CVE-2026-98361 RDMA/rxe: Restore HMM_PFN_WRITE check in ODP write paths
An unprivileged user can overwrite read-only file pages via RDMA ODP, enabling privilege escalation by modifying sensitive files like setuid binaries.
- 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
What is CVE-2026-98361?
CVE-2026-98361 is a high-severity 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: Restore HMM_PFN_WRITE check in ODP write paths
Commit 0b261d7c1cd3 ("RDMA/rxe: Break endless pagefault loop for RO pages") dropped the access permission test from rxe_check_pagefault() and left only HMM_PFN_VALID. A page faulted in read-only, for example a page-cache folio behind a PROT_READ file mapping, then satisfies the check and ODP write operations (RDMA WRITE, RDMA READ response, SEND payload, atomics) modify it through kmap without ever breaking CoW.
An unprivileged user can register an ODP MR over such a mapping and have incoming RDMA traffic overwrite the page cache of a file it only holds O_RDONLY, including /etc/passwd or setuid binaries. This is the same primitive class as Dirty COW and CVE-2022-2590.
mlx5 has the missing invariant: its ODP path sets the device write bit only for pfns that carry HMM_PFN_WRITE. Restore it in rxe by requiring HMM_PFN_WRITE in rxe_check_pagefault() for every operation except RXE_PAGEFAULT_RDONLY. A write to a non-writable VMA now fails the one fault attempt with -EPERM from hmm_vma_fault() instead of re-faulting forever. For a writable VMA the fault breaks CoW and the write lands in the private page.
Keep pmem flushes on the read-only check. arch_wb_cache_pmem() never modifies memory, and the FLUSH access bits do not make the umem writable, so classifying flushes as writes would make every flush against a flush-only MR fail.
Which versions are affected by CVE-2026-98361?
How do I fix CVE-2026-98361?
Apply the vendor's patch.
Is CVE-2026-98361 being exploited?
There is no known exploitation of CVE-2026-98361 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98361, DEBIAN-CVE-2026-98361, GHSA-g3wm-757g-9p35, UBUNTU-CVE-2026-98361.