CVE-2026-72380
Received Received - Intake

Out-of-Bounds Write in Linux Kernel Xen PVCalls Frontend

Publication date: 2026-08-15

Last updated on: 2026-08-15

Assigner: kernel.org

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).

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Meta Information

Published
2026-08-15
Last Modified
2026-08-15
Generated
2026-08-15
AI Q&A
2026-08-15
EPSS Evaluated
N/A
NVD
CVE-2026-72380
EUVD
EUVD-2026-59279

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux_kernel linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a vulnerability in the Linux kernel's Xen PV Calls subsystem. A malicious or buggy backend can send a crafted response with an out-of-bounds req_id value, causing the frontend to write beyond the allocated memory array. The issue stems from insufficient validation of the req_id field, which is signed but should be unsigned, allowing negative values to bypass checks.

Detection Guidance

This vulnerability is specific to the Linux kernel's pvcalls frontend and requires access to the system running the vulnerable kernel. Detection involves checking kernel logs for errors related to pvcalls or backend responses. Commands like dmesg | grep pvcalls or journalctl -k | grep pvcalls may help identify issues. Ensure your kernel version is checked against the patched version.

Impact Analysis

If exploited, this flaw could lead to memory corruption, crashes, or potential code execution on the affected system. It primarily affects systems using Xen's PV Calls frontend with untrusted backends, such as in confidential or disaggregated deployments.

Mitigation Strategies

Update the Linux kernel to the latest patched version that resolves this issue. If updating is not immediately possible, disable the pvcalls frontend module by running rmmod pvcalls_front or blacklisting the module in your configuration. Monitor system logs for any signs of exploitation or misbehaving backends.

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