How severe is CVE-2015-8555?

CVE-2015-8555 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2015-8555 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2015-8555?

CVE-2015-8555 primarily affects Citrix Xenserver. In total, 17 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2015-8555?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2015-8555 published?

CVE-2015-8555 was published on 2016-04-13 and last updated on 2026-06-17.

CVE-2015-8555

CVE-2015-8555 is a high-severity vulnerability in Citrix Xenserver with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-200.

Key facts

Severity: High (CVSS 3.x base score 8.6)
CVSS v2: 5.0
EPSS exploit prediction: 2% (81st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-200
Affected product: Citrix Xenserver
Published: 2016-04-13
Last modified: 2026-06-17

Description

Xen 4.6.x, 4.5.x, 4.4.x, 4.3.x, and earlier do not initialize x86 FPU stack and XMM registers when XSAVE/XRSTOR are not used to manage guest extended register state, which allows local guest domains to obtain sensitive information from other domains via unspecified vectors.

Frequently asked questions

What is CVE-2015-8555?: Xen 4.6.x, 4.5.x, 4.4.x, 4.3.x, and earlier do not initialize x86 FPU stack and XMM registers when XSAVE/XRSTOR are not used to manage guest extended register state, which allows local guest domains to obtain sensitive information from other domains via unspecified vectors.
How severe is CVE-2015-8555?: CVE-2015-8555 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2015-8555 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2015-8555?: CVE-2015-8555 primarily affects Citrix Xenserver. In total, 17 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2015-8555?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2015-8555 published?: CVE-2015-8555 was published on 2016-04-13 and last updated on 2026-06-17.

References

Affected products (17)

cpe:2.3:a:citrix:xenserver:6.0:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.3.0:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.3.1:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.3.2:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.3.3:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.3.4:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.4.0:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.4.1:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.4.2:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.4.3:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.4.4:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.5.0:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.5.1:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.5.2:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.5.3:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.6.0:*:*:*:*:*:*:*
cpe:2.3:o:xen:xen:4.6.1:*:*:*:*:*:*:*

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