CVE-2026-90266 btrfs: zoned: don't force read-only on transient -EAGAIN from reloc merge
A local attacker can cause a denial of service on zoned Btrfs filesystems by triggering transient errors during reclaim, aborting transactions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90266?
CVE-2026-90266 is a denial of service vulnerability in Linux, published on 17 Sep 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:
btrfs: zoned: don't force read-only on transient -EAGAIN from reloc merge
On a zoned FS, btrfs_delayed_refs_rsv_refill() returns -EAGAIN whenever the over-committed metadata plus the zone_unusable bytes exceeds the usable size in a metadata block-group to avoid heavy over-commit of metadata and early ENOSPC in one transaction.
If this happens while doing reclaim, the transaction is getting aborted.
Treat -EAGAIN as a soft, retryable condition in case of block-group reclaim.
Which versions are affected by CVE-2026-90266?
How do I fix CVE-2026-90266?
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-2026-90266 being exploited?
There is no known exploitation of CVE-2026-90266 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-90266, GHSA-gj86-9624-3gxh, UBUNTU-CVE-2026-90266.