# CVE-2026-42493: Xen Project Denial of Service in x86 shadow paging

Source: https://junglewise.ai/threats/cve-2026-42493-xen-project-denial-of-service-in-x86-shadow-paging  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-28. Updated: 2026-07-28  
License: CC BY 4.0 with a link back

CVE-2026-42493 · Severity: info · Published 2026-07-28

A vulnerability in the Xen hypervisor's x86 shadow paging feature could allow a malicious user in a virtual machine to crash the entire physical host server. This component, which manages how virtual machines access memory, contains operations that can take too long to process, leading to a denial-of-service. Because fixing these issues is overly complex, the Xen Project has deprecated the feature and recommends using modern hardware-assisted alternatives.

Technologies: [Xen Project Xen](https://junglewise.ai/threats/technologies/xen). Vendors: [Xen Project](https://junglewise.ai/threats/vendors/xen-project).

## Quick answers

**Is CVE-2026-42493 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42493 being exploited in the wild.

**How severe is CVE-2026-42493?** Informational severity, published 28 July 2026.

**Which products and versions are affected?** Xen Project Xen All x86 versions with SHADOW_PAGING=y; versions prior to 4.7; 4.17.x; 4.18.x; 4.20.x; 4.21.x; 4.22.0.

**Is there a fix for CVE-2026-42493?** A patch was published on 2026-07-28. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42493 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-42493?** Check whether you run Xen Project Xen at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A denial-of-service vulnerability exists in Xen's x86 shadow paging implementation. Certain operations within the shadow paging code can take an excessively long time to complete and lack proper preemption points, allowing a guest VM to monopolize CPU resources or trigger host hangs. The Xen Project has determined that a full fix is too costly and has instead deprecated the functionality (XSA-495). The vulnerability affects all x86 systems where SHADOW_PAGING is enabled. Mitigation involves using Hardware Assisted Paging (HAP) for HVM/PVH guests, though no direct mitigation exists for PV guests other than disabling shadow paging support entirely in the hypervisor build.

## Affected products

- Xen Project Xen All x86 versions with SHADOW_PAGING=y; versions prior to 4.7; 4.17.x; 4.18.x; 4.20.x; 4.21.x; 4.22.0

## Timeline

- 2026-07-28: disclosed
- 2026-07-28: advisory: XSA-495 published
- 2026-07-28: patched

## References

- [https://xenbits.xenproject.org/xsa/advisory-495.html](https://xenbits.xenproject.org/xsa/advisory-495.html)

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