# CVE-2026-79603: Xen TLB flush race condition allowing stale page modification

Source: https://junglewise.ai/threats/cve-2026-79603-xen-tlb-flush-race-condition-allowing-stale-page-modification  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-08. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-79603 · Severity: medium · CVSS 4.3 · Published 2026-09-08

Xen is a virtualization platform that manages hardware resources for multiple guest operating systems. A race condition in x86 PV (paravirtual) guests allows a guest to modify memory pages that have been freed and logically scrubbed, potentially bypassing information isolation controls between guests. This undermines security deployments using silo-mode isolation with memory scrubbing.

## Quick answers

**Is CVE-2026-79603 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-79603 being exploited in the wild.

**How severe is CVE-2026-79603?** Medium severity, with a CVSS score of 4.3, published 8 September 2026.

**Which products and versions are affected?** Xen Xen 4.13 through 4.22.

**Is there a fix for CVE-2026-79603?** A patch was published on 2026-09-08: Patches released for Xen 4.18–4.22 and unstable branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-79603 attacked?** It is attacked with local access, in a hosted service.

**Am I affected by CVE-2026-79603?** Check whether anything you run is named in the advisory. 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

The vulnerability is a TLB (Translation Lookaside Buffer) flush race condition affecting x86 PV guests. When a guest frees memory pages, Xen defers TLB flushing until page re-use. However, the scrubbing of freed pages can occur before the delayed TLB flush, creating a window where a PV guest can modify already-scrubbed pages via stale TLB entries. This bypasses the isolation intended by `xsm=silo scrub-domheap` configurations. The vulnerability requires Xen 4.13 or later; exploitation is limited to x86 PV guests (not HVM or PVH). Patches are available for all affected versions (4.13 through 4.22).

## Affected products

- Xen Xen 4.13 through 4.22

## Timeline

- 2026-09-08: disclosed
- 2026-09-08: patched: Patches released for Xen 4.18–4.22 and unstable branch

## References

- [https://xenbits.xenproject.org/xsa/advisory-511.html](https://xenbits.xenproject.org/xsa/advisory-511.html)
- [http://www.openwall.com/lists/oss-security/2026/09/08/8](http://www.openwall.com/lists/oss-security/2026/09/08/8)