A security issue and two vulnerabilities have been reported in Xen, which can be exploited by malicious, local users in a guest virtual machine to gain knowledge of potentially sensitive information and cause a DoS (Denial of Service).
1) An error when handling XSAVE/XRSTOR instructions in the "xrstor()" function (xen/arch/x86/i387.c) when an exception is pending can be exploited to disclose certain portions of the state of floating point instructions and e.g. cryptographic keys to another domain.
Note: This security issue affects systems using AMD processors only.
Successful exploitation of this security issue requires XSAVE support to be enabled (disabled by default in versions 4.0.2 through 4.0.4 and 4.1.x).
2) An error when handling exceptions in the "xrstor()" function can be exploited to crash a host via e.g. a specially crafted data block using VCPUOP_initialise.
3) The application does not properly verify the YMM and SSE states within the "emulate_privileged_op()" function (xen/arch/x86/traps.c) before passing register values to a XSETBV instruction, which can be exploited to crash a host via invalid bit combinations.
Successful exploitation of the vulnerabilities #2 and #3 requires XSAVE support to be enabled (disabled by default in versions 4.0.2 through 4.0.4 and 4.1.x) and a PV (para-virtualised) guest.
The security issue and the vulnerabilities are reported in versions 4.0 and later.
Solution: Apply patches. Please see the vendor's advisory for details.
Provided and/or discovered by: Reported by the vendor.
Original Advisory: XEN (XSA-52, XSA-53, XSA-54):
Do you have additional information related to this advisory?
Please provide information about patches, mitigating factors, new versions, exploits, faulty patches, links, and other relevant data by posting comments to this Advisory. You can also send this
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Subject: Xen XSAVE Support Information Disclosure and Denial of Service Vulnerabilities
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