to size_t before shifting

Severity: high (CVSS 7.8 v3.1)
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: 2025-09-12 · updated 2026-10-19

Description

In the Linux kernel, the following vulnerability has been resolved: io_uring/memmap: cast nr_pages to size_t before shifting If the allocated size exceeds UINT_MAX, then it's necessary to cast the mr->nr_pages value to size_t to prevent it from overflowing. In practice this isn't much of a concern as the required memory size will have been validated upfront, and accounted to the user. And > 4GB sizes will be necessary to make the lack of a cast a problem, which greatly exceeds normal user locked_vm settings that are generally in the kb to mb range. However, if root is used, then accounting isn't done, and then it's possible to hit this issue.

Affected products

Linux kernel: from 6.14 before 6.15.11; from 6.16 before 6.16.2 — fixed in 6.15.11, 6.16.2

How to fix

Upgrade to a fixed version: Linux kernel 6.15.11, 6.16.2. Check the vendor advisory for mitigations.

References

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