CVE-2026-90149 NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers
A NULL pointer dereference in the Linux kernel NFSv4 flexfiles module causes a system crash when interacting with NFSv4.0 data servers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90149?
CVE-2026-90149 is a high-severity vulnerability in Linux, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
NFSv4/flexfiles: fix NULL dereference for NFSv4.0 data servers
flexfiles accepts NFSv4.0 data servers, but two NFSv4 code paths assume the data server client has a session. Unlike NFSv4.1+, an NFSv4.0 client has no session (clp->cl_session is NULL; it uses clp->cl_slot_tbl), so I/O to a v4.0 flexfiles DS oopses:
- nfs4_init_ds_session() dereferences clp->cl_session->session_state while seeding the DS lease. It also only seeds cl_lease_time when NFS4_SESSION_INITING is set; without a session that never happens, so cl_lease_time stays 0 and nfs4_renew_state() busy-loops, requeuing every 5 seconds. Seed the lease whenever there is no session and return before touching session state.
- ff_layout_async_handle_error_v4() dereferences clp->cl_session->fc_slot_table on every DS I/O error. Fall back to the v4.0 transport slot table (clp->cl_slot_tbl) when there is no session.
Which versions are affected by CVE-2026-90149?
How do I fix CVE-2026-90149?
Apply the vendor's patch.
Is CVE-2026-90149 being exploited?
There is no known exploitation of CVE-2026-90149 in the wild and no public exploit code.
Sources
Also known as AZL-102438, BELL-CVE-2026-90149, DEBIAN-CVE-2026-90149, GHSA-5pv5-p9q3-rvv6, UBUNTU-CVE-2026-90149.