CVE-2026-72380 xen/pvcalls: bound backend response req_id before indexing rsp[]
A malicious Xen backend can trigger an out-of-bounds write in the Linux kernel pvcalls frontend, potentially leading to code execution or denial of service.
- 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-2026-72380?
CVE-2026-72380 is a high-severity memory corruption vulnerability in Linux, published on 15 Aug 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:
xen/pvcalls: bound backend response req_id before indexing rsp[]
pvcalls_front_event_handler() takes req_id directly from the backend-supplied ring response and uses it to index the fixed-size bedata->rsp[] array for a memcpy() and a store, with no range check. A malicious or buggy backend can set req_id past PVCALLS_NR_RSP_PER_RING and drive an out-of-bounds write past the bedata allocation.
req_id was also declared int while the wire field rsp->req_id is u32, so a range check on the signed value alone is insufficient: a backend req_id of 0xffffffff becomes -1, passes a >= PVCALLS_NR_RSP_PER_RING test and indexes bedata->rsp[-1]. Declare req_id as u32 so a single bound covers both ends.
A backend that sends an out-of-range req_id has violated the wire protocol, so rather than silently dropping the response, log once and stop trusting the backend: set bedata->disabled. The event handler then ignores further responses, and the request paths that wait for a response return -EIO instead of blocking forever. This mirrors the fatal-error handling xen-netback uses (xenvif_fatal_tx_err()).
The pvcalls frontend currently trusts its backend, so this is not a classic-Xen security issue, but it matters for hardening PV frontends against malicious backends (confidential and disaggregated deployments).
Which versions are affected by CVE-2026-72380?
How do I fix CVE-2026-72380?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-72380 being exploited?
There is no known exploitation of CVE-2026-72380 in the wild and no public exploit code.
Sources
Also known as AZL-110423, BELL-CVE-2026-72380, DEBIAN-CVE-2026-72380, GHSA-44h4-v8mw-w74q, UBUNTU-CVE-2026-72380.