SB2020070901 - Multiple vulnerabilities in Xen

Description

This security bulletin contains information about 5 secuirty vulnerabilities.

1) Race condition (CVE-ID: CVE-2020-15567)

The vulnerability allows a remote attacker to escalate privileges on the system.

The vulnerability exists due to improper management of internal resources in Xen. When mapping guest EPT (nested paging) tables, Xen would in some circumstances use a series of non-atomic bitfield writes. Depending on the compiler version and optimisation flags, Xen might expose a dangerous partially written PTE to the hardware, which an attacker might be able to race to exploit. An attacker with access to guest operating system can perform a denial of service (DoS) attack or escalate privileges on the host operating system.

Note: the vulnerability can be exploited only on systems with Intel processors.

2) Resource management error (CVE-ID: CVE-2020-15564)

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to missing alignment check in VCPUOP_register_vcpu_info hypercall in Xen. A attacker with privileged access to guest operating system can crash the hypervisor.

Note: the vulnerability affects Arm systems only.

3) Permissions, Privileges, and Access Controls (CVE-ID: CVE-2020-15565)

The vulnerability allows a remote attacker to escalate privileges on the system or perform a denial of service attack.

The vulnerability exists due to application does not properly impose security restrictions. When page tables are shared between IOMMU and CPU, changes to them require flushing of both TLBs. Furthermore, IOMMUs may be non-coherent, and hence prior to flushing IOMMU TLBs, a CPU cache also needs writing back to memory after changes were made. Such writing back of cached data was missing in particular when splitting large page mappings into smaller granularity ones. A malicious guest may be able to retain read/write DMA access to frames returned to Xen's free pool, and later reused for another purpose.

Successful exploitation of the vulnerability may allows privileges escalation on the host operating system.

Note: the vulnerability affects Intel x86 systems only.

4) Untrusted Pointer Dereference (CVE-ID: CVE-2020-15563)

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to inverted code paths in x86 dirty VRAM tracking in Xen. An attacker with access to HVM guest operating system can crash the hypervisor.

Note: the vulnerability affects x86 systems only.

5) Resource management error (CVE-ID: CVE-2020-15566)

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to improper error handling in event-channel port allocation in Xen. An attacker with access to guest operating system can consume more than 1023 event channels and crash the hypervisor.

Remediation

Install update from vendor's website.

References

• http://www.openwall.com/lists/oss-security/2020/07/07/6
• http://xenbits.xen.org/xsa/advisory-328.html
• http://www.openwall.com/lists/oss-security/2020/07/07/5
• http://xenbits.xen.org/xsa/advisory-327.html
• http://www.openwall.com/lists/oss-security/2020/07/07/4
• http://xenbits.xen.org/xsa/advisory-321.html
• http://www.openwall.com/lists/oss-security/2020/07/07/3
• http://xenbits.xen.org/xsa/advisory-319.html
• http://www.openwall.com/lists/oss-security/2020/07/07/2
• http://xenbits.xen.org/xsa/advisory-317.html