# CVE-2026-42487: Xen x86 HVM race condition in I/O port list traversal

Source: https://junglewise.ai/threats/cve-2026-42487-xen-x86-hvm-race-condition-in-i-o-port-list-traversal  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-18. Updated: 2026-06-20  
License: CC BY 4.0 with a link back

CVE-2026-42487 · Severity: high · CVSS 7.9 · Published 2026-06-18

A vulnerability exists in the Xen hypervisor, which is software used to run multiple virtual machines on a single physical server. A malicious or compromised virtual machine could trigger a crash of the entire physical host, leading to a total service outage for all other virtual machines on that server. In some cases, this could also lead to unauthorized access to data or increased privileges on the system.

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

## Quick answers

**Is CVE-2026-42487 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42487 being exploited in the wild.

**How severe is CVE-2026-42487?** High severity, with a CVSS score of 7.9, published 18 June 2026.

**Which products and versions are affected?** Xen Project Xen 3.2 and later (x86 only).

**Is there a fix for CVE-2026-42487?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-42487 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-42487?** 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 race condition (CWE-362) exists in the Xen hypervisor's handling of I/O port accesses for x86 HVM guests. I/O port translations are managed via linked lists that can be modified by the device model using XEN_DOMCTL_ioport_mapping. The hypervisor failed to properly synchronize list traversal with these updates. An attacker controlling a device model (such as one running in a stub domain or a de-privileged Dom0) can exploit this lack of synchronization to cause a hypervisor crash (DoS), or potentially achieve information disclosure or privilege escalation. The vulnerability affects x86 systems only; ARM systems and PV/PVH guests are not impacted. Patches are available for supported Xen versions.

## Affected products

- Xen Project Xen 3.2 and later (x86 only)

## Timeline

- 2026-06-09: disclosed: Initial public release of XSA-491
- 2026-06-18: advisory: NVD publication date

## References

- [https://xenbits.xenproject.org/xsa/advisory-491.html](https://xenbits.xenproject.org/xsa/advisory-491.html)
- [http://www.openwall.com/lists/oss-security/2026/06/09/11](http://www.openwall.com/lists/oss-security/2026/06/09/11)
- [http://xenbits.xen.org/xsa/advisory-491.html](http://xenbits.xen.org/xsa/advisory-491.html)

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