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CVE-2015-8553 Xen Project CVE debrief

CVE-2015-8553 is a medium-severity information disclosure vulnerability in Xen hypervisor environments. The flaw allows guest OS users to read sensitive information from uninitialized locations in host OS kernel memory. This occurs when memory and I/O decoding control bits are not properly enabled. The vulnerability represents an incomplete fix for CVE-2015-0777, indicating a regression where the original remediation did not fully address the underlying security gap. The issue affects confidentiality with high impact (C:H) while requiring local access and low attack complexity.

Vendor
Xen Project
Product
Xen hypervisor
CVSS
MEDIUM 6.5
CISA KEV
Not listed in stored evidence
Original CVE published
2016-04-13
Original CVE updated
2026-05-26
Advisory published
2016-04-13
Advisory updated
2026-05-26

Who should care

Organizations running Xen-based virtualization infrastructure, particularly those hosting multi-tenant or untrusted guest workloads. System administrators responsible for hypervisor security patching and PCI passthrough configurations. Security teams tracking incomplete vulnerability fixes and regression risks in virtualization stacks.

Technical summary

The vulnerability stems from improper initialization of memory and I/O decoding control bits in Xen's PCI device handling. When these control bits remain disabled, guest operating systems can access uninitialized host kernel memory regions, bypassing intended isolation boundaries. The incomplete nature of the CVE-2015-0777 fix suggests that the original patch addressed a symptom rather than root cause, or that additional code paths were discovered that bypassed the initial remediation. The CVSS scope change (S:C) indicates that exploitation in a guest VM can affect resources beyond the guest's security scope—specifically the host kernel.

Defensive priority

medium

Recommended defensive actions

  • Apply vendor patches from Xen Security Advisory XSA-120 to remediate incomplete fix for CVE-2015-0777
  • Review and verify memory and I/O decoding control bit configurations in Xen hypervisor deployments
  • Monitor for Debian security updates referencing DSA-4497 for additional distribution-specific guidance
  • Assess guest-to-host isolation boundaries and restrict untrusted guest workloads where patching is delayed
  • Validate that previous CVE-2015-0777 mitigations are fully superseded by CVE-2015-8553 patches

Evidence notes

CVE published 2016-04-13 per NVD record. Vendor attribution to Red Hat Enterprise Linux 5 and Xen hypervisor per CPE criteria. CVSS 3.1 vector confirms local attack vector with scope change to host. Weakness classified as CWE-200 (Information Exposure).

Official resources

2016-04-13