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Xen: Stale TLB Entry Ahead of Page Scrubbing (XSA-511)

medium Nessus Plugin ID 344803

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Synopsis

The remote Xen hypervisor installation is missing a security update.

Description

x86 PV guests can free memory pages while still keeping a stale TLB entry pointing to them. A TLB flush is only issued by Xen (if needed) when the page is re-used. Since it's possible for the page to be scrubbed ahead of the TLB flush, there's a window where a PV guest can modify an already scrubbed page.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Apply the appropriate patch according to the vendor advisory.

See Also

https://xenbits.xenproject.org/xsa/advisory-511.html

Plugin Details

Severity: Medium

ID: 344803

File Name: xen_server_XSA-511.nasl

Version: 1.1

Type: Local

Family: Misc.

Published: 9/11/2026

Updated: 9/11/2026

Configuration: Enable paranoid mode

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Low

Score: 1.2

Percentile: 0.01

CVSS v2

Risk Factor: Medium

Base Score: 4

Vector: CVSS2#AV:N/AC:L/Au:S/C:P/I:N/A:N

CVSS Score Source: CVE-2026-79603

CVSS v3

Risk Factor: Medium

Base Score: 4.3

Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Vulnerability Information

CPE: cpe:/o:xen:xen

Required KB Items: Settings/ParanoidReport, installed_sw/Xen Hypervisor

Patch Publication Date: 9/8/2026

Vulnerability Publication Date: 9/8/2026

Reference Information

CVE: CVE-2026-79603

IAVB: 2026-B-0250