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VMware Tools Denial of Service

Medium

External Information

Synopsis

When utilizing shared folder functionality via vmware-tools on macOS guests, the HGFS implementation does not use adequate bounds checking when replacing illegal characters in a filename.

When sharing files with filenames containing characters that will be escaped by HGFS, it is possible to cause a stack overflow within the kernel extension installed on the guest ( com.vmware.kext.vmhgfs ), which causes the guest to crash. For example, the HGFS implementation for macOS considers colons to be an illegal character. When processing these files from shared folders (including network shares), vmware-tools escapes and replaces illegal characters, which effectively turns 1 character into 2 on the guest VM. If a filename exceeds the filesystem limitation, the guest will experience kernel panic.

As far as we are able to determine, there is no security impact beyond a Denial-of-Service condition via crashing the guest. While the end result is a stack overflow in the kernel extension, we were unable to control this in any meaningful or exploitable way.

Disclosure Timeline

April 13, 2020 - Tenable discloses issue to vendor.
April 14, 2020 - VMware acknowledges report.
April 28, 2020 - Tenable requests status update.
April 29, 2020 - VMware states that a fix is in progress.
May 29, 2020 - Tenable requests status update.
May 29, 2020 - VMware states that a fix should be ready by the end of June.
May 31, 2020 - Tenable acknowledges.
June 15, 2020 - VMware asks who to credit.
June 15, 2020 - Tenable states "Jimi Sebree of Tenable Research" and requests CVE information
June 16, 2020 - VMware provides CVE information and CVSSv3.1 numeric score
June 16, 2020 - Tenable requests clarification on CVSS score
June 19, 2020 - VMware releases advisory without notice

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

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