Guest-to-host privilege escalation via System Use underflow
Published Jul 28, 2026 · Updated Jul 28, 2026
Integer underflow in Xen libfsimage's ISO9660 System Use area in Xen 3.2 and later allows guest OS users to control the host. The ISO9660 directory parser calculates the System Use area length from attacker-controlled on-disk fields without validating them, allowing the length to wrap. Exploitation requires a guest configured to boot with pygrub; resulting memory corruption grants domain-construction-tool privileges, normally host control.
Summary
What happened
Integer underflow in Xen libfsimage's ISO9660 System Use area in Xen 3.2 and later allows guest OS users to control the host. The ISO9660 directory parser calculates the System Use area length from attacker-controlled on-disk fields without validating them, allowing the length to wrap. Exploitation requires a guest configured to boot with pygrub; resulting memory corruption grants domain-construction-tool privileges, normally host control.
The record
- CVE
- CVE-2026-42495
- Published
- Jul 28, 2026
- Updated
- Jul 28, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-191, T1611
- Attack vector
- local
- Privileges
- Unavailable
Timeline
How it unfolded
- Jul 28, 2026CVE publishedPublication date reported by the CVE source.
- Jul 28, 2026Record updatedLatest update available in the CVE record.
Exploitability
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What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
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Attacks
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Public exploit references
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Technologies
Your stack
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Your stack
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