CVE-2026-93186 cxl/mbox: Clamp mailbox output allocation to the payload size
A local attacker can trigger a kernel panic or denial of service by requesting an excessively large mailbox output allocation in the CXL memory driver.
- 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-2026-93186?
CVE-2026-93186 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:
cxl/mbox: Clamp mailbox output allocation to the payload size
CXL_MEM_SEND_COMMAND bounds the user's in.size to the mailbox payload size but leaves out.size unbounded, then cxl_mbox_cmd_ctor() calls kvzalloc(out.size). A large out.size drives a huge allocation, above INT_MAX it WARNs and taints, and with panic_on_warn=1 it panics.
The transport __cxl_pci_mbox_send_cmd() already clamps the response copy to min(out.size, payload_size, device len), so the output buffer is never written beyond payload_size. Clamp the allocation to payload_size too, matching the RAW path.
Which versions are affected by CVE-2026-93186?
How do I fix CVE-2026-93186?
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-2026-93186 being exploited?
There is no known exploitation of CVE-2026-93186 in the wild and no public exploit code.
Sources
Also known as AZL-102953, BELL-CVE-2026-93186, DEBIAN-CVE-2026-93186, GHSA-4xf9-vh86-48mc, UBUNTU-CVE-2026-93186.