CVE-2026-72380
HighCVSS 8.8Exploitation Probability (EPSS)
Low risk21th percentile - higher than 21% of all known CVEs
Summary
In the Linux kernel's xen/pvcalls driver, the request ID (req_id) from the backend is not validated before being used as an index into the rsp[] array. A malicious or buggy backend can set req_id out of bounds, leading to an out-of-bounds write. Additionally, the int type for req_id does not cover u32 values, allowing negative indexing.
Risk Assessment
An attacker controlling the backend could cause memory corruption in the kernel, potentially leading to privilege escalation or system crash. The vulnerability affects Xen paravirtualization environments, especially with untrusted backends.
Recommendation
Apply the kernel patch that adds validation of req_id as u32 and disables the backend on protocol violation. Update your system to a kernel version containing this fix.
Original NVD description (English source)
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).