VDB
CVE-2026-23553
CVE-2026-23553
PUBLISHED
CVSS 2.9000000953674316 LOW
In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider: 1) vCPU runs on CPU A, running task 1. 2) vCPU moves to CPU B, idle gets scheduled on A. Xen skips IBPB. 3) On CPU B, guest kernel switches from task 1 to 2, issuing IBPB. 4) vCPU moves back to CPU A. Xen skips IBPB again. Now, task 2 is running on CPU A with task 1's training still in the BTB.
EPSS 0.03% · 10.0th percentile
Risk Scores
CVSS v3.1
2.9000000953674316
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
EPSS Score
0.03%
10.0th percentile
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| xen | xen | 4.6.0, 4.6.0 |
| Citrix | XenServer | |
| Xen | Xen | consult Xen advisory XSA-479, consult Xen advisory XSA-479 |
| XEN | Xen |
Timeline
- Jan 27, 2026 CVE Published
- Jan 27, 2026 PoC Published
- Jan 27, 2026 PoC Published
- Jan 27, 2026 PoC Published
- Jan 27, 2026 PoC Published
- Jan 28, 2026 PoC Published
- Jan 29, 2026 EPSS Score
- Jan 30, 2026 CVE Updated
- Jan 30, 2026 PoC Published
- Jan 31, 2026 EPSS Score
- Feb 3, 2026 EPSS Score
- Feb 5, 2026 EPSS Score
References
- https://xenbits.xenproject.org/xsa/advisory-479.html url
- http://www.openwall.com/lists/oss-security/2026/01/27/3 url
- http://xenbits.xen.org/xsa/advisory-479.html url
- https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX695997&articleURL=XenServer_Security_Update_for_CVE_2025_58151_and_CVE_2026_23553 advisory
- https://xenbits.xen.org/xsa/advisory-477.html advisory
- https://xenbits.xen.org/xsa/advisory-478.html advisory
- https://xenbits.xen.org/xsa/advisory-479.html advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-23553 advisory