CVE-2015-8555

CVE-2015-8555 is a high-severity vulnerability affecting Xen versions 4.6.x, 4.5.x, 4.4.x, 4.3.x, and earlier, including Citrix XenServer. It stems from Xen's failure to properly initialize x86 FPU stack and XMM registers when XSAVE/XRSTOR are not used for guest extended register state management. This oversight allows local guest domains to potentially access sensitive information from other domains, posing a significant confidentiality risk. The vulnerability carries a CVSS v3 score of 8.6 (HIGH), indicating a critical impact on confidentiality (C:H) with network accessibility (AV:N) and low attack complexity (AC:L). While the FAUCET Risk Score is 66/100, suggesting a notable risk, the EPSS score is very low at 0.00551, implying a low probability of exploitation. Currently, there is no evidence of active exploitation, and no public exploit code exists on platforms like Metasploit or ExploitDB. Furthermore, the vulnerability has garnered minimal community discussion or media coverage, suggesting it is not a widely publicized or actively targeted threat.