CVE-2026-90103 NFSv4.2: fix LAYOUTSTATS send buffer exhaustion
A malicious NFS server can cause a client-side kernel deadlock and denial of service by sending oversized LAYOUTSTATS responses that exhaust the send buffer.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90103?
CVE-2026-90103 is a high-severity denial of service 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:
NFSv4.2: fix LAYOUTSTATS send buffer exhaustion
encode_layoutstats_maxsz budgets XDR_QUADLEN(PNFS_LAYOUTSTATS_MAXSIZE), i.e. 256 bytes, for the layoutupdate4 body written by the layout driver. The flexfiles record can exceed that.
ff_layout_encode_ff_layoutupdate() emits, per data server, a netaddr4, an nfs_fh4, two ff_io_latency4, an nfstime4 and a bool. A data server whose filehandle is NFS_MAXFHSIZE bytes long already accounts for 132 of those bytes, and the two ff_io_latency4 at 64 bytes each, the nfstime4 and the bool add a further 144, so the body passes 256 bytes before the netaddr4 is encoded at all. encode_layoutstats() additionally writes the deviceid4 and the layoutupdate4 lou_type word, neither of which the macro accounts for.
The filehandle and the address are both chosen by the server, through LAYOUTGET and GETDEVICEINFO, so it can drive the encoder past the end of the send buffer. xdr_reserve_space() returns NULL once that happens, and the two ff_layout_encode_io_latency() calls run with dss_info->mirror->lock held, so a NULL return there leaves the lock permanently held.
Raise PNFS_LAYOUTSTATS_MAXSIZE to 384 so that the record fits inside the reservation.
Which versions are affected by CVE-2026-90103?
How do I fix CVE-2026-90103?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-90103 being exploited?
There is no known exploitation of CVE-2026-90103 in the wild and no public exploit code.
Sources
Also known as AZL-102644, BELL-CVE-2026-90103, DEBIAN-CVE-2026-90103, GHSA-qgw9-h34w-h93j, UBUNTU-CVE-2026-90103.