Bug 2508029 (CVE-2026-62435)

Summary: CVE-2026-62435 xen: Xen: Grant table version switching race condition leads to incorrect resource handling
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Xen. When the Grant Table mechanism switches from version 1 to version 2, the number of valid grant references is reduced. A race condition can occur where code that temporarily releases and then re-acquires the grant table lock may make incorrect assumptions about the grant table's properties. This could lead to unexpected behavior or resource management issues within the system.
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Bug Depends On: 2508138    
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Description OSIDB Bzimport 2026-07-28 14:02:49 UTC 
[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]

With the introduction of Grant Table v2 came the requirement to be able to
switch between versions.  Switching from v1 to v2 reduces the number of
valid grant references, as a bigger shared entry structure is then needed
while the shared table doesn't change size.  Switching from v2 back to v1
the status frames, which are separate in v2, go away.

Code holding, but intermediately dropping and then re-acquiring the grant
table lock, sometimes wrongly assumes that said properties wouldn't change
across the window in time where the lock is not being held.

The v1 -> v2 issue is CVE-2026-62435.

The v2 -> v1 issue is CVE-2026-62436.