# CVE-2026-98366: RDMA/rxe: validate access flags before swapping the MR's PD

> A use-after-free vulnerability in the Linux kernel RDMA subsystem allows attackers to cause memory corruption and potential code execution via improper validation of access flags during memory region re-registration.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106164, BELL-CVE-2026-98366, DEBIAN-CVE-2026-98366, GHSA-rjh9-m2m4-jgrv, UBUNTU-CVE-2026-98366

## What is CVE-2026-98366?

CVE-2026-98366 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

RDMA/rxe: validate access flags before swapping the MR's PD

rxe_rereg_user_mr() reassigns mr->ibmr.pd first and only then
validates the IB_MR_REREG_ACCESS argument:

	if (flags & IB_MR_REREG_PD) {
		rxe_put(old_pd);
		rxe_get(pd);
		mr->ibmr.pd = ibpd;
	}

	if (flags & IB_MR_REREG_ACCESS) {
		if (access & ~RXE_ACCESS_SUPPORTED_MR)
			return ERR_PTR(-EOPNOTSUPP);
		mr->access = access;
	}

Both flags pass the entry check because RXE_MR_REREG_SUPPORTED is
IB_MR_REREG_PD | IB_MR_REREG_ACCESS, so a caller can reach the access
check with mr->ibmr.pd already reassigned.

mr->ibmr.pd is owned by the core, which adjusts pd->usecnt only on the
success path: ib_uverbs_rereg_mr() jumps to put_new_uobj on a driver error
without undoing the reassignment, so mr->pd == new_pd while the usecnts
still charge the MR to orig_pd. ib_dereg_mr_user() then decrements
new_pd, whose count can reach zero while a memory window still references
it; uverbs_free_pd() frees the PD on that count alone and rxe_mw_cleanup()
writes to freed memory:

  BUG: KASAN: slab-use-after-free in __rxe_put+0x31/0xa0
  Write of size 4 at addr ffff8881301dd690 by task rxe_poc/591
   __rxe_put+0x31/0xa0
   rxe_mw_cleanup+0x42/0x200
   __rxe_cleanup+0x115/0x370
   rxe_dealloc_mw+0x4c/0x80
  Allocated by task 591:
   ib_uverbs_alloc_pd+0x258/0x540
  Freed by task 591:
   ib_dealloc_pd_user+0x174/0x210
   uverbs_free_pd+0x8d/0xc0
   ib_uverbs_dealloc_pd+0x18e/0x1d0

Validate the access flags before mutating any state so the callback either
applies every requested change or none.

## Which versions are affected by CVE-2026-98366?


## How do I fix CVE-2026-98366?

Apply the vendor's patch.

## Is CVE-2026-98366 being exploited?

There is no known exploitation of CVE-2026-98366 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98366 and fix it if it is affected.

What it is: CVE-2026-98366 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98366 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98366/ (Markdown: https://insights.sbomify.com/CVE-2026-98366/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98366
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98366
- OSV: https://osv.dev/vulnerability/CVE-2026-98366

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98366/
Summaries are generated and may contain mistakes; the official description above is the record.