CVE-2026-93781 scsi: core: Do not block on tag allocation in scsi_eh_lock_door()

What is CVE-2026-93781?

CVE-2026-93781 is a denial of service vulnerability in Linux, published on 24 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:

scsi: core: Do not block on tag allocation in scsi_eh_lock_door()

scsi_eh_lock_door() is called from scsi_restart_operations() while the host is still in the SHOST_RECOVERY state, i.e. before the host is switched back to SHOST_RUNNING and scsi_run_host_queues() restarts the queues. It allocates a request via scsi_alloc_request() with no flags, so blk_mq_get_tag() may block waiting for a free sched tag when all tags are already in use.

Those tags can be held by commands that were just requeued by scsi_eh_flush_done_q() during error handling. Such commands cannot be dispatched until the host leaves SHOST_RECOVERY and scsi_run_host_queues() is called - which only happens *after* scsi_eh_lock_door() returns.

This forms a circular dependency:

- scsi_eh_lock_door(), running in the SCSI error handler thread, waits for a sched tag held by a requeued command;

- the requeued command cannot complete and release its sched tag until the error handler thread leaves scsi_restart_operations() and restart the queues.

For devices with a single driver tag (e.g. USB storage) it is a guaranteed deadlock and I/O that can never be submitted. This problem has also been reproduced in our environment.

Locking the door is a best-effort operation, and scsi_eh_lock_door() already returns silently when the request allocation fails. Pass BLK_MQ_REQ_NOWAIT to scsi_alloc_request() so the allocation fails instead of blocking when no tag is available. This breaks the circular dependency and allows the error handler to finish restarting the queues, after which the pending commands are dispatched normally.

Which versions are affected by CVE-2026-93781?

How do I fix CVE-2026-93781?

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-2026-93781 being exploited?

There is no known exploitation of CVE-2026-93781 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-103550, BELL-CVE-2026-93781, DEBIAN-CVE-2026-93781, GHSA-3mhv-m8g9-8q53, UBUNTU-CVE-2026-93781.