Xen up to 4.12.x Pagetable PV Guest input validation

Summaryinfo

A vulnerability was found in Xen up to 4.12.x and classified as problematic. Affected by this vulnerability is an unknown functionality of the component Pagetable Handler. Executing a manipulation as part of PV Guest can lead to input validation. The identification of this vulnerability is CVE-2019-19578. The attack can only be executed locally. There is no exploit available.

Detailsinfo

A vulnerability was found in Xen up to 4.12.x (Virtualization Software). It has been declared as problematic. This vulnerability affects an unknown code of the component Pagetable Handler. The manipulation as part of a PV Guest leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect availability. CVE summarizes:

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via degenerate chains of linear pagetables, because of an incorrect fix for CVE-2017-15595. "Linear pagetables" is a technique which involves either pointing a pagetable at itself, or to another pagetable of the same or higher level. Xen has limited support for linear pagetables: A page may either point to itself, or point to another pagetable of the same level (i.e., L2 to L2, L3 to L3, and so on). XSA-240 introduced an additional restriction that limited the "depth" of such chains by allowing pages to either *point to* other pages of the same level, or *be pointed to* by other pages of the same level, but not both. To implement this, we keep track of the number of outstanding times a page points to or is pointed to another page table, to prevent both from happening at the same time. Unfortunately, the original commit introducing this reset this count when resuming validation of a partially-validated pagetable, incorrectly dropping some "linear_pt_entry" counts. If an attacker could engineer such a situation to occur, they might be able to make loops or other arbitrary chains of linear pagetables, as described in XSA-240. A malicious or buggy PV guest may cause the hypervisor to crash, resulting in Denial of Service (DoS) affecting the entire host. Privilege escalation and information leaks cannot be excluded. All versions of Xen are vulnerable. Only x86 systems are affected. Arm systems are not affected. Only x86 PV guests can leverage the vulnerability. x86 HVM and PVH guests cannot leverage the vulnerability. Only systems which have enabled linear pagetables are vulnerable. Systems which have disabled linear pagetables, either by selecting CONFIG_PV_LINEAR_PT=n when building the hypervisor, or adding pv-linear-pt=false on the command-line, are not vulnerable.

The weakness was shared 12/11/2019. This vulnerability was named CVE-2019-19578 since 12/04/2019. The exploitation appears to be easy. The attack needs to be approached locally. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 03/10/2024).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The entries VDB-147008, VDB-147007, VDB-147006 and VDB-147005 are related to this item. Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Virtualization Software

Name

• Xen

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4
• 4.5
• 4.6
• 4.7
• 4.8
• 4.9
• 4.10
• 4.11
• 4.12

License

• open-source

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