Bug 2559183

Summary: CVE-2026-79609 xen: Xen: Denial of Service via guest page table access beyond direct memory mapping [fedora-all]
Product: [Fedora] Fedora Reporter: Oleg Sushchenko <osushche>
Component: xenAssignee: Michael Young <m.a.young>
Status: ON_QA --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: medium Docs Contact:
Priority: medium    
Version: rawhideCC: jforbes, m.a.young
Target Milestone: ---Keywords: Security, SecurityTracking
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Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["a862a8f7-f600-4583-8f29-224040ef9af7"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On:    
Bug Blocks: 2550647    

Description Oleg Sushchenko 2026-10-22 17:28:03 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

XPTI (Xen Page Table Isolation) was introduced to mitigate Meltdown
(CVE-2017-5754, one aspect of XSA-254).  This involves copying 64-bit PV
guest page table entries from guest-chosen root page tables to the Xen-
chosen one which is in actual use by hardware.  To read the guest root
page table, the directmap is used.  PV guests, however, have a directmap
which may not cover all memory; in particular this is the case if any
memory extends beyond the 5 TiB (CONFIG_BIGMEM=y: 3.5 TiB) address
boundary.
Comment 1 Fedora Update System 2026-10-30 23:27:44 UTC 
FEDORA-2026-2b73a60d2c (xen-4.20.4-4.fc43) has been submitted as an update to Fedora 43.
https://bodhi.fedoraproject.org/updates/FEDORA-2026-2b73a60d2c
Comment 2 Fedora Update System 2026-10-31 02:44:25 UTC 
FEDORA-2026-2b73a60d2c has been pushed to the Fedora 43 testing repository.
Soon you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2026-2b73a60d2c`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2026-2b73a60d2c

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.