# CVE-2026-72380: xen/pvcalls: bound backend response req_id before indexing rsp[]

CVE-2026-72380 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-72380, released August 15, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-72380
- Priority: High
- CVSS: 8.8 (Moderate)
- EPSS: 0.0035
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 15, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-72380

## 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).

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-72380](https://patchblox.com/security/data/fix/linux/debian-cve-2026-72380.md) | Aug 15, 2026 |
| Linux | linux Debian 14 | 7.1.5-1 | [DEBIAN-CVE-2026-72380](https://patchblox.com/security/data/fix/linux/debian-cve-2026-72380.md) | Aug 15, 2026 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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